On Tue, 17 Nov 1998 07:56:54 -0500, ed romney wrote:

>There is a new lens test chart advertised where you test the lens at
>about 3 1/2 feet. That is a good way of testing enlarger lenses or macro
>lenses but faulted for testing camera lenses. Many of them don't reach
>top sharpness until 8 or 10 feet. The old 1951 NBS and Air Force test
>chart was intended to be used at 26x the focal length. That was fine for
>a 5 inch lens on the older 4 x 5 cameras of the time. The chart would
>then be placed 130 inches away, you see. But with a 50mm lens the chart
>would be only 52 inches away. That is too close. So for my repair
>book I enlarged the NBS chart 2x for modern 35mm cameras. You need to
>observe this precaution too. Particularly note that lenses with
>floating elements such as the 24mm F2 Nikon will do extra well at 26x
>FL whereas lenses like the Nikkon 50mm F1.4 will not test as well as
>this excellent lens should at 26x FL..Best wishes..Ed Romney
>http://www.edromney.com

Good point about lens testing - I've been pratting on about this
for years now on the NG's...! (But does anyone listen? No! ;-)
Many excellent speed, short tele, and zoom lenses are quite
distance-sensitive for optical performance quality, and can
look bad if tested at too close a focus distance - yet these
lenses can perform superbly in "normal" use...