On 8/5/2010 5:14 PM, Chuck Norcutt wrote:
> There might be perfectly fine reasons to get a 7D vs 5D Mk II but depth of
> field for landscape shots will not be one of them.
Weeelll, I'm not so sure. What's a "landscape" shot? Yes, I do shoot lots of
what I would call landscapes, natural views
at some distance from the camera. I also shoot a lot of close-up/macros of
flowers, etc. and a fair number of full zoom
shots of distant objects and some what you might call medium-close shots.
> Although shorter focal lengths lead to greater depth of field, the larger
> magnification required from the smaller sensor leads to lesser depth of field.
In the intent to be brief, that seems to me clumsily worded, seemingly
contradicting itself, but correct in intent. Then
again, bringing in COCs and more words doesn't sound good ...
> Diffraction also places limits and tends to be the equalizer.
I don't think this is as simple as it sounds. With deep, 3D subjects, the trade
off may be quite different than one
would get from theory - and than with shallow subjects. I did a series of shots
of a clump of fleabane a few years ago
on 35mm film using the 135/4.5 lens, because it could be stopped down so far.
With this range of flowers and foliage
over great depth, it wasn't until I hit f45 that diffraction softening overcame
improvement in overall apparent
sharpness from increased DOF.
I also wonder if there aren't variations from simple lens theory with different
lens designs.
> On a 7D with its 18MP 1.6X sensor you are limited to an aperture of
> approximately f/6.3 to maintain full resolution before diffraction sets in.
> On a 5D Mk II with its 21MP full frame sensor you can use
> approximately f/10 before diffraction starts rearing its head.
I think I recall you quoting f11 for the 5D. Yet I have many close-up shots
with the 5D where f16 gives better overall
sharpness. I'm almost convinced, pending some more shootin' and pixel peepin',
that f22 may be ideal for max overall
DOF/sharpness with 5D and my Tammy 28-300 at/near the long end and close focus.
I'm not saying you are wrong in concept,
but like AG, that empirical results trump theory for me. That is, of course, a
very complicated lens design.
> If you use a 15mm lens on a 7D at f/6.3 and a 24mm lens on a 5D Mk II at f/10
> both have exactly (well, within rounding error) the same hyperfocal distance
> of 5.7 feet and nearest focus of half that.
Assuming for the moment that the other factors I've mentioned aren't at play, I
am often fighting with inadequate light
to optimize exposure and DOF factors. Obviously, almost 1.5 stops faster for
the same DOF can be an advantage all by itself.
> Obviously, DOF for other distances will be the same as well. Unless the 15mm
> lens on the 7D is exceptional I think the advantage goes to the 5D Mk II.
> It's much larger pixels mean the lens doesn't have to be as precise. But the
> pixel density on even the 5D Mk II will be a challenge for lots of glass and
> the 7D very much more so.
Yup, I been thinkin' on that problem, as well. I sure don't see where I really
need 18 MP, let alone 21, but the
7Djr,with all the other good stuff and the best 12MP sensor system they could
make doesn't exist.
Just thinkin', not buying, so far.
Apostrophe Moose
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