...should have known better, shouldn't I? :-)
Real world present hard limits to what kind of enlargement we make from
film or digital alike. I don't take pics thinking of wall size
enlargements to be viewed from 4 inches. I compromise.
Thinking of DOF alone I'd be using the smallest possible sensor, matched
to the smallest focal lenght or staying as far as possible from my
subjects. But then, there are other considerations.
If I could build such sensor bypassing all the other issues related to
sensor size, and was able to produce a really perfect lens free of
distortions and with unlimited resolution, so my camera could offer that
almost unlimited DOF, would you say the limit to my circle of
confusion would be the pixel?
...out of curiosity alone, since I'm rather real, and despite the
unbelievable fun this thread gave me and my co-workers, this should be
my last post to the matter.
LF (trying to get a beautiful brunette to some DOF experiments...)
JC OConnell escreveu:
The problem with this post below is the word "perceived".
The REAL DOF increases with lower magnification, not the
perceived DOF. If you could build a high quality tiny
sensor and had a real short FL lens of unlimited resolution,
you would end up with a camera with immense DOF capability,
EVEN WITH LARGE PRINTS MADE. The viewing angles and print
sizes dont matter. Its the in-camera maginification that
makes the difference, a REAL difference.
JC O'Connell
[email protected]
-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of
Luiz Felipe
Sent: Tuesday, April 07, 2009 5:55 PM
To: Pentax-Discuss Mail List
Subject: Re: Trading resolution for depth of field
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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