tsig
a carbon based life-form
- Joined
- Nov 25, 2005
- Messages
- 39,049
All I see are furry, blurry photos. You are seeing things that are beyond the limit of resolution.
"One of these laws defines the resolution limit of any optical system, any camera lens, even a perfect one with absolutely no lens errors. ......So, even a perfect lens with no lens errors is limited in its resolution! (Such a perfect lens does not exist. Even the most sophisticated lenses on this planet, the Carl Zeiss S-Planar lenses for the semiconductor industry are only approximations to the perfect lens, although very close ones.) Thus the term "diffraction-limited" has become the synonym for lenses that are so good their only per-formance limit is the law of diffraction. According to this law no camera lens used in photography, still or motion, can produce resolutions higher than given in the following table (Approximate, rounded off values for white light spectrum of even energy distribution. In unevenly distributed spectra of gas discharge light sources somewhat higher resolutions may be achieved.)
f-no......................resolution
.............................(line pairs per millimeter)
.45.............................35
.32.............................50
.22.............................70
.16...........................100
.11...........................140
...8...........................200
5.6...........................280
...4...........................400
2.8...........................560
In practical photography other limitations of resolution occur, too. The existing depth-of-field concepts, for example, lead to a limit at 30 line pairs per millimeter, simply because they assume that the image of a sharp point may be considered sharp as long as the unsharp disc it actually is (called the "circle of confusion") grows no larger than 1/1000th of the focal length of the respective standard lens. In 35 mm photography only 1/1500th is allowed. 1/1500 th of the 50 mm standard focal length equals 1/30th mm. So 30 fit into one mm, which means, we are talking 30 line pairs per millimeter (CLN 1 has more details in "Depth of Field – An Insider's Look Behind The Scenes", an article that meanwhile has been reprinted in many publications around the world). This is about the same limit set by diffraction for f/45 which was an aperture setting quite popular with 5 x 7 inch large format photography, producing images that can be viewed without any subsequent magnification.
"(Camera Lens News No. 2, fall 1997)
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