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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