Depth of field (DOF) does NOT change with sensor size

Discussion in 'Photography Beginners' Forum' started by donny1963, Nov 18, 2018.

  1. donny1963

    donny1963 No longer a newbie, moving up!

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    here is another BS statement i hear all the time and just watched Ken explain this in a video..
    Dept of field does not change with sensor size.

    If you take a 50mm lens and attach it to a Crop sensor camera then also that saame lens then attach it to a Full Frame or Even Medium format camera and your standing in the same postion the DOF will not change they will all be the same.. When people say sure it changes, i laugh and think to myself these are the same people who argue that larger sensors gather more light. Which is not true either..

    Sensors do not work like solar panels LOL

    any way here is the video explaining all this about Depth of field (DOF) does NOT change with sensor size




     
  2. Tim Tucker 2

    Tim Tucker 2 No longer a newbie, moving up!

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    That's what equivalence does for you...

    Although having a TAP video makes me want to run away, as quickly as possible, you have to fully understand the the relationships between sensor size, DOF, fov, focal length and exposure.

    These are so intrinsically linked that if you change one then another will change by a proportional amount, and if you hold certain parameters constant then others will stay constant.

    For instance if you adjust aperture then exposure changes unless you make an equal change in shutter speed where it doesn't.

    The thing is that *if* you hold the total amount of light falling on a sensor and fov as constant then DOF is also constant but exposure changes, if you take *equivalent* shots with different sensors in that the total amount of light and the fov is equal in both shots then both will also have the same DOF but they will have different exposures. If you hold exposure constant then the *equivalent* shots will have different DOFs.

    The thing is that by stipulating the conditions in which to compare the noise characteristics of different sensors then you have to set conditions to cancel out differences between them. In other words you stipulate that comparable photos must have the same total light and fov then they *must* also have the same DOF. It is then a little silly to state that DOF if the same between all sensors when you first set the parameters so it must be.

    Basically by cancelling out sensor size you also cancel out focal length, but then exposure must vary between *equivalent* shots because you deal in actual aperture diameter instead of f-stop. If exposure is constant then DOF varies because you deal with f-stop which is proportional to focal length.

    The calculations are over-simplified and are not fully correct anyway. The system works and allows you a different understanding of the relationships, but only if the relationships remain proportional. DOF is only proportional at portrait distances but not at landscape distances. It only changes in a proportional manner up to the point where infinity is said to be within the DOF, (hyper-focal distance to infinity), then decreasing aperture only increases DOF towards the camera, and it is no longer proportional to aperture. This allows you to take landscape images with smaller sensors that have essentially the same DOF without *equivalent* settings. The system doesn't fully explain these relationships, it is just a special case that only exists in theory and only exists because you stipulate as a condition of proving it that it must, (lens performance is linked to f-stop rather than aperture diameter and therefore focal length can't be cancelled from the equation because we arrive at the situation where an aberration loaded image at f1.4 is equivalent to one shot at f4, by proving focal length is irrelevant we must first ignore where it is relevant).

    I find that it does allow you a more complete understanding of the relationships between the fundamental controls of the camera, but is also used as a sort of *geek speak* by those who want to create the illusion that they understand photography and digital better than anybody else, rather than my preferred method of using understanding to create better images. It becomes a sort of elitist club with silly handshakes and jargon...
     
    Last edited: Nov 18, 2018
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  3. Overread

    Overread has a hat around here somewhere Staff Member Supporting Member

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    If depth of field doesn't change with sensor size why is it when I compare medium format photos to mobile phone photos the depths of field are VASTLY different even at the same settings?

    Also why would most (if not nearly all) calculations for depth of field require sensor size in the equation if it has no effect. Since sensor/film size affects the circle of confusion value
     
  4. Vtec44

    Vtec44 Been spending a lot of time on here!

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    Pretty much... :D

    I mean understanding the technology is great but how do you put it in practical uses, in this case create beautiful images? In many cases, there are numerous people who are great at repeating the information but have no real knowledge practical application of the technology. I'm not referring to anyone in particular just a general observation.
     
  5. petrochemist

    petrochemist TPF junkie!

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    The amount of blur on the sensor doesn't change, but AFAIK no one actually views their pictures directly on the sensor. When you output images from small sensors you magnify them more so even without changing position or focal length DOF will change.
    It also changes depending on how the images are viewed so the simplistic calculators that use a fixed circle of confusion for each sensor are not a great deal of help if they're not set up using the conditions your prints are viewed at. Pixel peepers need much sharper images (smaller coc) than those downsizing for the web or making the old 6x4 size prints.
     
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  6. Tim Tucker 2

    Tim Tucker 2 No longer a newbie, moving up!

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    LOL, yes indeed. Especially:

    This highlights the basic contradiction and mindset I've always had a problem with and have never been able to communicate to *equivalentoligists*. That the act of producing equivalent photographs requires you to have a reference point of another photograph to be equivalent to. Basically it's the science of being able to copy not create.
     
  7. Tim Tucker 2

    Tim Tucker 2 No longer a newbie, moving up!

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    LOL, now having watched the video because a little light entertainment is always good on a Sunday morning, I am now in a more jovial mood.

    There are so many basic mis-conceptions and mistakes, that the amount of hysterical laughing and giggling are about the only relevant things in the video. By rubbishing others and ridiculing viewers for blindly following what they say he is quite categorically asking you to do the same here. It's a complete waste of time.

    Images are our human perception of them when we view the *finished* print. The idea that they are fixed on a sensor by the action of a lens and that if a lens is the same then the image therefore *must also be* is completely false. There are so many things that are different, (fov, magnification etc...), that the only logical conclusion is that your perception of the finished image must be different, not the same.
     
    Last edited: Nov 18, 2018
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  8. AlanKlein

    AlanKlein No longer a newbie, moving up!

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    I put this example (2x crop sensor) together to explain it to me a few years ago. To me it seems that the smaller sensor (2x crop sensor) acts like a telephoto lens capturing a smaller part of the picture, half the FF sensor would do. That decreases the depth of field just like doubling the lens would do on a FF camera sensor. If you halved the lens to a wide angle, the DOF would be the same.
    Crop factor illustration.jpg
     
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  9. Ysarex

    Ysarex Been spending a lot of time on here!

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    Wrong.

    Proof:

    dof.jpg

    (Just for the sake of maintaining some semblance of rationality, LOL, assume the lens above is a Hassleblad 50mm Distagon.)

    Wrong.

    You are confusing exposure with light gathered. You made that mistake earlier and were corrected: So Who Believes that Full Frame Camera's Gather More Light Then APSC


    A blathering idiot.

    Joe
     
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  10. Ysarex

    Ysarex Been spending a lot of time on here!

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    I'd suggest saving it for late some Saturday night and start drinking before you start the video as it's not very long.

    Joe
     
  11. Braineack

    Braineack Been spending a lot of time on here!

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    [
    Go outside, actually do this test, and then see if you keep laughing...

    you literally have not done this test yourself, and do not understand the science behind it, yet youll sit here and laugh at the people who actually understand and know why the DOF does change.

    SAD.
     
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  12. Braineack

    Braineack Been spending a lot of time on here!

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    you left out a few choice adjectives.
     

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