Ali Shah wrote:
> Does the camera's sensor have an affect on DOF? Say
> you take a photo in which you want good DOF using an
> Olympus Digital lens on an E-series body. Take the
> same photo (using the same exact settings) with a
> N*kon or C*non dslr using their respective lenses.
> Will the photo be more crisp and sharper from end to
> end with the N*kon or C*non because of the better
> sensor?
When I read this, I groaned. Perfectly legitimate question or questions,
but about one of the most complex and hardest to explain aspects of
photography.
With any luck, you have now received plenty of references and
explanations of the theory of DOF.
----------- Those with any form of limited attention span may skip to
the bottom - if yo don't want to know how complicated this all is. :-)
I'd like to say something about the other questions that seem implicit
in your questions. As Chuck so clearly and simply described, there is
only one distance from the camera at which objects are in perfect focus,
and DOF is simly a measure of how far from that distance one may go and
still have the resulting image APPEAR to be in focus.
The other question that interacts with your question about "crisp and
sharper", is how crisp and sharp is the image of the part of the subject
that is exactly at the focal plane? The sharper the image, i.e., how
close to a perfect, dimensionless point is the image of the star in
Chuck's example, the better the apparent sharpness will be throughout a
given DOF range.
The DOF tables assume a perfect lens, which is not what we are working
with, and a perfect film/sensor system, which is also not the case. So
before even leaving perfect focus, the star image is already a blob with
less than perfectly sharp edges, almost certainly slightly asymmetrical
and with the different colors focusing at ever so slightly different
distances from the lens. All of these effects diminish apparent
sharpness, which is, in itself, a complex and not fully defined thing.
So, as to one aspect of your question about Oly vs. N and C, one really
has to ask which lens you are using and which models of N and C and
which lenses you might be using.
Oly's ZD lenses are generally quite good and, at any given level of
price/target user, at least as good as those of the others, and probably
better at the low end than the competition. So one answer is that, given
lenses from the same quality tier within each manufacturer's line, you
won't gain anything from switching due to lens quality.
Another confounding factor is diffraction as the lens aperture gets
smaller. If it weren't for the same phenomenon of optical physics that
makes pinhole cameras work, you could just stop waaay down, and get
everything in focus on stationary subjects like your ship.
Unfortunately, apertures below a certain size start to lower the
sharpness of the lens due to diffraction of light along the edge of the
aperture. You may have noticed that the lenses for smaller sensor
cameras stop down less far than those for 35 mm film/sensors. That's
because of this limit.
The next issue is how well the various sensor systems work. The E-500 is
a decent, but not outstanding sensor system now a few years behind the
leading edge. ONe of the things reviewers talk about is "pixel level
sharpness". Imagine again Chuck's pinpoint image of a star, this time
hitting only one pixel of the sensor. Ideally, the resulting image
should have one bright pixel surrounded by black pixels. In practice,
this isn't what happens. For physical design, optical and electronic
reasons, their are reasons that the brightness 'leaks' into immediately
surrounding pixels, causing a result sort of like being slightly out of
the focal plane due to DOF issues.
Current N and C APS sensor size camera bodies have less of this effect
than the E-500. So, given equal quality lenses and good technique to
minimize blur caused by inaccurate focus, camera and subject vibration &
movement, and a large apparent image size, whether maginfied via large
print, considerable cropping or pixel peeping, it is likely that an
image from the C or N camera will have somehwat sharper appearing images
with slightly better perceived DOF than the E-500.
Next up is image processing. Apparent sharpness is some difficult to
define combination of resolution, contrast, saturation, local
contrast/accutance and who knows what else. How the image is processed
has a considerable effect on how sharp it looks, as opposed to how many
lines of a test pattern it can resolve. So a further question is how the
camera image parameters are set and what post processing is done.
---------------------
OK, have I made it clear that this question or questions are really
highly complex, and essentially unanswerable without empirical testing?
So there is no clear, simple answer in any absolute sense.
However, if your question, as I suspect, is more or less "If I dump this
Oly and buy a C or N (As all these folks around me say I must to get
good images.), will my problems with getting really great, deep DOF go
away?" - the answer is no.
In fact, your example image is really an exceptional example of great
DOF put to good use. Post processing can greatly increase the apparent
DOF, both far and near.
http://www.moosemystic.net/Gallery/Others/AliShah/MarineStar.htm
> Is this because the sensor absorbs more light?
>
I actually have no idea what you are talking about here, the sensors
will all "absorb" the same amount of light. I can say with assurance
that it has nothing to do with the question(s) you asked.
Moose
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