4000tf, sometimes misses focus?

[Harald]

I have never come to grips as to why ArtixScan 4000tf sometimes misses focus. If I scan it again, it may be ok, but you can never be sure. Since I scan in batch, it is VERY annoying when it misses focus, since I don't want to check sharpness immediately, but rather much later on a bunch of images, when it is too late to rescan.

I wonder if someone has found anything one can do to make sure this never happens?
(Note: the media is slides, pretty flat, so glass mount is normally not needed. And I always scan in batch.)

[LSI_Muenier]

Dear Harald,

do you see anything in common between those slides for which the focus misses? There must exist some "edges" / contrasty areas, so that the focussing procedure in the scanner has something to look at.

Best regards
Martin

[Harald]

Not really, it is just plain VERY lousy at focusing! The worst are dense slides, but it can happen to any slide, and very frequently I have to try 2 or 3 times before I get a scan where I can see the grains, and where the dirt is not just fuzzy.

There is only one single non-movable point it attempts to focus, and in any slide, that point may happen to be in a featureless spot. However, since it is mostly Sensia 100 I scan, there should at least be grains it should be able to focus on, and of course dirt, in any area, both dark and bright. Velvia, though, is a real bitch to scan!

If a digital camera was this bad at focusing, it would not be possible to sell it!

I have not found any method other than trying to rescan several times before I get something decent. It appears that success rate increases if I frequently restart SilverFast. I now check every scan batch in 1:1 in Lightroom before I proceed with the next; needless to say, pretty tedious.

Wouldn't it be possible for you to make SilverFast try to focus on several points at once?

[LSI_Muenier]

Dear Harald,

SilverFast is doing the best it can with the scanners it has been ported to.
Some scanners allow a more comfortable way of auto focus, others limit the interface to auto focus. In your case, unfortunately, SilverFast can only tell the scanner "yes" or "no" with respect to auto focus without additional parameters, which other scanner might offer.

Best regards
Martin