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Thread: Diffraction vs DOF for MF wide angle lenses

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    Diffraction vs DOF for MF wide angle lenses

    I would like to hear opinions from friends at GetDPI regarding diffraction vs DOF for MF wide-angle lenses for landscape photography (without using T/S lens or focus stacking). What is the best compromise for final print?

    Thank you,
    Pramote
    Last edited by Landscapelover; 4th August 2012 at 23:46.

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    Re: Diffraction vs DOF for MF wide angle lenses

    By diffraction, I assume you are talking about sharpness of the image. DoF is another aspect of sharpness.

    First, photography as we think of it as a creative pursuit is about creating pleasing images. Pleasing is a technical term and basically states that the output is subjective--it is the observer's perception and reaction to an image. Another important point which is often lost is the photography is not comparative--the image is judged on its own merit. Comparisons are done to show changes, but images are presented individually. So when we look at an image, we want to perceive it as sharp. It does not matter if another image or set of conditions is sharper.

    Sharpness is a subjective quality as it lies in the observation of the image. It is not an absolute quality in the object. A meter is an object quality--it is either 100cm or it is not. The observation and outside conditions do not change that. Sharpness is a perceived quality based on many outside conditions like viewing conditions and the eyesight and taste of the observer. So the concept of viewing conditions arise when talking about sharpness. The standard viewing condition in the simplest form is to view an image from a distance equal to the diagonal of the area. This is a nice definition as the actual size of the image is irrelevant--the larger the image, the greater the viewing distance and so the perception of the image is always the same--a 300dpi 8x10 viewed at 12" looks the same as a 150dpi 16x20 viewed at 24" (you notice the number of pixels do not change).

    A simple definition of sharpness and DoF is to do with the smallest permissible circle of confusion that is perceived as sharp. This value is also subjective and does vary both with camera/lens manufacturers and photographers--if you don't like one set of numbers, you can make your own. Zeiss defines the permissible circle of confusion as 1/1500th of the format diagonal. DoF is related to format, not pixel pitch, as it is in relation to viewing conditions that assume a particular distance an image is viewed and in relation to the human visual system.

    Now folks will say they don't always look at an image at standard viewing distance. But here is the neat thing, the illusion of sharpness is robust and has a built-in error. The definition of a photo-quality print is 300dpi, assuming an 8x10 print viewed at about 12". To keep the math simple, than means the diagonal of the print is divided into pixels that are about 1/3000th of the image diagonal. The definition Zeiss gives for the permissible circle of confusion is 1/1500th of the diagonal. This means if you view an image at half viewing distance, the plane of focus should be acceptably sharp--a 16x20 viewed at 12" is still sharp even at 150dpi.

    MFD easily exceeds these numbers.

    So, the CoC depends on the format diagonal. Sharpness is a function of the format size and viewing condition.

    I believe you are wanting to know how far you can stop down to maximize DoF without diffraction becoming obvious. With a 6x4.5 format, f/22 or f/32 should be the diffraction limit. Your personal diffraction limit may be different. I routinely stop my 645D and P25+ down to f/16. I sometimes use f/22, but that is getting o my threshold. But it is not a simple thing, high-contrast scenes work better and unsharp masking makes a huge difference. When I got my camera I did some tests. I shot some usual condition all the way down to f/22 and made 36" prints form them. The benefit of the added DoF certainly outweighed the impact of diffraction--sharpness is not what you see at 100% when comparing it to other conditions. I would urge you to test yourself to see the results, and by results, I mean going to a print.

    Now, as much as I respect my fellow photographers, we all suffer from too much experience. We can see the defects in an Ansel Adams print from 200m. We have come to learn to recognize very small changes in the image. We obsess over individual pixels. But the audience does not see nor care about the minutia. What they see is a great, sharp image. I have never had someone walk up to me and ask about the diffraction in my print.

    I hope that answers your question.
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    Re: Diffraction vs DOF for MF wide angle lenses

    Much appreciate my friend!
    It is a very thoughtful comment from someone who really knows about photography/publishing.
    Again, my question is about the "print", not the "pixel peep".

    Thanks
    Last edited by Landscapelover; 5th August 2012 at 09:58.

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    Re: Diffraction vs DOF for MF wide angle lenses

    Quote Originally Posted by Shashin View Post
    The definition Zeiss gives for the permissible circle of confusion is 1/1500th of the diagonal. This means if you view an image at half viewing distance, the plane of focus should be acceptably sharp--a 16x20 viewed at 12" is still sharp even at 150dpi.

    MFD easily exceeds these numbers.

    So, the CoC depends on the format diagonal. Sharpness is a function of the format size and viewing condition.
    I see that several people agree with you... but some of us buy MFD to produce pictures bigger than 10 * 8 " inches, and which can be observed from distances closer than the diagonal... if not then why not use an iPhone?

    Were big pictures, like 40 foot frescos, made to be observed from the diagonal?

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    Re: Diffraction vs DOF for MF wide angle lenses

    Quote Originally Posted by dick View Post
    I see that several people agree with you... but some of us buy MFD to produce pictures bigger than 10 * 8 " inches, and which can be observed from distances closer than the diagonal... if not then why not use an iPhone?

    Were big pictures, like 40 foot frescos, made to be observed from the diagonal?
    I never said anything about limiting print size to 8x10. Basically, print size is not a factor and viewing distance closer than standard will work very well.

    Comparing a fresco to a photograph is not very meaningful and really has nothing to do with the topic.

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    Re: Diffraction vs DOF for MF wide angle lenses

    Quote Originally Posted by Shashin View Post
    I never said anything about limiting print size to 8x10. Basically, print size is not a factor and viewing distance closer than standard will work very well.

    Comparing a fresco to a photograph is not very meaningful and really has nothing to do with the topic.
    You said:
    So, the CoC depends on the format diagonal.
    ...and who could try to make us believe that... ¿except for a pro who is still trying to do professional photography with a 6Mpx camera?

    (If you use a low res camera and look at the picture from far enough away, it looks not too bad,)

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    Re: Diffraction vs DOF for MF wide angle lenses

    Dick, you must be right! What an articulate argument--how did you know I was a Pro using a 6MP camera?

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    Re: Diffraction vs DOF for MF wide angle lenses

    Quote Originally Posted by Landscapelover View Post
    I would like to hear opinions from friends at GetDPI regarding diffraction vs DOF for MF wide-angle lenses for landscape photography (without using T/S lens or focus stacking). What is the best compromise for final print?

    Thank you,
    Pramote
    I think the specificity of "landscape photography" and wide angle lenses lends itself to Shashin's opinion to some degree ... where it is more about pictorial qualities of a viewed print ... the boundries of which may be somewhat subjective from photographer-to-photographer.

    However, Dick has a point in general. In my experience, f/11 for MFD becomes the point of more careful scrutiny because of final usage. I strive for an optimal f/5.6 or f/8 and revert to T/S when I routinely push past it too frequently to get visual acuity front to back ... but I do not shoot landscapes.

    I have done images that were enlarged 6 to 10 feet wide and used in trade-show booths where the images will be viewed closer than normal, even inspected for product detail. Or images that are massively cropped to show a detail.

    Also have had images made into photo murals for corporate lobbies, although those aren't viewed at nose-close distances usually.

    The other application of W/A optics is industrial inspection where details are important.

    -Marc

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    Re: Diffraction vs DOF for MF wide angle lenses

    Quote Originally Posted by fotografz View Post
    However, Dick has a point in general.
    Really? Apart from his charm, he has not actually said anything. LOL

    In my experience, f/11 for MFD becomes the point of more careful scrutiny because of final usage. I strive for an optimal f/5.6 or f/8 and revert to T/S when I routinely push past it too frequently to get visual acuity front to back ... but I do not shoot landscapes.
    So, my point is it is subjective--determined by a viewer. You seem to be saying exactly the same thing.

    And yes, I print big. I just did a 7x10 foot image for a museum.

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    Re: Diffraction vs DOF for MF wide angle lenses

    Quote Originally Posted by Shashin View Post
    Really? Apart from his charm, he has not actually said anything. LOL



    So, my point is it is subjective--determined by a viewer. You seem to be saying exactly the same thing.

    And yes, I print big. I just did a 7x10 foot image for a museum.
    Yes, I was agreeing with you, especially given the specificity of the OP's question ... but not dismissing Dick's opinion (blunt or not) because the applications he referenced are ones I have faced many times.

    It is one thing to have a person gazing at a landscape at some normal distance where it can all be taken in, and a mechanical engineer inspecting a part on a 10' machine photo at a trade show, or a museum curator or art lecturer inspecting the brush strokes of a painting, or an art director cropping a 1" section of fabric from a 15" piece to show detail in a catalog, or some product shot with slightly fuzzy DOF when the retoucher goes to knock out the background, etc. etc. etc.

    I also think it differs a bit lens to lens, but that is just an impression not a tested fact.

    -Marc

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    Re: Diffraction vs DOF for MF wide angle lenses

    I really don't think people are reading what I wrote. First, I defined the area I am discussing--that is the creation of a pleasing image and in reference to maximizing DoF. I also do scientific and reproduction imaging and the underlying assumptions still hold true--you can print large for a trade show and if you know that you are photographing for 1/4 viewing distance condition, you can plan your shoot accordingly, nothing I wrote really changes except the emphasis on DoF.

    Also, I am not simply saying this for standard viewing distance, but also for shorter than standard. The illusion of sharpness under standard models is robust, as I explain. You can walk up to a print and it holds together. If you are printing large, you certainly cannot maintain a 300dpi "native" resolution, if you follow some arguments about what CoC is required. Nor do you need to.

    And more pixels do not make an image softer--the underlying assumption for setting the CoC to 100%. Take a sharp image and print it large. Resample the image to give it more pixels and print it the same size. The difference? Nothing. Putting more pixels on a sensor likewise does not make the resulting images softer.

    Another thing that is being missed is the CoC defines an upper limit. An image will have CoCs smaller than that limit.

    I don't think we are really disagreeing.

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    Re: Diffraction vs DOF for MF wide angle lenses

    There's an App. It accounts for both DOF and defraction. No kidding. Here's a link:

    OptimumCS-Pro. It's not totally intuitive but it seems to work.
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    Re: Diffraction vs DOF for MF wide angle lenses

    DoF is directly related to focal length -- the shorter the focal length, the deeper the DoF. Diffraction is directly related to aperture and nominal CoC, or in the case of digital imaging, the pixel pitch. Thus, like every other decision surrounding gear choices, there is a tradeoff of benefits and no free lunches... That said, generally speaking you will have greater apparent DoF with shorter lenses and smaller physical sensors, but other aspects of image quality will change/suffer in proportion. It's why MF looks different than FF DSLR, and FF DSLR looks different than M4/3rds when all are enlarged to the same size prints. Which looks best is largely subject and personal-preference dependent, though I have found most people's personal preferences seem to lean toward the "MF look" being "superior" -- even if they cannot clearly express the specifics of why they feel that way...

    However, I don't think any of the above has anything to do with creating "the best" possible art. To my thinking, that is achieved whenever the artist clearly conveys their message with whichever gear they've chosen to use, period. In that, I have seen spectacular works produced with M4/3rds and equally crappy work produced with MF; I've also seen spectacular work produced with MF and crappy work produced with M4/3rds. It aint the arrow being used, it's the indian behind them putting them to use.

    But that's me and I respect others opinions will vary.
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    Re: Diffraction vs DOF for MF wide angle lenses

    Thanks everyone for your thoughtful comments. I really appreciate them.
    Jack..What f-stop you will use for IQ 180 with SK 55mm to get the best DOF from few feet to infinity (No focus stacking or T/S)?
    Thanks.
    Pramote

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    Re: Diffraction vs DOF for MF wide angle lenses

    We love to debate about DoF definitions, which ends up on CoC size.

    Originally DoF was defined something like this: "just sharp enough for a relaxed viewing condition for people with average vision". This is what Ansel Adams used and all other great photographers in the film era.

    Then came digital. Tastes have changed.

    We now like even sharper images, and the gear can do it and the prints are possible. I prefer, and I see many others do the same a new DoF definition along the line "the edge of the DoF is so sharp it is virtually indistinguishable from the plane of focus even at close inspection, after post-processing sharpening has been applied". That is if you focus at the hyperfocal distance the infinity should not look blurry even at 100% pixel peep.

    According to my own experiments I find a CoC set to the larger of 2x pixel pitch and airy disk diameter is a good choice to match this definition, and since we use small apertures in landscape airy disk diameter is always the larger one.

    So how small apertures can we use? Smaller than we did with large format film (relative to the film size)! The thing is that deconvolution sharpening is rather effective, a tool we did not have back in the film days, so we can blur down the image with quite some diffraction and sharpen it back up again to fine results. So how small can we go? It is hard to say something absolute since it is a matter of taste. With my medium format system I shoot f/11 when I can but go all the way to f/32 if I have to. If I used 8x10" film instead the equivalent apertures would be about f/64 for f/11 and f/165 or so for f/32, and as we know many of large format lenses are actually limited to f/64... so DoF has become easier with digital (smaller apertures, better sharpening), so I think it is perfectly ok to adapt the newer more stringent definition of DoF with the smaller CoC.

    How you relate to DoF is also very much a personal style and also scene dependent, some like to let things go slightly blurry to give the image more depth. Concerning DoF tables and hyperfocal distances etc which I use when out shooting I prefer the new tighter definition of DoF though, I think it is a better more well-defined reference to relate to. When it comes to the technical aspect of landscape photography most of us are interested in making the image "as sharp as the gear and scene allows" rather than "no sharper than required for a relaxed viewing condition".
    Last edited by torger; 9th August 2012 at 07:02.

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    Re: Diffraction vs DOF for MF wide angle lenses

    Quote Originally Posted by Shashin View Post
    If you are printing large, you certainly cannot maintain a 300dpi "native" resolution, .
    I am not an advocate of Pan-and-stitch, but it can give you 300 original camera pixels per print inch on 10 foot pictures... and move-and-stitch (photographing in sections) could do for a 40 foot fresco!
    Take a sharp image and print it large. Resample the image to give it more pixels and print it the same size. The difference? Nothing.
    This is correct if the raster image processor makes the most of the file. With high quality Multi-Shot files up-sampling might help, but, again it depends how well the printer software would do the same job.
    Quote Originally Posted by Jack View Post
    DoF is directly related to focal length -- the shorter the focal length, the deeper the DoF. , generally speaking you will have greater apparent DoF with shorter lenses and smaller physical sensors,
    Yes, Jack, but I think, technically, DoF is dependent on magnification ¿Which is, I think, what you are saying? and if we use a lens of double the focal length from double the distance, we get the same magnification and very similar DoF.

    You get better apparent DoF with low-res cameras and cheap lenses, because the CoC is relatively larger, and if nothing is very sharp then slightly out of focus looks relatively sharp.

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    Re: Diffraction vs DOF for MF wide angle lenses

    Quote Originally Posted by Landscapelover View Post
    Thanks everyone for your thoughtful comments. I really appreciate them.
    Jack..What f-stop you will use for IQ 180 with SK 55mm to get the best DOF from few feet to infinity (No focus stacking or T/S)?
    Thanks.
    Pramote
    If one would use my model it works like this - the more you stop down the more diffraction you get, and then you should increase the CoC to mirror that it can be larger without noticing a difference from the plane of focus. CoC = Airy disk diameter I think is an excellent choice. Then you just feed this into your hyperfocal formula and get the focus distance and near limit. The larger f-number the nearer limit but more diffraction to deal with in sharpening.

    Example using CoC=Airy disk diameter for 55mm

    f/11: 17.8 meters hyperfocal distance, near limit half of that 8.9 meters
    f/16: 8.9, 4.5
    f/22: 4.5, 2.3
    f/32: 2.3, 1.2

    unfortunately I did not have a table in feet, but multiply with 3 you get an approximate. As you can see for each stop you increase the hyperfocal distance is halved.

    This will give you so sharp images that if you nose your print you cannot see any difference between the plane of focus and the DoF edge, which is usually want one will want if you have something important at infinity.

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    Re: Diffraction vs DOF for MF wide angle lenses

    Quote Originally Posted by dick View Post
    You get better apparent DoF with low-res cameras and cheap lenses, because the CoC is relatively larger, and if nothing is very sharp then slightly out of focus looks relatively sharp.
    Exactly. If the small camera would have equal number of megapixels and be able to fully resolve them there would be no difference. Larger sensor + longer focal length can in full be compensated with smaller aperture (unless we hit an upper limit of the lens which can be the case for large format film) at the cost of longer shutter speed. Yes we get more diffraction, but it is a zero-sum game, 20 megapixels on a large sensor can accept more diffraction than 20 megapixels on a small one.

    Appearent DoF concerning viewing condition is dependent on sooo many factors. A worst case: detailed landscape scene printed big hanged in a gallery at comfortable viewing height, people will in addition to see the whole picture walk close to look at the details. A best case: a portrait hanged above a fireplace - you can't come close and you would not want to either, portraits are preferably viewed so you can see all at once.

    Due to this I have dropped the traditional large CoC definition and instead use tables with small CoC (=Airy disk diameter), then I know where it is "critically sharp", and when the scene is such that I can or should relax it I do, but I think it is much easier to have the "critically sharp at close inspection"-DoF as reference. The basis for this to work though is a camera where you can stop down much and sharpen well, which applies to all digital cameras but not to large format film.

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    Re: Diffraction vs DOF for MF wide angle lenses

    Thanks very much Torger. It is very useful information.

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    Re: Diffraction vs DOF for MF wide angle lenses

    Quote Originally Posted by torger View Post
    ...if you focus at the hyperfocal distance the infinity should not look blurry even at 100% pixel peep.

    According to my own experiments I find a CoC set to the larger of 2x pixel pitch and airy disk diameter is a good choice to match this definition, and since we use small apertures in landscape airy disk diameter is always the larger one.
    This is the definition of Hyperfocal distance, and is, technically, not disputable... But Merklinger's book "The ins and outs of Focus" suggest that we should focus nearer to infinity.

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    Re: Diffraction vs DOF for MF wide angle lenses

    Quote Originally Posted by dick View Post
    This is the definition of Hyperfocal distance, and is, technically, not disputable... But Merklinger's book "The ins and outs of Focus" suggest that we should focus nearer to infinity.
    I do that myself too, since even if I overshoot hyperfocal distance by 50% or something the exponential behavior of DoF leads to that I still gain quite much in near limit than compared to focusing at infinity.

    Example: 50mm f/11 hyperfocal distance is 14.8 meters, if focused exactly there we get DoF from 7.4 to infinity. If we overshoot by as much as 50% to 22 meters we still get sharp result from 8.8m (we lost 1.4 meters in near limit), while if focusing at infinity we get from 14.8m (lost 7.4 meters).

    Overshooting a bit also guarantees a really sharp infinity, and the typical scene where hyperfocal applies we have fine structures at infinity (a forest-covered hill, a mountain etc) while up close the structures are generally larger and it hurts less if those are a bit soft.

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    Re: Diffraction vs DOF for MF wide angle lenses

    So, lets walk the walk. This is a test I actually did to find out how far I can push the system. I took an image under very bad light as the systemic resolving power is related to target contrast--so the image is not going to be as sharp as under direct light. Not only is this an overcast day, it is in a rather dark forest. This is also ISO400--I do a lot of handheld work and push my ISO as well. although this image was taken on a tripod. (Note: curves were applied because the original is flat and unsharp masking as well--no noise reduction.)



    On the left is the entire image. It was shot at the diffraction limit of the system or close to it--f/22. The image on the right is a 100% crop and most likely not at the focal plane. This represents a 4.9mm x 4.6mm section of the 44x33mm sensor. If I made this into a 4x3 ft. print (and I printed this personally to 3 ft.), you are viewing a 5"x5" section of that print.

    Digital photography has not rewritten imaging science. CoC is still a factor of format and not pixel pitch--you can check Zeiss's wonderful online pdf on DoF and Bokeh and you can visit the Cambridge Color web site. I also have a shelf full of books saying the same thing. While pixel peeping is a really neat thing to do and provides useful information, it is not a great way to definitively judge sharpness nor DoF. And the more pixels a sensor has, the less relevant the 100% view gets.

    BTW, like I stated in my original post in this thread, I personally avoid the diffraction limit as I personally do not like it. But I have done great work at f/16 and do not hesitate to use it. I do on occasion shoot at f/22 when I need to.

    My best suggestion is try and test (and in the field it is easy to take DoF field brackets--you don't need to stick to one). There are a lot of factors that influence sharpness--there are conditions, like the one above, where I would be hesitant to use small apertures--the test was just confirming for me where my limits were. I do not recommend playing by numbers which seems to be the fashion--"f/8 is the optimal aperture so stick to only that" kind of thing. There are really good reasons to give up a little at the plane of focus to gain something because of DoF--and this goes both with opening up or stopping down.
    Last edited by Shashin; 9th August 2012 at 09:34.
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    Re: Diffraction vs DOF for MF wide angle lenses

    Quote Originally Posted by Shashin View Post
    CoC is still a factor of format
    Saying this again will not make it true...

    You say:
    you can print large for a trade show and if you know that you are photographing for 1/4 viewing distance condition, you can plan your shoot accordingly,
    ¿So CoC is a factor of the cropped format that corresponds to the smallest section of the image that a viewer will look at?

    ...and I am aware that people (and organisations, and books) have, for decades, assumed that the observer of the picture will always want to see the whole picture, and not move in closer to see more detail... Would it be nice if we could move on?

    ¿When people use a Canon lens on MFD, do they re-calculate their CoC so that they get no more res on MFD than they would have had using the same lens on 35mm?

    ¿If I want a high res image, and shift-and stitch with a 120mm lens instead of using a 60mm lens, do I re-calculate the CoC for the larger effective format, so that I get no more res? ...or do I do it so that I can print big at 360 original camera pixels per print inch, so that viewers can get close to the image to appreciate (the fine detail in) small sections of the image?

    Perhaps you could try to see my logic instead of believing what you have read in books?

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    Re: Diffraction vs DOF for MF wide angle lenses

    Again it is about what the purpose of DoF calculations are. Traditional CoC and DoF theory is all about "acceptable sharpness" for relaxed viewing conditions. That thinking also leads up to that more than a 4 megapixel camera is a waste, because if you stand a bit away from the print, have average vision and don't care that much it will be acceptably sharp. We've all seen tests where prints from compact cameras are indistinguishable from ones made with medium format, and sure this happens when viewing conditions are relaxed. That "image science" has indeed not changed.

    But when it comes to shooting technique, would you strive for making the sharpest possible image for the given situation, or just "sharp enough" for a relaxed viewing condition? The recommendations for tripods etc would look quite different if we were into "sharp enough" -- of course we want "as sharp as possible"!

    In that case DoF tables and hyperfocal distances based on traditional CoC are not helping us making the proper decisions. Traditional tables will indicate that we can shoot at large apertures and will lead to an unnecessarily sharp plane of focus and blurry DoF edge. It is a waste! The logical error with this is that when we choose CoC as the smallest spot we can see it is meaningless to have anything sharper than that, so why don't we just stop down until the plane of focus is as blurry as the DoF edge?

    This is what CoC = Airy disk is all about. These tables will show DoF where the plane of focus in no sharper than the DoF edge even when nosing the print, and it takes diffraction into account. This will cause us to stop down more not less than if using tables with a large CoC.

    With film there were reasons to not stop down much, 1) you could not do it at all (large format cameras rather limited in minimal aperture), 2) overly long shutter speeds (large film formats require very small apertures and thus long shutter speeds) 3) the small aperture effects contrast loss and diffraction could not be compensated for in post-processing as effectively as we can digitally. So in that case it made sense to have a relaxed DoF since we needed a tradeoff with less diffraction and larger apertures.

    With digital we are not limited in the same way so we can find a much better balance between diffraction blur (and shutter speed) and CoC blur to give a more detailed overall image. As a comparison, for many 8x10" lenses the smallest aperture is f/64, the equivalent aperture for my 48x36mm sensor is f/11 (64/5.5 crop factor) which actually is the largest aperture I shoot landscapes at!

    I may buy into that shooting at a larger aperture and have blurry DoF edges can give the image a more layered 3D look, a subtle depth, but I think that only makes sense when you actually have a main subject to focus at, so the plane of focus it at some logical position for the composition (i e not hyperfocal and generally not when tilted). In those cases I often let some stuff be outside the stringent DoF and blur slightly.
    Last edited by torger; 9th August 2012 at 11:08.

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    Re: Diffraction vs DOF for MF wide angle lenses

    Quote Originally Posted by dick View Post
    Saying this again will not make it true...

    You say:
    ¿So CoC is a factor of the cropped format that corresponds to the smallest section of the image that a viewer will look at?

    ...and I am aware that people (and organisations, and books) have, for decades, assumed that the observer of the picture will always want to see the whole picture, and not move in closer to see more detail... Would it be nice if we could move on?

    ¿When people use a Canon lens on MFD, do they re-calculate their CoC so that they get no more res on MFD than they would have had using the same lens on 35mm?

    ¿If I want a high res image, and shift-and stitch with a 120mm lens instead of using a 60mm lens, do I re-calculate the CoC for the larger effective format, so that I get no more res? ...or do I do it so that I can print big at 360 original camera pixels per print inch, so that viewers can get close to the image to appreciate (the fine detail in) small sections of the image?

    Perhaps you could try to see my logic instead of believing what you have read in books?
    The format is the image area--cropping and stitch impact that. The trouble with amateurs is you get little pieces of information and really don't understand how they go together. Perhaps you can make a little effort to study this and come back when you understand the fundamentals.

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    Re: Diffraction vs DOF for MF wide angle lenses

    Quote Originally Posted by torger View Post
    Again it is about what the purpose of DoF calculations are. Traditional CoC and DoF theory is all about "acceptable sharpness" for relaxed viewing conditions. That thinking also leads up to that more than a 4 megapixel camera is a waste, because if you stand a bit away from the print, have average vision and don't care that much it will be acceptably sharp. We've all seen tests where prints from compact cameras are indistinguishable from ones made with medium format, and sure this happens when viewing conditions are relaxed. That "image science" has indeed not changed.
    You are misrepresenting what the science does. To say there is no point on having a high-resolution system mean you have missed the point and also don't understand the image is a collection of resolutions and details over the area. The science is a model to predict the perception of certain qualities in an image. Nor is it a fixed model. Your visual system can actually perceive details smaller than what it can resolve--this is called detection. So a system exceeding the basic limit of the defined CoC is still impacting the image and in ways that can be perceived. But sharpness is not a definition of detail.

    But when it comes to shooting technique, would you strive for making the sharpest possible image for the given situation, or just "sharp enough" for a relaxed viewing condition? The recommendations for tripods etc would look quite different if we were into "sharp enough" -- of course we want "as sharp as possible"!
    But "sharp as possible" is a subjective call and there are two sides to that. If you don't have enough DoF, then the image is not as sharp as possible and you will have to pay for getting that with the effect of diffraction.

    In that case DoF tables and hyperfocal distances based on traditional CoC are not helping us making the proper decisions. Traditional tables will indicate that we can shoot at large apertures and will lead to an unnecessarily sharp plane of focus and blurry DoF edge. It is a waste! The logical error with this is that when we choose CoC as the smallest spot we can see it is meaningless to have anything sharper than that, so why don't we just stop down until the plane of focus is as blurry as the DoF edge?
    That is a personal evaluation. DoF is simply a model. CoC values can be chosen to help you visualize what your condition produce. But these CoC values are not absolute. If a set of values does not seem good to you, you can change them, this is why difference lens manufacturers have used different values.

    You yourself have redefined the values based on your personal work. The trouble is you are taking your subjective choice and saying this is now true for everyone. The normal DoF model assumes an average human response and so is the best starting point. Just because you have refined the number for your self does not undermine the theory. And certainly folks still zone focus with lenses and so the theory works regardless of your personal frame.

    This is what CoC = Airy disk is all about. These tables will show DoF where the plane of focus in no sharper than the DoF edge even when nosing the print, and it takes diffraction into account. This will cause us to stop down more not less than if using tables with a large CoC.
    If that work for you, fine. But I am not talking about personal preferences or advice. To say the size of the Airy disk, and really it is not the Airy disk unless you image point sources, is the defining attribute make no sense in relation to format. The spot size in reference to the entire image area defines the point--it does make a difference if it is 1/1500th, 1/3000th, 1/7000th of the image size. Absolute frames are not helpful. And this is why simply adding pixels to an image does not softer nor does it change the DoF.

    With film there were reasons to not stop down much, 1) you could not do it at all (large format cameras rather limited in minimal aperture), 2) overly long shutter speeds (large film formats require very small apertures and thus long shutter speeds) 3) the small aperture effects contrast loss and diffraction could not be compensated for in post-processing as effectively as we can digitally. So in that case it made sense to have a relaxed DoF since we needed a tradeoff with less diffraction and larger apertures.

    With digital we are not limited in the same way so we can find a much better balance between diffraction blur (and shutter speed) and CoC blur to give a more detailed overall image.
    There are reasons not to stop down much with digital. Will will also notice that the minimum aperture for film camera lenses were different based on format.

    Exposure time is irrelevant here. BTW, unsharp masking is originally a film technique.

    I think you have completely missed my the point of my posts. I am not say you stop to any particular aperture. I am simply showing how the attributes of DoF and diffraction work together and their limits. I am not doing this from a personal opinion based on my working method. But I am working from the definitions of DoF and my experience in seeing it in real terms. It works.

    I have also stated if you want to redine it for your personal work, as you have, you can.

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    Re: Diffraction vs DOF for MF wide angle lenses

    Quote Originally Posted by Shashin View Post
    The format is the image area--cropping and stitch impact that. The trouble with amateurs is you get little pieces of information and really don't understand how they go together. Perhaps you can make a little effort to study this and come back when you understand the fundamentals.
    ...and I thought that it is you who is quoting clichés out-of-context without understanding what you are talking about?

    I have the advantage of being an engineer, and understanding technology... and there are many amateurs here who know more than most pros - but that is not saying much.

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    Re: Diffraction vs DOF for MF wide angle lenses

    Shashin, we probably agree more than we think. I think we both end up in using about the same apertures :-). I'm not sure I'm arguing against you in some way even, I just try to explain my view on DoF in a little bit more detail. I surely agree that we can define CoC to whatever we like depending on what our purpose with it is.

    What I try to say is that the traditional DoF with fixed large CoC (0.2mm for 8x10, 0.1 for 4x5, 0.03 for 35mm etc) which often end up in tables here and there and for hyperfocal advice etc do not give the results most digital users expect.

    Digital users don't expect when they pixel peep their image that the infinity is blurry when they have used hyperfocal technique. A digital user would then have preferred to stop down more and focus farther ahead, which happens to provide a sharper image (or equally sharp) for all viewing conditions than the original one.

    The traditional DoF tables are more about describing what is seen in a typical relaxed viewing condition after the print is made, rather than helping the digital user to achieve optimal result in the field which provides best possible input to make prints for various viewing conditions.

    Nearly always someone asks about how to achieve the sharpest image. Then I think talking about the fuzzy subjective viewing condition-based DoF, "it depends on what you want etc" does not really help much.

    I say there is another way :-), a way to look at DoF that helps anyone optimize their shooting technique out in the field so that regardless of viewing condition of the final print there's the best input for it.

    I actually use DoF/hyperfocal/tilt tables out in the field to make actual decisions about aperture, if it is better to tilt than to use hyperfocal, etc. CoC = Airy disk works. The resulting DoF is easy to understand what it means, a good reference point for deep DoF photography that helps you optimize your technique. It is also well-balanced, it does not lead to insanely small apertures, at the "emergency apertures" you really have lots of DoF.

    Why Airy disk? Because landscape apertures are always diffraction-impacted in modern cameras so one does not need to care about pixel pitch, and it makes no sense to have a smaller CoC that the Airy disk since it defines the resolution limit (sort of, CoC = 0.8xAiry disk is probably more exact but at this level, the pixel level, it is not important). Why not larger than the Airy disk? Because if our goal is to get deep DoF and we have important stuff within it it makes no sense to give more sharpness in the plane of focus than at the DoF edges, then it is better to stop down more increase diffraction and get more DoF.

    There are some subtle things around this of course but this DoF definition is very understandable and good to use as reference to make modifications from. But of course, if someone finds using a fixed size 0.04mm CoC more useful that's ok.

    I don't want to claim that "my method" (I was certainly not first to use it) is some sort of ultimate truth, I just try to explain why it is really useful to base DoF calculations on that if you intend to use it out in the field when you do landscape photography, and why focusing based on traditional DoF tables do not give as good results.

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    Re: Diffraction vs DOF for MF wide angle lenses

    torger, I agree, we may be just running up against syntax.

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    Re: Diffraction vs DOF for MF wide angle lenses

    Quote Originally Posted by dick View Post
    ...and I thought that it is you who is quoting clichés out-of-context without understanding what you are talking about?

    I have the advantage of being an engineer, and understanding technology... and there are many amateurs here who know more than most pros - but that is not saying much.
    Sorry Dick, but bullying has never really worked on me. You can shoot off as many personal attacks as you like. I really don't care if you are an engineer--one field does not translate into another.

    I really feel sorry for you.

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    Re: Diffraction vs DOF for MF wide angle lenses

    Quote Originally Posted by Landscapelover View Post
    Thanks everyone for your thoughtful comments. I really appreciate them.
    Jack..What f-stop you will use for IQ 180 with SK 55mm to get the best DOF from few feet to infinity (No focus stacking or T/S)?
    Thanks.
    Pramote
    You can't do 2 feet to infinity with a 55 over the IQ180 without tilts. You can barely get 10 feet to infinity without tilts at f16, and f16 is sub-optimal due to excessive (at least for my tastes) diffraction.
    Jack
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    Re: Diffraction vs DOF for MF wide angle lenses

    Quote Originally Posted by Landscapelover View Post
    I would like to hear opinions from friends at GetDPI regarding diffraction vs DOF for MF wide-angle lenses for landscape photography (without using T/S lens or focus stacking). What is the best compromise for final print?

    Thank you,
    Pramote
    back to the original question.
    "Best" compromise on DOF vs diffraction.
    I doubt that there is one "Best".
    DOF in a print viewed at a distance of its diagonal measure depends on the diagonal measure of the sensor as cropped, the focal length of the lens, and the aperture used.
    Diffraction has only to do with the numerical aperture. When diffraction is extreme, it will soften the whole image, so that the sharpest areas will begin to visibly blur, but those areas that already are OOF may blur, but I doubt one would notice a difference. As a general practice I try to shoot at f/8 or f/11 maybe 16 at the small end just so I do not limit my cropping options. At "normal" viewing distances for a full frame image you can probably lose a bit of sharpness because folk's eyes are not that good.
    If on the other hand, your customers are photographers primarily, then all prints are viewed at nose-length distance and through a hand glass. In that case your COC=about 1.414 times your pixel pitch and you need to shoot at f/8.
    In reality, there is a lot more flexibility for the usual crowd.
    A case in point, I sold a 17 by 24 image of a 6 Mpix file awhile ago. It was not even particularly sharp or that well focused.
    It is hanging in an office lobby over a sofa.
    I almost refused to print it, but the client is thrilled and as far as she is concerned it is "perfect" and even better, she paid.
    So the answer to your question is a big "depends"
    -bob
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    Re: Diffraction vs DOF for MF wide angle lenses

    What Bob said ... It depends. For mortal viewers I think Shashin and the vast majority of material on the CoC/DoF seem correct. For pixel peepers it's different rules applying.

    What I do know is that I've yet to read one of these threads without someone getting their whiteys in a twist at some point. Not one - yet.
    Remember: adventure before dementia!

    As Oscar Wilde said, "my tastes are simple, I only like the best"
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    Re: Diffraction vs DOF for MF wide angle lenses

    Quote Originally Posted by GrahamWelland View Post
    getting their whiteys in a twist
    Huh? Can you help us non-native speakers? Even the urban dictionary failed to help me :-)

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    Re: Diffraction vs DOF for MF wide angle lenses

    Quote Originally Posted by torger View Post
    Huh? Can you help us non-native speakers? Even the urban dictionary failed to help me :-)
    Ok, how about panties in a bunch?
    Remember: adventure before dementia!

    As Oscar Wilde said, "my tastes are simple, I only like the best"

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    Re: Diffraction vs DOF for MF wide angle lenses

    Quote Originally Posted by Bob View Post
    A case in point, I sold a 17 by 24 image of a 6 Mpix file awhile ago. It was not even particularly sharp or that well focused.
    It is hanging in an office lobby over a sofa.
    I almost refused to print it, but the client is thrilled and as far as she is concerned it is "perfect" and even better, she paid.
    So the answer to your question is a big "depends"
    Great story . I've sometimes hopelessly tried to point out quality differences between print A and print B which to me are obvious and significant, but the non-photographer (and even photographers too) do not see it or do not care.

    One must face it that there is really a small amount of people that can even see a difference if a print was shot with a medium format system with excellent technique rather than a hand-held compact camera, or care about it if they happen to see a difference.

    Fine print quality is a connaisseur thing. Usually the most picky connaisseur is the photographer that shot the image and made the print, certainly not the customers, but sometimes the customer might be a picky photographer...

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    Re: Diffraction vs DOF for MF wide angle lenses

    Quote Originally Posted by torger View Post
    Huh? Can you help us non-native speakers? Even the urban dictionary failed to help me :-)
    "Tightie-Whities" are slang for men's white underwear briefs ... "in a bunch" or "twisted" refers to uncomfortable and irritating ...making the wearer "cranky" ... which in turn means ill-tempered.

    Somehow when you have to explain it, it loses a lot

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    Re: Diffraction vs DOF for MF wide angle lenses

    Quote Originally Posted by Bob View Post
    back to the original question.
    "Best" compromise on DOF vs diffraction.
    I doubt that there is one "Best".
    DOF in a print viewed at a distance of its diagonal measure depends on the diagonal measure of the sensor as cropped, the focal length of the lens, and the aperture used.
    Diffraction has only to do with the numerical aperture. When diffraction is extreme, it will soften the whole image, so that the sharpest areas will begin to visibly blur, but those areas that already are OOF may blur, but I doubt one would notice a difference. As a general practice I try to shoot at f/8 or f/11 maybe 16 at the small end just so I do not limit my cropping options. At "normal" viewing distances for a full frame image you can probably lose a bit of sharpness because folk's eyes are not that good.
    If on the other hand, your customers are photographers primarily, then all prints are viewed at nose-length distance and through a hand glass. In that case your COC=about 1.414 times your pixel pitch and you need to shoot at f/8.
    In reality, there is a lot more flexibility for the usual crowd.
    A case in point, I sold a 17 by 24 image of a 6 Mpix file awhile ago. It was not even particularly sharp or that well focused.
    It is hanging in an office lobby over a sofa.
    I almost refused to print it, but the client is thrilled and as far as she is concerned it is "perfect" and even better, she paid.
    So the answer to your question is a big "depends"
    -bob
    Quote Originally Posted by Jack View Post
    You can't do 2 feet to infinity with a 55 over the IQ180 without tilts. You can barely get 10 feet to infinity without tilts at f16, and f16 is sub-optimal due to excessive (at least for my tastes) diffraction.
    Jack & Bob..Thanks very much.
    Does it mean that the only ways I can achieve DOF from few feet to infinity for the IQ 180 with insignificant diffraction are T/S (probably from a Tech Camera) and focus stacking?

    Tim Fitzharris, an award winning nature & landscape photographer, published a lovely book "National Audubon Society Guide to Landscape Photography" in 2007. He used Mamiya with non-digital (even manual ones) Mamiya lenses and Phase One P25 throughout his book with f/16 and f/22. His pictures looked fantastic. He also claimed they looked great on his big prints.
    His approach was quite different from more recent comments concerning diffraction. Does a smaller MP DB (P25) make difference?

    Pramote

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    Re: Diffraction vs DOF for MF wide angle lenses

    Quote Originally Posted by Landscapelover View Post
    His approach was quite different from more recent comments concerning diffraction. Does a smaller MP DB (P25) make difference?

    Pramote
    yes - the 9u sensor works better with stopped down lenses in my experience. I also have a P25+ and it gives you a lot more leeway with f-stop usage for pixel peeping images. As Bob alluded, 1.414 x sensor pitch (9u) gets you to pixel peeping CoC twice as large as you'll get with the IQ180 (5.5u).

    Btw, I also have that book and remember that the high gloss print sharpened images look super sharp at the small size. I'm sure his larger prints look fine too but (ducks for cover) it depends on how big they are and how close you are when viewing them.
    Remember: adventure before dementia!

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    Re: Diffraction vs DOF for MF wide angle lenses

    Quote Originally Posted by Landscapelover View Post
    ...Phase One P25 throughout his book with f/16 and f/22. His pictures looked fantastic. He also claimed they looked great on his big prints.
    His approach was quite different from more recent comments concerning diffraction. Does a smaller MP DB (P25) make difference?

    Pramote
    Quote Originally Posted by GrahamWelland View Post
    yes - the 9u sensor works better with stopped down lenses in my experience. I also have a P25+ and it gives you a lot more leeway with f-stop usage for pixel peeping images. As Bob alluded, 1.414 x sensor pitch (9u) gets you to pixel peeping CoC twice as large as you'll get with the IQ180 (5.5u).
    Yes... but the physical (format) size is the problem, as DoF depends on magnification, which depends on format size... so, if anybody made a quality, high-res 35mm or micro-4/3 camera ¿and made the sensor available in a digiback? it would be great for landscapes and macro... my GH2 is a good camera for the money, but the files fall apart when you try to do any adjustments in Photoshop, especially if you use high ISO.

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    Re: Diffraction vs DOF for MF wide angle lenses

    Well, neither the P25+ nor IQ files fall apart in photoshop at either 22mp or 80mp. If anything it's the colour that is a concern in PS as you pull the files apart. 14bit colour trounces 12bit or less. Resolution, even in big prints, tends to be less of a "real" issue by the time the printer and printer driver have had their way.

    I know that you chose to skip my second paragraph but I did relate to the output size which has a direct correlation to perceived DoF & ultimately sharpness perception (influenced also by how close you are too).
    Remember: adventure before dementia!

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    Re: Diffraction vs DOF for MF wide angle lenses

    Quote Originally Posted by Landscapelover View Post
    Jack & Bob..Thanks very much.
    Does it mean that the only ways I can achieve DOF from few feet to infinity for the IQ 180 with insignificant diffraction are T/S (probably from a Tech Camera) and focus stacking?

    Tim Fitzharris, an award winning nature & landscape photographer, published a lovely book "National Audubon Society Guide to Landscape Photography" in 2007. He used Mamiya with non-digital (even manual ones) Mamiya lenses and Phase One P25 throughout his book with f/16 and f/22. His pictures looked fantastic. He also claimed they looked great on his big prints.
    His approach was quite different from more recent comments concerning diffraction. Does a smaller MP DB (P25) make difference?
    I got myself a tech camera and use tilt in I would guess 50% of my images. Tilt often provides you with better options, but it depends a lot on your style. If you have high stuff close (tight forest scenes etc) tilt don't help much, but if you often do open scenery tilt helps a lot. Personally I think focus stacking is a mess, there's always some artifact in there, and I prefer to make one shot images. I go f/32 + some pieces out of focus before I consider focus stacking, but that's my personal decision.

    But as discussed above having the sharpest possible picture is not that important for smaller sizes and relaxed viewing conditions, and even if viewing conditions are such that one can see that the image is not tack sharp few cares. Image content is all that matters.

    Still as a photographer one may like to make sharp pictures and because one appreciates it oneself. If it weren't for that (and other subtle quality aspects) I think digital medium format would be dead by now.

    Concerning tilt vs not having tilt some have a shooting style where you focus at a main subject and you consider that other parts in the picture is a bit less sharp is an advantage, give it a subtle depth. Therefore some landscape shooters can have an IQ180 and never use tilt. Using tilt and shift is for me an integrated part of my photographic process, I simply enjoy using it and it do give me subtle image quality properties I like, but the main reason I use them is simply because I enjoy making pictures "view camera style", it's fun.

    There's an interesting aspect about diffraction, which is that it is not a hard limit. This means that if you shoot f/22 with a 80 megapixel back you get slightly more total resolution than f/22 with a 20 megapixel back, but the more diffraction there is diminishing returns. I recently saw an interesting print comparison test, and then a 36 megapixel D800 f/22 carefully deconvolution sharpened and contrast corrected produced as good print result as a 20 megapixel camera at f/8 (also sharpened)! Extremely low noise levels (as the D800 has) improves the possibility to deconvolve as that type of sharpening increases noise.

    P25 is only 22 megapixels, the pixels are huge, 9 um. This means that on a pixelpeep level you get less affected of small apertures, so f/16 and even f/22 does look quite sharp at 100% on screen. But as stated above, f/22 on an 80 megapixel IQ180 + sharpening would still make an even sharper print, although it would look fuzzier at the pixelpeep level.

    People were happy with 22 megapixels back then, and from an artistic standpoint it is of course enough. But if we have paid tens of thousands of dollars to get an IQ180 rather than a second hand P25 for a couple of grands we surely want to make as sharp images as that IQ180 can do, even if most of our audience would not notice or care.
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    Re: Diffraction vs DOF for MF wide angle lenses

    Quote Originally Posted by fotografz View Post
    "Tightie-Whities" are slang for men's white underwear briefs ... "in a bunch" or "twisted" refers to uncomfortable and irritating ...making the wearer "cranky" ... which in turn means ill-tempered.

    Somehow when you have to explain it, it loses a lot

    -Marc
    Thanks for saving me times to look in online dictionary
    I really appreciate the comments (not only the "Tightie-Whities"). It's hard to get this information anywhere except GetDPI and LUL.

  44. #44
    Administrator Bob's Avatar
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    Re: Diffraction vs DOF for MF wide angle lenses

    Quote Originally Posted by Landscapelover View Post
    Jack & Bob..Thanks very much.
    Does it mean that the only ways I can achieve DOF from few feet to infinity for the IQ 180 with insignificant diffraction are T/S (probably from a Tech Camera) and focus stacking?

    Tim Fitzharris, an award winning nature & landscape photographer, published a lovely book "National Audubon Society Guide to Landscape Photography" in 2007. He used Mamiya with non-digital (even manual ones) Mamiya lenses and Phase One P25 throughout his book with f/16 and f/22. His pictures looked fantastic. He also claimed they looked great on his big prints.
    His approach was quite different from more recent comments concerning diffraction. Does a smaller MP DB (P25) make difference?

    Pramote
    Yes it does, it is all about how much the imager needs to be magnified.

    If you print a full 6x4.5 film frame and focus your 55 at 20 feet and f/11 it may appear to have a dof from 10 feet to infinity for an average viewer looking at the print from a distance equal to the diagonal, but it will not look that way if you zoom way in. If you were to be shooting film this is what the calculations would say. Frankly digital is no different, except that we love to pixel peep. Only a few of us nuts would judge film sharpness by looking at it through a microscope and then you would be hard pressed to find any
    If you were to print that same file in a book for example, it would look fine assuming sharpening usual for the printing process.
    That is pretty much reality, but for me, as a microscope user, I would use tilts
    Likes 3 Member(s) liked this post

  45. #45
    Senior Member dchew's Avatar
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    Re: Diffraction vs DOF for MF wide angle lenses

    Quote Originally Posted by Landscapelover View Post
    Does a smaller MP DB (P25) make difference?

    Pramote
    My opinion is different on this question. I know there is a CoC vs. pixel size calculation, but that is relevant to 100% screen pixel peeping, not printing. In my head the lower magnification of prints created with larger sensors and higher MP neutralizes all this.

    It's like the common question about diffraction limitations when comparing lenses. A sharper f/4 lens will say the best aperture is f/8, compared to a less-sharp f/5.6 lens that says the best aperture is f/11. So does that mean if I want to shoot at f/11 I would be better off with the f/5.6 lens? Of course not! At f/11 the f/4 lens will still be equal or better than the other lens. It just won't be as sharp as itself at f/8.

    There is more depth of field in smaller formats at a given f-stop on screen. But once I print a Micro 4/3 image at the same print size as an IQ180 printed image, the DoF becomes exactly the same (assuming equal subject distance and aperture). Even if it is just an 8x10 inch print. I always thought the core reason MF is still acceptable at higher apertures like f/11 - f/22 vs. the 35mm format is simply because the image magnification is lower.

    In other words, at higher aperture you may not gain anything by having a larger format or more MP, but you would be hard pressed to find a situation where you would lose something in a print.

    Dave

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