Just to put a quantitative spin on this, the physical size of the Airy disc
(the diffraction spot produced by a point source) is directly related to
focal ratio. Any lens at f/22 will produce a diffraction spot 27 um in
diameter. Any lens at f/8 will produce a diffraction spot 11 um in diameter.
Any lens at f/5 will produce a diffraction spot 7 um in diameters.
Most digital cameras these days have pixel sizes in the range of 5-6 um.
What that means is that if you use the lens any slower than f/4 you are
losing resolution to diffraction effects. The lens needs to be operated
faster than f/4 in order for the diffraction and the pixels to be well
matched. Of course, you have to offset that against the fact that as the
focal ratio gets smaller, aberrations- especially off-axis aberrations- get
more severe. That's the idea behind the rule-of-thumb that optimum sharpness
is usually seen a stop or two below wide open.
Chris
*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
----- Original Message -----
From: "Dark Matter" <[email protected]>
To: "Meteorites USA" <[email protected]>
Cc: "Meteorite-list" <[email protected]>
Sent: Wednesday, January 27, 2010 12:49 PM
Subject: Re: [meteorite-list] Meteorite Photography (Must read!)
Sorry, but it won't. The measures are small, but the optical physics are
real.
http://www.kenrockwell.com/nikon/50-comparison/f-stops.htm
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