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Thread: A question about how DOF relates to sensor size.

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    A question about how DOF relates to sensor size.

    I started wondering about maximum possible DOF after seeing some images in a book with garden photos. The DOF where amazing! That started me wondering; given a camera position and a target photo angel,what is the optimal way to achieve good DOF?

    lets say you have 2 cameras,both with (say) 20mPixel sensors. One camera has a big sensor the other has a smaller sensor.
    Both cameras have "perfect" diffraction limited lenses that view the same angle.
    Both cameras are to be used at the same position. The f-stop is set to generate maximum DOF while avoiding diffractions on both lenses.

    Which will give the image with best DOF?

    As I see it it must be the full-frame set up since you can use a smaller f-stop number before diffraction sets in. This point I'm uncertain about,tho.

    Is this correct?

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    Re: A question about how DOF relates to sensor size.


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    Re: A question about how DOF relates to sensor size.

    Hi Pesa,

    "It's complicated". Full Frame cameras have tighter DoF, but diffraction kicks in at smaller apertures.

    At the end of the day though, diffraction isn't usually a big real - in many cases people would get a far better result simply by applying correct sharpening; I have many 22 x 44" canvas prints hanging on walls that were where shot at F22 or even F32, and diffraction wasn't an issue.

    In practice, the best approach is probably (well what I do anyway) to calculate the depth of field and hyperfocal distance that's appropriate for the scene (there's a great iPhone App for that if you happen to have an iPhone).

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    Re: A question about how DOF relates to sensor size.

    Quote Originally Posted by Colin Southern View Post
    Hi Pesa,

    "It's complicated". Full Frame cameras have tighter DoF, but diffraction kicks in at smaller apertures.

    At the end of the day though, diffraction isn't usually a big real - in many cases people would get a far better result simply by applying correct sharpening; I have many 22 x 44" canvas prints hanging on walls that were where shot at F22 or even F32, and diffraction wasn't an issue.

    In practice, the best approach is probably (well what I do anyway) to calculate the depth of field and hyperfocal distance that's appropriate for the scene (there's a great iPhone App for that if you happen to have an iPhone).
    Thanks for the replies, I allready read the article about sensor size.
    Colin,the question might be complicated to "solve" but is the "solution" ? I mean, my theoretical experiment is set up so it CANT (?) generate more than one of two outcomes; DOF is the same or it isnt... Or what am I missing here?

    About hyperfocal distance and DOF, if you do this calculations for the 2 setups I wrote about,would it generate the same result for same size prints from the 2 setups I used as an example?
    BTW, whats the name of iPhone app? I'm the proud owner of one :-)

    About the images you took with F22 or F32, was that with a medium format camera?
    And thanks a million for your other reply where you offered help with printing on an epson3800. I will definitely take you up on that!
    Cheers
    Per Sabelström

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    Re: A question about how DOF relates to sensor size.

    Quote Originally Posted by pesa View Post
    Thanks for the replies, I allready read the article about sensor size.
    Colin,the question might be complicated to "solve" but is the "solution" ? I mean, my theoretical experiment is set up so it CANT (?) generate more than one of two outcomes; DOF is the same or it isnt... Or what am I missing here?
    Hi Per,

    To be honest, I'm not strong in this area - but it's right up Sean's ("McQ") alley. But as I see it, DoF calculations don't normaly over-lap with diffraction calculations ie "DoF" and "Diffraction" are different beasts.

    About hyperfocal distance and DOF, if you do this calculations for the 2 setups I wrote about,would it generate the same result for same size prints from the 2 setups I used as an example?
    No idea - it's 2:33am here - so it's a bit late for me to be thinking about such things!

    BTW, whats the name of iPhone app? I'm the proud owner of one :-)
    "Simple DoF"

    About the images you took with F22 or F32, was that with a medium format camera?
    No - I use a Canon 1Ds3.

    And thanks a million for your other reply where you offered help with printing on an epson3800. I will definitely take you up on that!
    Cheers
    Per Sabelström
    No worries

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    Re: A question about how DOF relates to sensor size.

    Quote Originally Posted by pesa View Post
    I started wondering about maximum possible DOF after seeing some images in a book with garden photos. The DOF where amazing! That started me wondering; given a camera position and a target photo [angle], what is the optimal way to achieve good DOF?
    Just limiting your question to the quote above and using a DSLR – the answer nearly always will be to use a TS-E lens.

    It is likely those Garden Photos were taken with View or Field Camera which has Camera Movements.

    Those Camera Movements can be imitated somewhat when using the Canon TS-E range of lenses.

    WW

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    Re: A question about how DOF relates to sensor size.

    Hi Per,

    I agree 100% with William W on his view of the original cause of the discussion.

    But getting into comparisons between cameras with different sensor sizes ...

    It is my understanding/belief that the crop factor (cf) figure used to multiply a small sensor camera's lens focal length to give you the equivalent focal length of a FF/35mm camera must also be applied to the quoted apertures if you wish to obtain the same DoF comparability.

    This is why, at say "f8"; FF cameras appear to give less DoF than popular DX format DSLR (cf 1.5/1.6) and way less than bridge/compact cameras (which typically have crop factors between 4.5 and 6) - in reality the aperture (for DoF purposes) is not the same. The f8 figure is correct for the given focal length of each lens, which is of course different for the same field of view.

    Cheers,
    Last edited by Dave Humphries; 30th November 2009 at 01:23 PM. Reason: added 'comparability' and re-worded 2nd para for clarity

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    Re: A question about how DOF relates to sensor size.

    Quote Originally Posted by pesa View Post
    lets say you have 2 cameras,both with (say) 20mPixel sensors. One camera has a big sensor the other has a smaller sensor.
    Both cameras have "perfect" diffraction limited lenses that view the same angle.
    Both cameras are to be used at the same position. The f-stop is set to generate maximum DOF while avoiding diffractions on both lenses.

    Which will give the image with best DOF?

    As I see it it must be the full-frame set up since you can use a smaller f-stop number before diffraction sets in. This point I'm uncertain about,tho.

    Is this correct?
    The reason I avoided this part of the question is, in reality you can't have it both ways.

    If we are to have "perfect" diffraction limited lenses in this theoretical test, then, are we also to assume that the Apertures can move to numbers like F/128? , for example . . .

    BUT: if you loosen the parameters of the question a little and make it a general statement, with a few assumptions . . . it kind of evens out, if all the gear is of an equal capacity.

    If you have an APS-C camera then you "get" about 1 extra stop of DoF from it, compared to a 135 format (e.g. 50D to 5D).

    What I mean is: you get in a certain shooting scenario a DoF at F/8 on the 50D . . . to get the same DoF (for that same FoV scenario) you have to be at around F/11 on the 5D.

    Similarly moving from a 5D to a 645 format - you need about F/16 for the same DoF . . .

    But the Diffraction Aficionados will wax lyrical about the Diffraction "kicking in" a bit later with the larger formats - usually about one stop later for any given scenario . . .

    And the larger format lenses usually have smaller minimum Apertures, too.

    You could spend years finding evidence to argue for both sides of the equation – and if you are keeping it totally theoretical, then we would all need to agree on a suitable CoC in the first place – which could take a long time, just in itself

    So to answer your question it is "Swings and Roundabouts" IMO, they will be about similar for practical purposes, looking at a 10 x 8 print at arms length of images shot around F/8 to F/11 on a small format (e.g. 50D) to those at F/11 to F/16 from a larger format camera (e.g. 5DmkII).

    WW

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