>An easy way to test this would be to scan a dusty negative at
>4000 dpi and then seeing if the dust spots are equally focused
>at the edges as in the center.
Another way would be to deliberately scratch a blank or dud frame. I've
tried this myself when I was concerned about focus on my Nikon. If you
put a scratch edge to edge, you have a really sharp detail to look at for
focus. What I discovered was that I really need to use a tripod more often!
Of course - with slides, the type of slide mount may be significant; some
allow the film to bow more, and some are thicker. Another possible issue
is how quickly you scan; I found with negative strips in the film strip
feeder that they tend to bow more the longer they are in the scanner, heated
by the mechanism. The end frame in a strip may show better focus on one
side than the other. With slides in projectors, I found in the past that
the heat of the projector globe would cause the bow in the film to reverse
- I imagine the heat of a scanner could do that same, and if it happened
*after* the scanner did an autofocus, you have a fuzzy scan.
Just some things to consider, anyhow.
Rob Geraghty email@example.com