But don't forget the final step which is to enlarge the 50mm cropped
area to produce a print of equal size to the 100mm uncropped area. That
means the size of the CoC for the cropped image must be decreased to
account for the additional magnification. It's the decreased CoC
requirement which brings the DoF back into equilibrium despite the
differences in focal length.
Chuck Norcutt
On 11/18/2010 3:11 PM, Bill Pearce wrote:
> Let's remember, before this gets too clouded. A 50 mm lens has the same dof
> as a 100mm lens, if the 50 is cropped to the same coverage area as the 100.
> Therefore, a 50 on FF will have what we consider conventional dof, but the
> same as a 100 on 4/3's, as we have done the cropping in the camera. There's
> nothing magic about either changing sensor sizes or cropping.
>
>
>
> From: usher99@xxxxxxx [mailto:usher99@xxxxxxx]
> Sent: Thursday, November 18, 2010 1:52 PM
> To: olympus@xxxxxxxxxxxxxxxxx
> Subject: Re: [OM] 0.95
>
>
>
> I liked Jeff's points and link---
> Always found this a bit confusing depending how one views the issue of
> DOF and sensor size:
>
> For an equivalent field of view, the FT camera has at least 2X MORE
> depth of field than a full-frame camera would have - when the focus
> distance is significantly less then the hyperfocal distance (but the
> full-frame format need a lens with 2X the focal length to give the same
> view).
>
> If you use the same lens on a FT camera and a full-frame camera and
> crop the full-frame image to give the same view as the digital image,
> the depth of field is IDENTICAL --one of AG's points I think. One
> rarely thinks about the issue that way, I believe.
>
> If you use the same lens on a small-sensor camera and a full-frame
> camera, then shoot from different distances so that the view is the
> same, the FT image will have about 2X MORE DOF then the FF image.
>
> This ignores the mirror box issues, ISO "cheating "at wide apertures in
> some cams and is derived from thin lens assumptions. I have never seen
> a full wave solution form any of today's complex beasties. Nasse who
> wrote the white paper for Zeiss, thinks that whole assumption
> though useful is likely not very accurate. He states the usual tables
> and calculators "should not be taken too seriously." Do some lenses
> appear to or really have more DOF? It is a very difficult experiment
> to design as Dr. Focus has pointed out, but is doable, IMO.
> I suspect some types of aberrations/bokeh/microcontrast will at least
> give the impression of more dof and in an image, impression is reality,
> IMO.
>
> Mike
>
>
> http://www.zeiss.com/c12567a8003b8b6f/embedtitelintern/cln_35_bokeh_en/$file
> /cln35_bokeh_en.pdf
>
>
>
>
>
> You might be remembering two aspects.
>
> Stephen, Ken, etc brought up how a longer focal length has to be used to
> have the same image framing with a larger image size. From
> <http://www.cambridgeincolour.com/tutorials/digital-camera-sensor-size.ht
> <http://www.cambridgeincolour.com/tutorials/digital-camera-sensor-size.ht%0b
> m>
> m>
>
> "As sensor size increases, the depth of field will decrease for a given
> aperture (when filling the frame with a subject of the same size and
> distance). This is because larger sensors require one to get closer to
> their subject, or to use a longer focal length in order to fill the
> frame
> with that subject. This means that one has to use progressively smaller
> aperture sizes in order to maintain the same depth of field on larger
> sensors."
>
>
>
> --
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