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Thread: What C of C to use for IQ180 DOF calculation

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    What C of C to use for IQ180 DOF calculation

    I am looking for recommendations for the Circle of Confusion value to use for calculating the Depth of Field with an IQ180 and various lenses. I know this is somewhat subjective, but it would be useful to see what others are using to determine where to focus. My typical print size is 22x30 with lenses ranging from 40mm to 150mm for Landscape type photos. I would like to use an iPhone App to determine near and far focus limits for a given aperture and focus distance. Also, for images with distant backgrounds, does using the hyperfocal distance produce acceptable results? If not, how do you approach those situations. Thanks for your help.

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    Re: What C of C to use for IQ180 DOF calculation

    Here's a thread on this topic from last year when I was also curious:
    http://forum.getdpi.com/forum/medium...ent-mfdbs.html

    Consensus is that 2 * or sqrt(2) * pixel pitch is a good candidate for pixel peeping - best at 50%.

    Woody's feedback of 0.021/0.022 seems like a good starting point as he's shooting this combination with his IQ180 / Alpa & tech glass successfully.
    Remember: adventure before dementia!

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    Re: What C of C to use for IQ180 DOF calculation

    A fairly standard number would be 0.045 and you could think of that as the upper limit which would be good for standard viewing distance.

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    Re: What C of C to use for IQ180 DOF calculation

    In direct answer to your question the most universally accepted standard is 2 times the pixel pitch (IQ180 pixel pitch is 5.2 microns). When juggling zeros converting from microns to mm to cm (depending on what your calculator asks for) I suggest a simple google search. It's not the most powerful unit convertor out there by any means, but it's fast and easy to use.

    I find it more useful to actually start with the end product (once) and reverse engineer your own implied CoC (to use henceforth).

    Start at infinity and take several images backing away from infinity, make a composite file with a small part of each file (as it would look printed at your normal print size), make an actual print, and judge the image which is the last to still show acceptably sharp detail at infinity and then use trial and error on your app to determine the implied CoC that agrees with that result.

    The reason I suggest this is that "acceptably sharp" is the key to the CoC. This will vary based on the type of paper you use, your preference for print sharpening, viewing distance, lens sharpness, diffraction limitations, level of scrutiny, and may be influenced by more practical matters such as compromising very small amounts of infinity sharpness for a more flexible/practical foreground DOF.

    Of course this requires some careful notes (I suggest just taking an iPhone picture of the location of the focus barrel - one for each raw file you capture, it's easier and inherently more useful than trying to record a specific distance) and a solid hour or two of work, but you'd only have to do it once. The resulting implied CoC should apply to all lenses at that f-stop and print size and level of scrutiny.
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    Re: What C of C to use for IQ180 DOF calculation

    Quote Originally Posted by dougpeterson View Post
    --snip--
    Start at infinity and take several images backing away from infinity,
    --snip--
    Please don't do that as you may actually fall out of the universe.
    -bob

    Actually I find 1.4-2x pixel pitch about right for a pixel peeper such as myself.
    There are all sorts of ways to calculate it based on print size, viewing distance and the eyesight of the viewer, but if you look at stuff at 100% you will not be happy with anything other than 2 times pixel pitch.
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    Re: What C of C to use for IQ180 DOF calculation

    +1 for Bob
    I use 1.82 x pixel pitch for my DOF calculations
    For an IQ180 that is 0.0095, rounded "0.01"
    Pixel peeper value !

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    Re: What C of C to use for IQ180 DOF calculation

    Ok, I'm curious. Why 1.82x ??
    Remember: adventure before dementia!

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

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    Re: What C of C to use for IQ180 DOF calculation

    If I am using the Phase One 80mm lens, do I use the 35mm equivalent focal length of 50mm and put that into DOFMaster or do I use 80mm with the .095 CoC?

    Thanks,
    Mark

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    Re: What C of C to use for IQ180 DOF calculation

    I use 2x pixel pitch for critical work, but it's quite impractical in many situations and a compromise may be necessary. I've found it better (with an IQ160) to stop down past the diffraction limit and rescue with sharpening, rather than accept a more OOF area near or far.

    To calc in the field I have alpa's excel s/sheet opened in Numbers on an iPhone. Enough of it works that it is quite a practical solution.
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    Re: What C of C to use for IQ180 DOF calculation

    Quote Originally Posted by dougpeterson View Post

    I find it more useful to actually start with the end product (once) and reverse engineer your own implied CoC

    The reason I suggest this is that "acceptably sharp" is the key to the CoC.
    I'm with Doug on this one Steve. The issue is that it all depends on your post processing, printer output and viewing preference. The biggest being viewing preference. I have actually had customers bring a magnifying glass to inspect an 8' print that hangs in the front of my gallery. It's ludicrous but that customer purchased three 80" prints the same day so who am I to complain.

    I have a ritual with each lens and a football practice field the high school uses. After calibrating for infinity I take test shots for every aperture at 1/2 f-stop increments tethered to a laptop. I then make a chart of the DOF from infinity with two columns 100% view and 67% which matches what I usually print. Initially I did 8x10 test prints of crops at my minimum dpi to confirm what I viewed on screen was a reasonable match in print but after a few years, I know what the final print will look like.

    Depending on the subject I push down the chart to get the DOF I need. Of course the wider the DOF of the scene the farther I will stop down but I know what I will get and can balance the trade offs. Better to have an incredible scene with slight soft infinity due to refraction than not have enough DOF.

    It works for my style of shooting which almost always includes infinity. When it doesn't the focus mask and 100% preview helps fill in the gap.

    In any event, after a few outings with a new lens I have the chart (which lives on my iPhone) committed to memory and can focus in total darkness with the small light that comes with the Cambo.

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    Re: What C of C to use for IQ180 DOF calculation

    Quote Originally Posted by markymarkrb View Post
    If I am using the Phase One 80mm lens, do I use the 35mm equivalent focal length of 50mm and put that into DOFMaster or do I use 80mm with the .095 CoC?

    Thanks,
    Mark
    Focal Length as it is. This determines DoF regardless of the size of the sensor the image is falling on. The MFDB is simply capturing a larger area of the projected image than the 35mm sensor.

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    Re: What C of C to use for IQ180 DOF calculation

    Quote Originally Posted by jagsiva View Post
    This determines DoF regardless of the size of the sensor the image is falling on.
    That's odd. Sensor size is a variable in DoF calculations...



    Zeiss defines the permissible circle of confusion as 1/1500th of the sensor diagonal.

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    Re: What C of C to use for IQ180 DOF calculation

    I was referring to DoF (affected by FL, subject distance, and aperture), not CoC.

    ...two different things, as in your two statements. Zeiss is referring to sensor size as a determinant of "acceptable" CoC. Not sure how this makes your case that, "Sensor size is a variable in DoF calculations..."

    See top of page 6, no sensor size in DoF formula, just subject distance, FL and iris.
    http://www.theimagingsource.com/down...cswp.en_US.pdf

    If you reduce the subject distance in order to fill a larger format with the same FL, OR use a longer FL, to fill a larger format from the same distance, the DoF will be reduced. But this is not because of format size, but rather due to the respective change in subject distance or FL.

    BTW, I think determining the right CoC is a little more involved than 1/1500th of sensor diagonal. For example, two sensors of the same size but different resolutions will have different CoCs as pixel pitch is a factor. As several people have said above, output size is also a determinant.

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    Re: What C of C to use for IQ180 DOF calculation

    There is no Dof without a CoC. DoF is simply a way to model how we perceive an image. Until you define what permissible sharpness is, you cannot calculate DoF.

    Here is an excellent document on the subject:

    http://www.zeiss.com/c12567a8003b8b6...5_bokeh_en.pdf

    Check page page 9 for what you are talking about.

    BTW, I think determining the right CoC is a little more involved than 1/1500th of sensor diagonal.
    No, it isn't. DoF is simply calculated by a fraction of the image/sensor size--whether you find 1/1500th the diagonal matches your personal perception or not, it does not matter, you can use a different values, but it is that easy. And it does not matter if you shot fine grain film or you have tons of pixels, the DoF does not change.

    And while folks do think output size is a factor, it is not. The prime factor is viewing distance (unfortunately, folk really don't get the idea behind viewing distance and the variables in it). This is why judging DoF by 100% is not useful and become less useful as pixel resolution increases--at 100%, my 40MP 645D shows a 9mmx5mm section of the 44mmx33mm sensor. Do you think looking at a 44" x 33" print from ten inches away is a good way to judge DoF? Because that is what I am doing when I look at my 645D images at 100% on a 24" monitor.

    There is a bunch of factors in photography that are determined by the camera and how that perceives. However, there a a bunch of factors of how a person perceives an image. DoF is one of them. The model has just been developed so a photographer can understand how to influence it and to get an idea of the results. DoF is simply subjective.

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    Re: What C of C to use for IQ180 DOF calculation

    1.4x pixel pitch for extreme peepers; 2x pixel pitch for most users printing large prints, then sharpen for print output at 50%.
    Jack
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