Perhaps the silver lining here is an end to the pixel-count war, but I
doubt it.
Charlie
On Fri, Nov 21, 2008 at 8:55 AM, Chuck Norcutt <
chucknorcutt@xxxxxxxxxxxxxxxx> wrote:
> In a really long and very technical article from Luminous Landscape
> titled "Do Sensors "Outresolve" Lenses?" the cut-to-the-chase answer in
> in many cases is... yes. The reason is the diffraction limits of lenses
> at various apertures. You can read the entire, nerdy article here
> <http://www.luminous-landscape.com/tutorials/resolution.shtml> or just
> skip to the conclusions which can be found in table 3 near the end.
>
> The table lists different sized sensors from four thirds to medium
> format and, under each format, three different wave lengths of light
> ranging from red to blue with green-yellow light in the center column at
> 0.55 microns wave length. Down the left side of the table are various
> apertures. The larger the aperture the less the diffraction (and
> ignoring other pesky optical problems) the greater the resolving power.
> The data in the table are the maximum number of megapixels that can be
> resolved with that sized sensor, wave length and aperture... and this is
> key... using a perfect, diffraction limited lens. Since none of us own
> any of those the implication is that our real world results will be
> somewhat less than the theoretical maximum.
>
> Since green-yellow at 0.55 microns is where we see best that's a good
> color to choose. The implications then are as follows.
>
> If, like me, you own a 12.7 MP Canon 5D you can scan down the table for
> 35mm sized sensors under 0.55 microns and see that the maximum
> theoretical resolution at f/11 is 16 MP. Since that's for a perfect
> lens, in all probability my real world lenses won't do that well but
> maybe I'm still OK at 12.7 MP at f/11. But going to f/16 is a no-no for
> best resolution since the theoretical limit drops to 7 MP at f/16.
>
> If you own a camera with an APS-C size sensor (most of the Canon, Nikon,
> Pentax, Minolta/Sony DSLR market) at f/11 the theoretical limit is 7 MP.
> You have to limit the aperture to f/8 in order to reach a theoretical
> limit of 13 MP which will maybe cover those 10-12 PM sensors with real
> world lenses. Even a Canon 20D's 8 MP sensor isn't fully resolved at f/11.
>
> And finally we have the four thirds sensor where the pixels are getting
> even smaller. The Olympus E-1 at 5 MP is OK up to f/8 but for newer
> cameras like the 10 MP E-3 you should be limiting lens aperture to f/5.6
> for maximum resolution... assuming your lens performs well at f/5.6.
>
> Remember the Olympus exec's question about using OM lenses on the newer
> four thirds cameras: "Why you want to use old lens on new camera?" If
> he had explained about resolution limits and that many 35mm lenses
> perform best at f/8 or f/11 we, perhaps, might have understood better.
>
> Of course, resolution is hardly the only characteristic of a good lens
> but when you've got that camera mounted on a tripod and shooting some
> landscape or architectural subject for maximum detail remember this
> advice on how to set (limit) the aperture.
>
> Chuck Norcutt
> --
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