Agreed but, except for the comment about format differences in
diffraction limits, it seems to me a distinction without a difference.
Chuck Norcutt
On 11/19/2010 3:00 AM, Jeff Keller wrote:
> Not really equilibrium ...
>
> Another presentation is at:
> http://photo.net/learn/optics/dofdigital/
> Using simple formulas and calculated coc on the same size print the
> management conclusion is: "So the bottom line - and all you really need to
> know - is that DOF is inversely proportional to format size."
>
> Which is really the same (?) as "If the focal length then changes by a
> factor determined by the image format, we only have to multiply the f-number
> by the same factor. Then the quotient, that is to say the entrance pupil,
> has the same value again and we have the same depth of field relationships."
>> From Mike's Zeiss link. This was using the "If the acceptable blurriness is
> supposed to be the same with these different cameras, it means that the
> ratio of the object field diagonal and the "object-side circle of confusion"
> should be the same."
>
> But keep in mind the conclusion in the Cambridge In Color link "In other
> words, if one were to use the smallest aperture before diffraction became
> significant, all sensor sizes would produce the same depth of field-- even
> though the diffraction limited aperture will be different." (ideal lenses
> assumed)
>
> When switching between formats four-thirds seems to have little need for
> f11+ while 4x5 seems to have little use for f8- (many modern large format
> lenses diffraction limit by f11 or sooner so I'm not talking about non-ideal
> lens affects)
>
> Jeff Keller
>
> -----Original Message-----
> From: Chuck Norcutt [mailto:chucknorcutt@xxxxxxxxxxxxxxxx]
> Sent: Thursday, November 18, 2010 1:17 PM
> To: Olympus Camera Discussion
> Subject: Re: [OM] 0.95
>
> 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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