// >checking image in VF PROCEDURE FOR LENS CHECKING--
Well, enough of all this blather - on to some ways you can quickly
and easily determine
I'm still thinking about that article I've been working on on
practical and easy lens checking, but it hasn't been easy to
write it, so it isn't here yet. But, maybe this should be it:
Since your lens is not a zoom, and has no floating elements,
it is practical to check it out using a minimum of film. I
would check it by taking a vertical photo (with the shutter
release end of the camera up) of a detailed, distant scene,
with the detail at the top of the frame. Then, carefully not
touching the focus ring, turn the camera over, and repeat the
photo (both should be shot wide open). If you feel unsure of
your focusing accuracy, refocus and repeat what you did a few
times. Then shoot the same target at f5.6 and f11 (one frame
each is fine). Develop the film (leave it uncut and/or mounted),
and examine it with a good 10X magnifier. In the pairs you first
shot, you have the same subject in two frames, but just across
the frame lines, where it is easy to compare. Check first the
centers of the edges of the frame pairs (where exactly the same
subject appears). It should be equally sharp and detailed in both
photos. Next, check the opposite corners along the adjacent frame
lines (which also have the same subject material), which should
also be equal in sharpness). If the lens passes this check, it is
probably well-aligned and not affected by any major optical
manufacturing flaw. Use the f5.6 and f11 frames as references to
see how well the lens can perform, and how well it performs wide-open
compared with optimum apertures (this is not for checking if the lens
is up to par - the wide-open checks tell you that - only if you are
satisfied with this particular lens design wide-open). Many good
teles perform badly at minimum focus (not a flaw, but a compromise..),
but checking this is difficult (and is probably best done with photos
of standard subjects taken with the lens wide-open at minimum focus -
then checking the in-focus parts with a magnifier to see if they are
sufficiently sharp for you. If your camera has very fast shutter
speeds, using a fast film with the camera hand-held works well for
this kind of lens checking. Uh, and don't get too caught up in
lens checking - it is a DISEASE, I tell you, a DISEASE!!!!!
Once acquired, it is very hard to get rid of it (just like reading
and writing posts on the 'net....!:<).