Hi Klaus, just wondering what is the lens to test chart distance in your typical lens testings. I would assume the lens are focused at its short range in order to fit all the testings indoor. In real world use, I find the sharpness of a lens varies greatly depending on focus distance. For example, I have a tele zoom lens that delivery excellent result at close range, but simply falls apart when focus to infinite. I understand that atmospheric haze plays a unpredictable rule here, would that be useful to include some distance test shot in lens test as well?
03-15-2012, 11:40 PM
(This post was last modified: 03-15-2012, 11:46 PM by Brightcolours.)
[quote name='jiamflash' timestamp='1331837684' post='16739']
Hi Klaus, just wondering what is the lens to test chart distance in your typical lens testings. I would assume the lens are focused at its short range in order to fit all the testings indoor. In real world use, I find the sharpness of a lens varies greatly depending on focus distance. For example, I have a tele zoom lens that delivery excellent result at close range, but simply falls apart when focus to infinite. I understand that atmospheric haze plays a unpredictable rule here, would that be useful to include some distance test shot in lens test as well?
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All lenses are tested at a defined distance according to their focal length. It has to do with the test chart itself. For the tests, the measuring software needs to know how big the target is... so for tele lenses, the distance to the test chart must be a LOT bigger than the distance to the test chart for a wide angle lens.
So, it depends on the test chart design. I believe the distance is 51x the focal length.
So that then means that for a 300mm focal length, the distance from sensor to chart must be set at 15300mm, or 15.3m.
And then for a 24mm focal length, the distance from sensor to chart should be set at 1224mm or 1.22m.
.This is standard procedure for testing websites like photozone, lenstip, SLRgear.. and magazines like foto magazin and colorfoto.
This also explains why marco lenses never are tested at macro distances.
The object magnification is about 1:30 for full format and 1:50 for APS-C.
So this is neither a macro nor an infinity scenario but something in between.
When looking at the focus distance scale of your lens that's roughly at 2/3 to 3/4 of the scale (towards infinity).
