Hard as it is to remain serious in this thread, I'll try. :-)
Magnification is one of the keys, and very important. For a while, let's
keep the aperture and circle of confusion effects out of the equation
(make them constant to all the scenarios below). So for this moment,
magnification is our tool.
Zooming out or stepping back would reduce image size, increasing the
perceived DOF.
But that's part of the problem, since we have now a pic a little smaller
than we wanted. So we enlarge said photo back to the desired size, and
we MAY keep the perceived DOF, as long as we don't degrade the image in
the process. Best if we have some megapix stored just in case. Taking
this to a limit, the circle of confusion that was acceptable in the
small image becomes unacceptable in the enlargement.
But there is still another point to consider - viewing distance of the
final, enlarged photo. Looking too close is another way of enlarging the
photo, and there go the perceived DOF and sharpness away. Keep the
distance and the image keeps looking sharp - small, but sharp.
Small sensor P&S cameras use so small images they offer some serious DOF
- offset by other considerations very quickly. As you move up in sensor
size (assuming of course you use a corresponding larger image) the
perceived DOF will drop. Want it back? Small image, to be enlarged later
if the number of pixels remains on our side.
Now, about that light at the end... ;-)
LF
Larry Colen escreveu:
On Tue, Apr 07, 2009 at 09:32:47AM -0300, Luiz Felipe wrote:
You're actually saying if one zoom out (reduce the magnification of the
subject) and crop back to the desired composition the DOF will be
increased, right? So the pic taken with the zoom at 35mm will present
greater DOF than the one taken at 70mm, after you enlarge both to the
same subject size, right?
This is the premise behind point and shoots having greater depth of
field than APS which has greater depth of field than Full Format. Or
conversely if you want to limit DOF at a particular angle of view, you
may need to go to FF.
...so the K20d has greater DOF than the *ist DS, right?
Because you can shoot with a shorter lens and crop, since DOF is based
on focal length squared and CoC as a linear value.
Mind you, if you down res a photo from 2000x3000 pixels to 400x600
then an edge that had been 5 pixels wide is now only 1 pixel wide so
even if DoF can't be changed in post processing, there will be a lot
more lattitude in what you cannot see is out of focus.
I love numbers... :-)
LF
JC OConnell escreveu:
depth of field is determined solely by in camera magnification
and working fstop. So cropping/format is not a factor but changing
lenses from a given distance will affect DOF, likewise moving further
away with the same lens and stopping down more will also both increase
DOF.
JC O'Connell
[email protected]
-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of
Larry Colen
Sent: Monday, April 06, 2009 4:35 PM
To: Pentax-Discuss Mail List
Subject: Trading resolution for depth of field
Perhaps someone has already done the math, or the experimentation, and
can just give me the answers.
Scott's pictures of his Nishiki inspired me to shoot some of my mongrel
legnano. I rode it to lunch today, and on the way back to the office was
getting some shots of it with some lupin by the side of the trail.
I didn't have quite as much depth of field as I'd like, so I decided to
try zooming way out and then just cropping. Smaller sensor, shorter
lens, more depth of field. If the equation is linear, I should get the
same DOF by downresing (downrezzing?) a longer lens over the whole
sensor, as I would using a shorter lens and cropping.
This would also mean that a K20 would have a lot less DOF than my K100
at the same focal length, assuming that they were blown up large enough
that the sensor resolution became a factor.
So, if I'm willing to trade resolution for depth of field, am I better
off using a wider angle lens and cropping (my intuition says yes), or do
I get the same benefit by just combining pixels (which would also reduce
noise) for a larger circle of confusion?
--
Luiz Felipe
luiz.felipe at techmit.com.br
http://techmit.com.br/luizfelipe/
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Luiz Felipe
luiz.felipe at techmit.com.br
http://techmit.com.br/luizfelipe/
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