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Thread: Do the math - focal length and Format demystified

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    Senior Member pegelli's Avatar
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    Re: Do the math - focal length and Format demystified

    Quote Originally Posted by Annna T View Post
    Personnally I find it way too exaggerated to say that mirrorless manufacturers are lying to their clients and cheating them.
    In my mind it's further that that, it's plain wrong. All phenomena discussed are governed by the laws of physics and optics. How can it be cheating if that's what's happening. Yes there are key differences between formats, well documented in good scientific and photographic literature but they are very far away from cheating. In the end it will influence IQ (as fotografz pointed out) but it also reminds me of AA's stern advice: "there is nothing worse than a sharp picture of a fuzzy concept".

    I think the only cheats are the people who are blowing this "problem" out of proportion with half truth and omitting key information because it suits their story (or sales) better.
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    Re: Do the math - focal length and Format demystified

    I just spoke about this with Dietmar Wüller of Image Engineering (probably one of the few experts worldwide besides People like Dr. Nasse from Zeiss maybe - which I will also try to ask about it....as I can ) for maybe 15minutes now
    .
    The problem is:
    1) it is additionally scale dependent, macro will differ from infinity
    2) there are some other formulas involved to make it scientifically stringent
    and thus there is no SINGLE Formula where you can calculate this.

    Fact is though: if you look at the Image appearance, this is definitely right as the video describes it. Or as Lloyd descibes it.
    The part with the photons (differing exposure), amount of exposure is completely left out to trial and error, as there are no correllating data for any sensors available (at least not in easy Public access) that could be used to define this.

    He gave me a link for the formulas he once descibed for depth of field on differing formats, which is kind of a mathematical proof for the part of the differing depth of field (in german only-sorry), but as there are so many superior math geniuses around here, they may easily understand the formulas without an english explanation....

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    Re: Do the math - focal length and Format demystified

    MFDB will slowly become obsolete, just like 4x5 and 8x11 view cameras. Offering a small portable view camera able to mount an A7r in the rear standard could be a hit

    The question isn't whether the manufacturers of smaller sensors are cheating them, the question is whether the price/size advantages are big enough to compensate for the IQ differences, an IQ difference which is getting smaller and smaller.
    Anna T

    Fotodiox has adapters to mount FF to 4x5. Pair this with an Ebony or Chamonix, and you have a very portable 4x5 dslr.

    http://www.bhphotovideo.com/bnh/cont...=REG&A=details

    This discussion is likely too esoteric for the photographer/artist who find these drawn out threads to be less controversial. I often find the most technical photographers tend to have the most boring portfolios anyway. I think Stefan was just trying to share something he thought interesting. Go film...
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    Re: Do the math - focal length and Format demystified

    Ok, so now I watched the video. Best entertainment I've seen since reviewing the footage with my dentist at my last root canal.

    By this guy's calculations my 8x10 Sinar P2 was the only honest camera I ever owned. But only when I had that huge Nikkor T 800mm f/12 ED mounted up in that Copal 3 shutter.

    All the rest of my cameras have been lying to me! I always knew there was something sneaky that lived inside those old 'Blads, but I never suspected gremlins living in my new Sony A7R!

    This stuff just makes my brain hurt. I don't see the art in any of it.

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    Re: Do the math - focal length and Format demystified

    Boy, this thread continues to amaze me.

    When I shoot with film, I shoot with everything from 8x11mm Minox format to 6x9cm medium format cameras. Who's lying to me then about focal length and aperture?

    Same thing with digital capture. There are a bunch of interchangeable lens camera formats ... from 1" like the Nikon 1 to FT to APS-C to FF to MFDB and LF scanning backs.

    The only people who can be interpreted as lying about anything are people who believe in this idiotic "35mm FF über alles" supremacy and insist that anything that looks vaguely like a 35mm film camera MUST BE a 35mm format or it isn't what its manufacturer says it is.

    Different formats have different sizes, which influences lens physical size, field of view of the same focal length lenses across formats, Depth of Field, imaging characteristics, etc etc. It is no different from how it always was in the film world except this "35mm FF über alles" nonsense wants to make it different for some unknown (and likely marketing-money driven) reason.

    Same for this insane OCD discussion of "Image Quality". As someone else said along the way, I don't nave to reduce every photograph to some arcane set of specifications of contrast, resolution, MTF curves, mid-tone micro contrast, dynamic range deliberation, et cetera ad nauseam to say "Hey, that's a good photograph! I like it!" I can recognize with my eyes a good lens from a bad one, a good rendering from a bad one, well enough.

    I know enough about sensors, optics, formats, FoV, DoF, etc that I don't need some engineer to tell me how basic photographic principles work. Never mind some video blogger rambling on nonsensically about how one camera company is lying compared to another.

    Enough of this nonsense for me. I'm quite happy with how my cameras perform, with how the pictures I make appear, from whatever format I choose to work with. And I don't need to debate whether one is lying to me or not in the perception of people whom I wouldn't listen to anyway if they sat in the pulpit at the local evangelical tent.

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    Re: Do the math - focal length and Format demystified

    Chuck -

    well it probably depends on what you are demanding for your money ?

    Lets say you go to your Photodealer of your choice and want to buy a brand new LEICA DG NOCTICRON 1,2/42,5mm H-NS043 for whopping 1500 € (around 2000 $ US).
    At home you shoot this lens and (it may or may not equal absolute exposure depending on the technology of your used MFT sensor, most likely it will NOT be the same as most new FF 24x36 sensors) but even worse - the image does not look like a f1,2/85mm (which is the actual used terminology in ads) but exactly like a 2.0/85mm on 35mm FF - both on open aperture (added to clarify even more !!!) ?

    Wouldn´t you feel cheated ? Especially as a good 2,0/85mm from Nikon, Canon or SonyFF costs only about 1-/4th to 1/5th of this ?

    Of course this lens may be the best of the best and you say you don´t care if it is so superior, but additionally you are limited to 16 Mpix resolution whereas the 24x36 FF rise to 36mpix ?

    Totally out of relevance ?

    Really ?
    Last edited by Stefan Steib; 20th May 2014 at 07:38.
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    Re: Do the math - focal length and Format demystified

    Quote Originally Posted by Stefan Steib View Post
    At home you shoot this lens and (it may or may not equal absolute exposure depending on the technology of your used MFT sensor, most likely it will NOT be the same as most new FF 24x36 sensors) but even worse - the image does not look like a f1,2/85mm (which is the actual used terminology in ads) but exactly like a 2.0/85mm on 35mm FF ?
    Have you entered an "equivocation of the week" contest?

    ... may or may not ...
    ... most likely ...

    And, from an earlier post (at 15:17):
    "Guy - this will be my last post in this thread."

    Seems we can't believe anything you post.

    -----

    It seems Godfrey and I agree for once.
    I shoot Ilford FP4+ in all formats from 35mm through 8x10, and get exactly the same results using many different lenses.

    I also shoot digital in formats from toys through medium (Hasselblad).
    Exposures (based on nominal ISO speed) are consistent throughout that range.

    Stefan, I fail to understand what point you may be trying to make.

    - Leigh

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    Re: Do the math - focal length and Format demystified

    Quote Originally Posted by Leigh View Post

    Stefan, I fail to understand what point you may be trying to make.

    - Leigh
    Yes - I see that you don´t understand.

    Greetings from Germany
    Stefan
    because photography is more than technology - and " as we have done this all the time "
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    Re: Do the math - focal length and Format demystified

    Quote Originally Posted by Stefan Steib View Post
    Chuck -

    well it probably depends on what you are demanding for your money ?

    Lets say you go to your Photodealer of your choice and want to buy a brand new LEICA DG NOCTICRON 1,2/42,5mm H-NS043 for whopping 1500 € (around 2000 $ US).
    At home you shoot this lens and (it may or may not equal absolute exposure depending on the technology of your used MFT sensor, most likely it will NOT be the same as most new FF 24x36 sensors) but even worse - the image does not look like a f1,2/85mm (which is the actual used terminology in ads) but exactly like a 2.0/85mm on 35mm FF ?

    Wouldn´t you feel cheated ? Especially as a good 2,0/85mm from Nikon, Canon or SonyFF costs only about 1-/4th to 1/5th of this ?

    Of course this lens may be the best of the best and you say you don´t care if it is so superior, but additionally you are limited to 16 Mpix resolution whereas the 24x36 FF rise to 36mpix ?

    Totally out of relevance ?

    Really ?
    Yes. Really.

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    Re: Do the math - focal length and Format demystified

    Quote Originally Posted by Stefan Steib View Post
    Chuck -

    well it probably depends on what you are demanding for your money ?

    Lets say you go to your Photodealer of your choice and want to buy a brand new LEICA DG NOCTICRON 1,2/42,5mm H-NS043 for whopping 1500 € (around 2000 $ US).
    At home you shoot this lens and (it may or may not equal absolute exposure depending on the technology of your used MFT sensor, most likely it will NOT be the same as most new FF 24x36 sensors) but even worse - the image does not look like a f1,2/85mm (which is the actual used terminology in ads) but exactly like a 2.0/85mm on 35mm FF ?

    Wouldn´t you feel cheated ? Especially as a good 2,0/85mm from Nikon, Canon or SonyFF costs only about 1-/4th to 1/5th of this ?

    Of course this lens may be the best of the best and you say you don´t care if it is so superior, but additionally you are limited to 16 Mpix resolution whereas the 24x36 FF rise to 36mpix ?

    Totally out of relevance ?

    Really ?
    Hi Stefan,
    First off, let's dial back the rhetoric a notch or two, and make sure we are all talking about the same thing, because from the vitriol in this thread we clearly are not.

    You and your friend that made the video are looking at the glass half full. I'm not even looking at a glass, I am looking at a set of tools, if you get my drift. I hear your objections, and understand your possibly valid concerns about how the industry chose to express its arcane wisdom over time. Remember though before tossing the whole baby out with the bathwater, there is a lot of history behind those choices. History for creating beautiful, well crafted images, not animated pixel comparison graphs or charts.

    You ask do I have concern about a LEICA DG NOCTICRON 1,2/42,5mm on my GH3 not looking like an f1,2/85mm on my Canon 5D Mark III? No, actually I am not. If it did, it wouldn't be any dang good to me either, because Canon already has that covered with the excellent Canon 85mm f/1.2. You've got it backwards.

    I would buy the LEICA DG NOCTICRON 1,2/42,5mm for my GH3 to go the OTHER way. In other words, @f8 using the Nocticron, I get total depth of field EXTENDED by two stops, closeup to infinity. Don't forget, in a filmmakers bag of tricks, different sensor sizes are great creative tools as well. You may not like the laws of physics, but we all have to live by them, and to be better photographers, learn to use them to our creative advantage.

    If I wanted an 85mm f/1.2 look, I would pull out a 5D Mark III with a Canon 85mm f/1.2. I don't horse around with all those "math computations" your talking about when I am out shooting, nor do I carry my Captain America secret decoder ring. I carry a good light meter, a complete set of primes, a vision of what I want, and the experience collected over the years to help guide me in choosing the right camera sensor size, correct angle, and correct lenses to capture it - at the correct exposure.

    I don't have the luxury of the time to run an Excel spreadsheet to compute anything. My clients rightly expect I get familiar with my gear, learn how to use it and what it can do in my own time, and then show up ready to complete the work I contracted with them to produce.

    As a DP, I am responsible for deciding I need a GH3 & 12mm @f/2.8 for the look I am after. Or alternatively, maybe it is an 85mm f/1.2 Canon 5D Mark III look that is called for. Both are equally valid options, and both equally exclusive each to the other. I can't get the GH3 to look like the 5D anymore than I can get the 5D to look like the GH3. Or the Fuji X-E1 or the Sony A7R or the tiny Zoom Q4. They all look different, even with the same lens and the best grading suite in the business. MF & LF, same thing. Formats are options too.

    What you seem to be saying is a conspiracy by camera manufacturers to somehow cheat the population, I as an artist see as viable creative options I wouldn't want to loose. Hope that helps to understand where some of us are coming from, and what we consider is relevant.
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    Re: Do the math - focal length and Format demystified

    Quote Originally Posted by Chuck Jones View Post
    Hi Stefan,
    First off, let's dial back the rhetoric a notch or two, and make sure we are all talking about the same thing, because from the vitriol in this thread we clearly are not.

    You and your friend that made the video are looking at the glass half full. I'm not even looking at a glass, I am looking at a set of tools, if you get my drift. I hear your objections, and understand your possibly valid concerns about how the industry chose to express its arcane wisdom over time. Remember though before tossing the whole baby out with the bathwater, there is a lot of history behind those choices. History for creating beautiful, well crafted images, not animated pixel comparison graphs or charts.

    You ask do I have concern about a LEICA DG NOCTICRON 1,2/42,5mm on my GH3 not looking like an f1,2/85mm on my Canon 5D Mark III? No, actually I am not. If it did, it wouldn't be any dang good to me either, because Canon already has that covered with the excellent Canon 85mm f/1.2. You've got it backwards.

    I would buy the LEICA DG NOCTICRON 1,2/42,5mm for my GH3 to go the OTHER way. In other words, @f8 using the Nocticron, I get total depth of field EXTENDED by two stops, closeup to infinity. Don't forget, in a filmmakers bag of tricks, different sensor sizes are great creative tools as well. You may not like the laws of physics, but we all have to live by them, and to be better photographers, learn to use them to our creative advantage.

    If I wanted an 85mm f/1.2 look, I would pull out a 5D Mark III with a Canon 85mm f/1.2. I don't horse around with all those "math computations" your talking about when I am out shooting, nor do I carry my Captain America secret decoder ring. I carry a good light meter, a complete set of primes, a vision of what I want, and the experience collected over the years to help guide me in choosing the right camera sensor size, correct angle, and correct lenses to capture it - at the correct exposure.

    I don't have the luxury of the time to run an Excel spreadsheet to compute anything. My clients rightly expect I get familiar with my gear, learn how to use it and what it can do in my own time, and then show up ready to complete the work I contracted with them to produce.

    As a DP, I am responsible for deciding I need a GH3 & 12mm @f/2.8 for the look I am after. Or alternatively, maybe it is an 85mm f/1.2 Canon 5D Mark III look that is called for. Both are equally valid options, and both equally exclusive each to the other. I can't get the GH3 to look like the 5D anymore than I can get the 5D to look like the GH3. Or the Fuji X-E1 or the Sony A7R or the tiny Zoom Q4. They all look different, even with the same lens and the best grading suite in the business. MF & LF, same thing. Formats are options too.

    What you seem to be saying is a conspiracy by camera manufacturers to somehow cheat the population, I as an artist see as viable creative options I wouldn't want to loose. Hope that helps to understand where some of us are coming from, and what we consider is relevant.

    Chuck, well said. Thank you.

    I consider it absolutely wonderful to have all these choices and the competition between equipment makers to keep costs down. Besides the creative choices/reasons you list there are also other ones that make me prefer one tool or format over another one for a given situation. For example bulk or weight considerations. I use everything from my iPhone to iPad, E-M5, E-M1, NEX-5N, NEX-7, D40, D200, D300, D3, M9, A7R, and D800E. I even used a G3 and S95. What's not to like?

    I find the technical progress that has been made in the last few years quite amazing. With an A7R as a back MF isn't out of reach for me anymore. Even light field cameras might get advanced enough to become interesting tools, not just novelties.

    I suspect some who inject cheating into this discussion are driven by ulterior motives. Enough said!
    Last edited by k-hawinkler; 20th May 2014 at 08:45.
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    Re: Do the math - focal length and Format demystified

    Quote Originally Posted by Stefan Steib View Post
    I just spoke about this with Dietmar Wüller of Image Engineering (probably one of the few experts worldwide besides People like Dr. Nasse from Zeiss maybe - which I will also try to ask about it....as I can ) for maybe 15minutes now
    .
    The problem is:
    1) it is additionally scale dependent, macro will differ from infinity
    2) there are some other formulas involved to make it scientifically stringent
    and thus there is no SINGLE Formula where you can calculate this.

    Fact is though: if you look at the Image appearance, this is definitely right as the video describes it. Or as Lloyd descibes it.
    The part with the photons (differing exposure), amount of exposure is completely left out to trial and error, as there are no correllating data for any sensors available (at least not in easy Public access) that could be used to define this.

    He gave me a link for the formulas he once descibed for depth of field on differing formats, which is kind of a mathematical proof for the part of the differing depth of field (in german only-sorry), but as there are so many superior math geniuses around here, they may easily understand the formulas without an english explanation....

    » Blog Archiv » Schärfentiefe

    Greetings from Germany
    Stefan
    Here is an English paper on DoF:

    http://www.smt.zeiss.com/C12567A8003...5_Bokeh_en.pdf

    Yes, you can make similar, but not identical, images from difference systems. That is not new. But the video is saying so much more.

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    Re: Do the math - focal length and Format demystified

    Quote Originally Posted by Stefan Steib View Post
    Chuck -

    well it probably depends on what you are demanding for your money ?

    Lets say you go to your Photodealer of your choice and want to buy a brand new LEICA DG NOCTICRON 1,2/42,5mm H-NS043 for whopping 1500 € (around 2000 $ US).
    At home you shoot this lens and (it may or may not equal absolute exposure depending on the technology of your used MFT sensor, most likely it will NOT be the same as most new FF 24x36 sensors) but even worse - the image does not look like a f1,2/85mm (which is the actual used terminology in ads) but exactly like a 2.0/85mm on 35mm FF - both on open aperture (added to clarify even more !!!) ?

    Wouldn´t you feel cheated ? Especially as a good 2,0/85mm from Nikon, Canon or SonyFF costs only about 1-/4th to 1/5th of this ?

    Of course this lens may be the best of the best and you say you don´t care if it is so superior, but additionally you are limited to 16 Mpix resolution whereas the 24x36 FF rise to 36mpix ?

    Totally out of relevance ?

    Really ?
    Actually, if that is what you think, then the problem is not with the lens nor the camera. We cannot fix the ignorance of the buyer. The best way is to educate yourself on optics and photography. Unfortunately, with the video you posted, you will not find help there.

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    Re: Do the math - focal length and Format demystified

    Quote Originally Posted by Stefan Steib View Post
    Smaller stops (larger f numbers) produce a longer depth of field,
    Only when ALL OTHER FACTORS REMAIN EQUAL. And that's not the case in the video description. As stated earlier, f-number is simply the ratio of focal length to aperture diameter as a determination of luminance. It is but one factor in determining DoF, and image magnification size as well as CoC are critical.
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    Re: Do the math - focal length and Format demystified

    Shashin

    Thanks for posting the link to Dr. Nasses´s article, that would have been the next one I would have linked too. See the table on page 10. There - I forgot - is even a larger format reference to 4,5/6 6/9 and 4/5". QED.

    There are therefore equivalent f-numbers
    for all formats, corresponding to the linear format
    size.


    Next: even if some people dislike it, but it is pretty safe to say that smaller sensors collect less light. Exception: when their pixels are the same size as of a bigger one and thus have a smaller resolution. - which is why we don´t see actual MFT´s go beyond 18 Mpix - which is around 36Mpix on the Sony A7R.

    Next: on this level of equal pixel size and probably CMOS architecture, the photon count wil probably be similar. but then next:

    By the lack of higher resolution the additional depth of field may not be of relevance at all because it may not even be recorded (depends on the subject and focusing distance - hence "may").

    Next: it is pretty safe to say that a 21,7 Mpix FF24x36 like a Canon 5DIII will have a significant higher photon collection ability than a much smaller sensor with the same resolution on half of the chip-area.

    I still wonder why this is disputable.

    And lastly: if the industry decides to advertise their lenses for formats with other sizes with equivalents to 35mm, they probably also should change the given image result description by valueing the real comparable aperture equivalent and write f2,0 when this lens is an f.stop of 1,2. The other - probably a better - solution would be to introduce a clear description of a factor number to describe the actual depth of field value comparable to the absolute first opening.

    Pretty easy, but why isn´t that done nor mentioned ?

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    Re: Do the math - focal length and Format demystified

    Chuck - You are kidding right ? You must be kidding.

    Ok- you tell me (transferred to 35mm)instead of using an FA Zeiss 1,8/55mm and stop it down to f 16 when needed you would do the same preferrably with an Otus 1,4/55mm for 2500 € more, even if this technically doesn´t make any sense at all ?

    or staying at the original example using a Nocticron 1,2/42,5mm for 1500€ even if e.g. the M.Zuiko Digital 1,8/45mm costs 329 € and there is (very likely - especially on Video!) not any visible difference at f8 ?


    Congrats. You must have won in the lottery. All others should maybe calculate their spendings instead of paying for a myth.

    Regards
    Stefan

    Quote Originally Posted by Chuck Jones View Post

    I would buy the LEICA DG NOCTICRON 1,2/42,5mm for my GH3 to go the OTHER way. In other words, @f8 using the Nocticron, I get total depth of field EXTENDED by two stops, closeup to infinity. Don't forget, in a filmmakers bag of tricks, different sensor sizes are great creative tools as well. You may not like the laws of physics, but we all have to live by them, and to be better photographers, learn to use them to our creative advantage.

    If I wanted an 85mm f/1.2 look, I would pull out a 5D Mark III with a Canon 85mm f/1.2. I don't horse around with all those "math computations" your talking about when I am out shooting, nor do I carry my Captain America secret decoder ring. I carry a good light meter, a complete set of primes, a vision of what I want, and the experience collected over the years to help guide me in choosing the right camera sensor size, correct angle, and correct lenses to capture it - at the correct exposure.

    .
    because photography is more than technology - and " as we have done this all the time "
    facebook:hcam.de - www.hcam.de - www.hartblei.de

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    Re: Do the math - focal length and Format demystified

    Is this pissing match still going on?
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    Re: Do the math - focal length and Format demystified

    I've given up cause maths are really not my thing but can I say that I like the guys goatee and wish mine looked as good?
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    Re: Do the math - focal length and Format demystified

    Quote Originally Posted by Ben Rubinstein View Post
    but can I say that I like the guys goatee and wish mine looked as good?
    I thought he kinda looked like this guy...

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    Re: Do the math - focal length and Format demystified

    Quote Originally Posted by Stefan Steib View Post
    Shashin

    Thanks for posting the link to Dr. Nasses´s article, that would have been the next one I would have linked too. See the table on page 10. There - I forgot - is even a larger format reference to 4,5/6 6/9 and 4/5". QED.

    There are therefore equivalent f-numbers
    for all formats, corresponding to the linear format
    size.
    No one said you cannot correlate DoF among formats, but to get there, it requires additional variables beyond f-number. The video claims that f-number is a measure of DoF. That is not true. Also, this is a very limited statement--true at infinity, not so at short object distances.

    This simple statement, and it is incomplete, is simply an easy way to make comparisons between formats. It is much harder to take this and make universal statements about photography. And it is pretty useless beyond buy a new system. When you take a photograph, do you think in terms of a format you are not using or do you think in terms of the camera you have in your hand?

    Next: even if some people dislike it, but it is pretty safe to say that smaller sensors collect less light. Exception: when their pixels are the same size as of a bigger one and thus have a smaller resolution. - which is why we don´t see actual MFT´s go beyond 18 Mpix - which is around 36Mpix on the Sony A7R.
    So, by this statement, you are saying that smaller sensors may or may not collect less light. Not a useful statement.

    Next: on this level of equal pixel size and probably CMOS architecture, the photon count wil probably be similar. but then next:

    By the lack of higher resolution the additional depth of field may not be of relevance at all because it may not even be recorded (depends on the subject and focusing distance - hence "may").
    DoF is not dependent on pixel resolution.

    Next: it is pretty safe to say that a 21,7 Mpix FF24x36 like a Canon 5DIII will have a significant higher photon collection ability than a much smaller sensor with the same resolution on half of the chip-area.

    I still wonder why this is disputable.
    First, pixel area is important in relation to exposure and S/N, not sensor area. Or are you saying you are losing light if you crop you image later? Pixels are the smallest indivisible element of a picture. How many photons one pixel gathers is independent of all the other pixels around it. The fact that a larger sensor has more photon strikes is irrelevant to the image in regards to S/N or the image in itself. It is the photon strikes per pixel.

    And lastly: if the industry decides to advertise their lenses for formats with other sizes with equivalents to 35mm, they probably also should change the given image result description by valueing the real comparable aperture equivalent and write f2,0 when this lens is an f.stop of 1,2. The other - probably a better - solution would be to introduce a clear description of a factor number to describe the actual depth of field value comparable to the absolute first opening.

    Pretty easy, but why isn´t that done nor mentioned ?

    Regards
    Stefan
    First, the industry understands the people don't get how format size changes field of view. They use the fudge of crop factor and equivalent focal length to communicate to consumers. So, when you understand that this is a method to counter people's ignorance, then you would want to question the consumer knowledge, not photo science.

    Focal length is focal length. Sensor size does not change that. That is why the lens description is given in the actual focal length. For some consumer cameras, manufacturer have used equivalent focal lengths (Dimage 7, for example), but there again, it is for consumer ignorance (and you cannot remove the lens). And if you use any equations in photography, plugging in equivalent focal lengths is going to give wrong answers. Focal length is a real optic property independent of field of view.

    And the same with f-number. The f-number given with the lenses is absolutely correct. f-number simply defines the illumination at the image plane. That is it. It is used for exposure.

    What you are proposing is the f-number is a measurement of DoF. That is absolutely false. Folks have a hard enough time with crop factors now, but equivalent DoF given if f-number are really going to confuse these poor saps. How the hell are they going to figure out exposure? Is it the first f-number or the second? Then when you realize that your f-number/DoF scheme is only going to work at infinity and to calculate an effective f-number at some other distance, the whole problem becomes a mess. And you cannot plug in equivalent f-numbers into equations either and get the right result.

    This is what I propose. Why not just use focal length and f-numbers to mean what they actually do mean and let photographers educate themselves instead of inventing crazy schemes?
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    Re: Do the math - focal length and Format demystified

    @ Will:

    Or as I said before:

    " The other - probably a better - solution would be to introduce a clear description of a factor number to describe the actual depth of field value comparable to the absolute first opening."

    Otherwise we mostly agree. What is creating additional confusion is the terminology. By demanding a terminology to be correct and allowed to criticise, but on the other hand tolerate that the focal lenght and the valid behaviour of the lens are spelled different you introduce Orwellian Zwiedenk here. I get your point about not unneccessary confusing people.

    But then you see how confused many people are now, even if they call themselves Pros !

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    Re: Do the math - focal length and Format demystified

    One of the biggest problems that was created years ago was using the term focal length and putting a number on it like 24mm lens or 50mm. Back than everything was full frame in photography given the format. Today with APS , m3/4 and so on we are stuck with these multiplication factors to deal with to find the equivalent to FF. What they should have done back in yesteryear was called lenses by there angle of view. Than any lens made in any format change the consumer would go by angle of view. Than all this conversion stuff would have been eliminated. Okay that ship passed a long time ago
    Photography is all about experimentation and without it you will never learn art.

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    Re: Do the math - focal length and Format demystified

    Guy

    EXACTLY !!! I was just thinking to type that when you did !

    A hint for people who are somewhat lost with all this:

    There is a very nice app (well there are more but this is the best I know) called "Angle of View" which can be used on iOS.

    https://itunes.apple.com/us/app/angl...ew/id452946973

    if you want to spend a bit more and you are into cinema/Video too get PCam

    https://itunes.apple.com/us/app/pcam...295456485?mt=8

    This is maybe the best tool to easily understand the differing formats and that is very helpful. Makes it much less abstract.

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    Re: Do the math - focal length and Format demystified

    Now if they did this if you wanted a 74 degree angle of view in any format than you buy that lens that is in that format system. Easy Peasy.

    I think this is actually a 24mm in FF. But if they created that system a lot of confusion would have been eliminated. Not all but some

    Im still having a issue with loss of light on format change, not sure I am buying into that one yet. I may have to put the A6000 24mpx APS sensor up against the A7 24mpx FF sensor with exactly the same lens and than change they magnification on the A6000 by backing up the camera to the same angle of view. Im just not thinking there is any loss of light with this. The same amount of light is hitting the same area of view, that does not change. Why would my effective aperture number change is my real question. The answer given is bigger photo sites , correct. Well is that not compensated in the design of the smaller formats???????????????????????????????????

    I need a better understanding of this because i am not sure i have really seen it in action. Now I am somewhat of APS newbie but if memory serves me well which it does sometimes the same dang sunny 16 rule applied to both MF and 35mm equally. ISO 100 is 1/125th at f16 regardless of system
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    Re: Do the math - focal length and Format demystified

    :dh2:

    :dh2:

    :dh2:


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    Re: Do the math - focal length and Format demystified

    Quote Originally Posted by Shashin View Post
    No one said you cannot correlate DoF among formats, but to get there, it requires additional variables beyond f-number. The video claims that f-number is a measure of DoF. That is not true. Also, this is a very limited statement--true at infinity, not so at short object distances.

    This simple statement, and it is incomplete, is simply an easy way to make comparisons between formats. It is much harder to take this and make universal statements about photography. And it is pretty useless beyond buy a new system. When you take a photograph, do you think in terms of a format you are not using or do you think in terms of the camera you have in your hand?



    So, by this statement, you are saying that smaller sensors may or may not collect less light. Not a useful statement.



    DoF is not dependent on pixel resolution.



    First, pixel area is important in relation to exposure and S/N, not sensor area. Or are you saying you are losing light if you crop you image later? Pixels are the smallest indivisible element of a picture. How many photons one pixel gathers is independent of all the other pixels around it. The fact that a larger sensor has more photon strikes is irrelevant to the image in regards to S/N or the image in itself. It is the photon strikes per pixel.



    First, the industry understands the people don't get how format size changes field of view. They use the fudge of crop factor and equivalent focal length to communicate to consumers. So, when you understand that this is a method to counter people's ignorance, then you would want to question the consumer knowledge, not photo science.

    Focal length is focal length. Sensor size does not change that. That is why the lens description is given in the actual focal length. For some consumer cameras, manufacturer have used equivalent focal lengths (Dimage 7, for example), but there again, it is for consumer ignorance (and you cannot remove the lens). And if you use any equations in photography, plugging in equivalent focal lengths is going to give wrong answers. Focal length is a real optic property independent of field of view.

    And the same with f-number. The f-number given with the lenses is absolutely correct. f-number simply defines the illumination at the image plane. That is it. It is used for exposure.

    What you are proposing is the f-number is a measurement of DoF. That is absolutely false. Folks have a hard enough time with crop factors now, but equivalent DoF given if f-number are really going to confuse these poor saps. How the hell are they going to figure out exposure? Is it the first f-number or the second? Then when you realize that your f-number/DoF scheme is only going to work at infinity and to calculate an effective f-number at some other distance, the whole problem becomes a mess. And you cannot plug in equivalent f-numbers into equations either and get the right result.

    This is what I propose. Why not just use focal length and f-numbers to mean what they actually do mean and let photographers educate themselves instead of inventing crazy schemes?
    get a room!
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    Re: Do the math - focal length and Format demystified

    Johnny - it´s so cosy here....

    for those who don´t want to read the full Zeiss document- here is the important table that we were speaking about before



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    Re: Do the math - focal length and Format demystified

    gotta give stefan his due for keeping cool with all the angst flowing

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    Re: Do the math - focal length and Format demystified

    Quote Originally Posted by johnnygoesdigital View Post
    get a room!

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    Re: Do the math - focal length and Format demystified

    Guy - this is already done correctly in the pro range- as a sample here from Rodenstock´s Digital lens catalogue - does say nearly all you need. Their advantage is that the MF sensor sizes right now do only vary in a narrow range.



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    Re: Do the math - focal length and Format demystified

    Quote Originally Posted by jlm View Post
    gotta give stefan his due for keeping cool with all the angst flowing

    I Agree but everyone needs to keep there cool please. Its a discussion lets treat it like that and not personal. PLEASE

    Thanks as I really don't like the insults and such. If you think someone is wrong or correct than post accordingly.

    I honestly don't like being the peace keeper here folks. Im just pretty laid back and we are not going to die over this one.


    The key here is figuring out what type of system may work best for your style or on a Pro level your clients needs. For the hobbyist and Pros alike its about getting the best bang for the buck and something you enjoy working with. Really end of the day all these systems are crazy good than when I started digital back in 1990. I can't tell you how much better off we are today.
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    Re: Do the math - focal length and Format demystified

    Quote Originally Posted by Guy Mancuso View Post
    Now if they did this if you wanted a 74 degree angle of view in any format than you buy that lens that is in that format system. Easy Peasy.

    I think this is actually a 24mm in FF. But if they created that system a lot of confusion would have been eliminated. Not all but some

    Im still having a issue with loss of light on format change, not sure I am buying into that one yet. I may have to put the A6000 24mpx APS sensor up against the A7 24mpx FF sensor with exactly the same lens and than change they magnification on the A6000 by backing up the camera to the same angle of view. Im just not thinking there is any loss of light with this. The same amount of light is hitting the same area of view, that does not change. Why would my effective aperture number change is my real question. The answer given is bigger photo sites , correct. Well is that not compensated in the design of the smaller formats???????????????????????????????????

    I need a better understanding of this because i am not sure i have really seen it in action. Now I am somewhat of APS newbie but if memory serves me well which it does sometimes the same dang sunny 16 rule applied to both MF and 35mm equally. ISO 100 is 1/125th at f16 regardless of system
    This sensor area/light gathering thing I think is coming from a badly formed idea of information theory. The idea is that a larger sensor is gathering more "information" in terms of total signal. The problems comes that information needs context (not Contax). It does not mean a great deal in terms of what most photographers do--making pleasing images. Images only need, in terms of information, a limited set. Optimizing information will not lead to "better" results as the consumer of the information, the human visual system, does not need it. That is gobbly gook for a nice image actually looks nice and it does not matter what camera it is from.

    And yes, the sunny sixteen rule applied to all formats. I have even used it with 4x5.

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    Re: Do the math - focal length and Format demystified

    "This sensor area/light gathering thing I think is coming from a badly formed idea of information theory."

    So what? Is it really so hard to ignore someone you think is wrong?

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    Re: Do the math - focal length and Format demystified

    Quote Originally Posted by stephengilbert View Post
    "This sensor area/light gathering thing I think is coming from a badly formed idea of information theory."

    So what? Is it really so hard to ignore someone you think is wrong?


    Guy had a question about this. I was just trying to answer it and trying to understand where this idea comes from.

    Why are you even interested in this thread? You have not made any positive contribution and are just sneering at people.

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    Re: Do the math - focal length and Format demystified

    Quote Originally Posted by Guy Mancuso View Post
    One of the biggest problems that was created years ago was using the term focal length and putting a number on it like 24mm lens or 50mm. Back than everything was full frame in photography given the format. Today with APS , m3/4 and so on we are stuck with these multiplication factors to deal with to find the equivalent to FF. What they should have done back in yesteryear was called lenses by there angle of view. Than any lens made in any format change the consumer would go by angle of view. Than all this conversion stuff would have been eliminated. Okay that ship passed a long time ago
    "Everything" certainly wasn't all 35mm. Long before a digital camera existed, I had Minox 8x11mm, Instamatic (26x26mm), half-frame (18x24mm), 35mm film in 24x32/24x36/24x65 mm variants, medium format in 6x4.5/6x6/6x9/6x12 cm variants, large format in 4x5/5x7/8x10/11x14 inch format.

    I never bothered to think of lenses as "focal length==field of view" except when the context of the format was well known. I always thought of lenses as normal, wide, ultra-wide, portrait tele, tele, long tele instead. I never compared DoF scales either ... I looked at the lens scale, or a calculator table, to get a notion of what a given format/lens opening/distance setting would produce in DoF and learned to remember it.

    Of course, I have regularly ignored marketing pap most of my life. And droning video bloggers are surely as bad as marketing pap ... ;-)

    G

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    Re: Do the math - focal length and Format demystified

    Quote Originally Posted by Guy Mancuso View Post
    One of the biggest problems that was created years ago was using the term focal length and putting a number on it like 24mm lens or 50mm. Back than everything was full frame in photography given the format. Today with APS , m3/4 and so on we are stuck with these multiplication factors to deal with to find the equivalent to FF. What they should have done back in yesteryear was called lenses by there angle of view. Than any lens made in any format change the consumer would go by angle of view. Than all this conversion stuff would have been eliminated. Okay that ship passed a long time ago
    Field of view angles are hard to remember. I bet no-one here can pull out of their head what the horizontal, vertical or diagonal angle of view of a 50mm lens on 35mm format is.

    I would have preferred an even simpler system based on magnification. Define normal to be a focal length 1.15 times the format diagonal (to place the normal at the useful convention of a 50mm lens on 24x36mm format). Then:

    ultrawide = less than .55x
    wide = .73x to .62x
    normal = 1x
    portrait tele = 1.5x to 2.5x
    tele = 3.5x to 5x
    long tele = greater than 5x

    That scales, can be applied to any format proportions, and whether it is horizontal, vertical, or diagonal angle of view is irrelevant. You can use either the name mnemonics or the magnification numbers to determine what a lens is giving you.

    It'll never happen, of course.

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    Re: Do the math - focal length and Format demystified

    Useful idea ! I think .... something like this was used back in the 50ies and 60ies and that was certainly not bad !
    By this factor also zooms could be defined very easily.



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    Re: Do the math - focal length and Format demystified

    WOW. You guys must REALLY care about this...
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    Re: Do the math - focal length and Format demystified

    Quote Originally Posted by Guy Mancuso View Post
    Im still having a issue with loss of light on format change, not sure I am buying into that one yet. I may have to put the A6000 24mpx APS sensor up against the A7 24mpx FF sensor with exactly the same lens and than change they magnification on the A6000 by backing up the camera to the same angle of view. Im just not thinking there is any loss of light with this. The same amount of light is hitting the same area of view, that does not change. Why would my effective aperture number change is my real question. The answer given is bigger photo sites , correct. Well is that not compensated in the design of the smaller formats???????????????????????????????????

    I need a better understanding of this because i am not sure i have really seen it in action. Now I am somewhat of APS newbie but if memory serves me well which it does sometimes the same dang sunny 16 rule applied to both MF and 35mm equally. ISO 100 is 1/125th at f16 regardless of system
    The way I understand it from a "real world" perspective is the aperture value (read: ratio) doesn't change but rather the FOV due to the crop sensor only really projecting the inner 2/3 of the lens. I believe you can still use the lens in the same lighting conditions at the same ISO personally to create a similar look to the image. Case in point my 35/1.2 is able to be used in the same lighting conditions at similar apertures on FF or APS-C. On APS-C is obviously gives a "53mm" FOV but the DOF would still be the same DOF a 35mm lens would have on FF or APS-C.

    With that said there's no conspiracy. Larger sensors are capable of more shallow DOF but that's not because of the lenses. That's because of sensor size. Aperture values like stated many times before are a ratio based purely on the lens and is sensor independent. Lens FOV equivalents are just that. The same way people can convert MF lenses by approximately 0.6 for FFMF or 0.8 for cropped MF to get a 35mm "equivalents." They will have more shallow DOF but I guarantee a MF lens with a aperture value of 4.5 can't be used in the same lighting conditions as a Noctilux wide open and handheld just because of a larger sensor.

    Moral of the story aperture values (read: ratios) are constant and independent of sensor size. DOF is not and is dependent on sensor size... Oh and sorry I refuse to Google articles or math equations. I just did an experiment the old fashion way. Manual mode and constant set values.
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    Re: Do the math - focal length and Format demystified

    A lens projects a cone of light to the rear.
    The distance from the rear lens node to that image when focused at infinity equals the lens focal length.

    The intensity of the light at the image plane is a function of the lens aperture.

    The lens does not know or care what if any film or sensor is at the image plane.

    These are just basic laws of physics, unrelated to photography but applicable thereto.

    - Leigh
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    Re: Do the math - focal length and Format demystified

    hmm, based on the video all sensors are approx equal, and hence why the "light gathering" is less on micro four thirds, than it is APS-C, than full frame. But no sensor is made equal, and so it is possible that sensor manufacturers like Sony are able to make smaller sensors perform better in terms of signal to noise, and hence able to have a greater light gathering potential for a particular ISO.
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    Re: Do the math - focal length and Format demystified

    Quote Originally Posted by mazor View Post
    hmm, based on the video all sensors are approx equal, and hence why the "light gathering" is less on micro four thirds, than it is APS-C, than full frame. But no sensor is made equal, and so it is possible that sensor manufacturers like Sony are able to make smaller sensors perform better in terms of signal to noise, and hence able to have a greater light gathering potential for a particular ISO.
    Exactly my thinking as well
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    Re: Do the math - focal length and Format demystified

    My a6000 and A7 where almost identical settings tonight. Was not scientific as I was shooting a gig and not testing but if I was to guess felt like 1/3 of a stop. Now the A6000 LCD is a touch dimmer too. So I would have to go by numbers to be sure
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    Re: Do the math - focal length and Format demystified

    Quote Originally Posted by Guy Mancuso View Post

    Im still having a issue with loss of light on format change, not sure I am buying into that one yet. I may have to put the A6000 24mpx APS sensor up against the A7 24mpx FF sensor with exactly the same lens and than change they magnification on the A6000 by backing up the camera to the same angle of view. Im just not thinking there is any loss of light with this. The same amount of light is hitting the same area of view, that does not change. Why would my effective aperture number change is my real question.
    For the same exposure the light hitting both sensors does have the same intensity.

    Since the big sensor has more surface area but is hit by the same intensity of light it is hit by more total light.

    For FF vs m4/3's it is about 4 times more total light since it has about 4 times more surface area.

    So if you fill your image with the same face and shoot at the same exposure the FF image will have about 4 times the total light to create the face.

    Four times the light equals two stops.

    So, at the identical exposure settings, a FF image has two stops more total light to work with which means two stops less noise.

    That is exactly what I found when I compared my EM5 to my D4.

    You can also test this by shooting a scene then backing up and shooting it again with the same camera and same settings.

    Crop the more distant image and blow it up to equal the size of the close up image. Presto, more noise. Also, more DOF.

    Great photography depends on many things, format least of all.

    -Bill
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    Subscriber Member Georg Baumann's Avatar
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    Re: Do the math - focal length and Format demystified

    I was wondering, in the 4/3 and MFT world, if I remember correctly, they use so called telecentric lenses, right?

    The f number is only considering objects at infinite distance!

    The "Working f number" calculates objects differently (think macro).

    Now this is what a significant manufacturer has to say about it:

    Note that numerical aperture (and F-number) refer to both image and object space, as they can define both the cone angle of incoming and outgoing rays. Usually F-number refers to image space and numerical aperture is more commonly used in object space (incoming rays).
    In macro lenses, like Telecentric Lenses, the F-number parameter loses its meaning as the object is not located at infinity; the working F-number should be used instead. Those two parameters come together in the formula:
    source: Frequently Asked Questions | Opto Engineering*

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    Re: Do the math - focal length and Format demystified

    Nobody seems to mention the circle of confusion, but does not most of DoF discussion boil down to this? And it is not limited to sensors but applies to film as well or first.
    http://http://en.wikipedia.org/wiki/Circle_of_confusion

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    Re: Do the math - focal length and Format demystified

    Guy and all

    the usable base sensitivity of the ready made camera will probably be kept the same (according to the given ISO´s) some can do 50, or 100 or 200 Iso.
    Where the so called Photon count of the sensor- which is one of the real measurements of the quality of this sensor- is somewhat hidden in an electronic amplification to reach that pronounced base level.
    This amplification will be lower on a chip with larger pixels and higher with smaller pixels ("photosites"). Normally such small chips as with MFT or even a Nikon V1 do have smaller pixels thus higher amplification-thus more noise- thus less quality.
    Of course manufacturers have made huge progress the last years, the visible results are quite pleasing - at least when there is enough light. Things change already at low light conditions and noise will be more visible.

    This was also shown in the video. Maybe not with a scientific nomenclature, but with the results, which is what many demand as they do not want to deal with formula and math.....

    I still think this video is quite good.

    Proposal: make a better one and then I hope anyone understands this in a second .....

    Greetings from Germany
    Stefan

    PS.: the ideal sensor would have a photon count of 1, indeed there are some cameras which have such sensors - see e.g. Andors sCMOS cameras for scientific usage.

    http://www.andor.com/scientific-came...s/neo-55-scmos
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    Re: Do the math - focal length and Format demystified

    Quote Originally Posted by mazor View Post
    hmm, based on the video all sensors are approx equal, and hence why the "light gathering" is less on micro four thirds, than it is APS-C, than full frame.
    Then the video is wrong.

    I use exactly the same lens aperture for an exposure on 35mm and on 8x10".

    That's about an 8x range of "sensor" sizes. Absolutely no difference in exposure.

    The same is true on 35mm and MF digital.

    - Leigh

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    Re: Do the math - focal length and Format demystified

    The problem of noise being a product of sensor area, rather than a function of the performance of the pixel is that is hard to find proof of that. Here are four sensors: m4/3, APS, 35mm, 44x33 at ISO 200 and 1600. There is no linear relationship that can be observed. If you want to know what noise a sensor has, just look at the specifications of the pixels.

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    Re: Do the math - focal length and Format demystified

    Quote Originally Posted by Shashin View Post
    If you want to know what noise a sensor has, just look at the specifications of the pixels.
    Part of the problem is that "noise" is the combination of several different error sources.

    Although these are produced by different physical effects at different locations within the device, they all look the same to someone looking at a photo.

    As an example, the real "sensor", being the light-sensitive device, generates noise based on its temperature, assuming that is above absolute zero. This noise is extremely low amplitude.

    The sensor is followed by an amplifier chain that brings the signal level up to a level that can be processed by the microprocessor. This amplifier chain also generates noise based on temperature, but with different characteristics than the noise from the sensor.

    That amplifier chain is also susceptible to environmental electrical noise, and amplifies that just as though it was a signal from the optical sensor. A gross example of this would be a lightning strike, but there are millions of weaker sources in our modern environment.

    The list goes on and on, but I won't bore you further.

    The bottom line is that you're trying to evaluate a very complex set of effects and processes as a single function, which it definitely is not.

    - Leigh

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