Autofocus problem with Nikon LS4000 and SF200

[r_moeller]

I have just started to use the ADF frequently. After scanning and revising a number of slides (2000+) I found that sometimes slides are out of focus. This may be one or up to five slides in a batch of 25. Unsharp slides are not sequential. All slides in a batch are the same film typ. The error is not reproducible. If I scan the same batch again it may give no out of focus slide or other slides out of focus.

I wonder whether this is a hardware or software problem.

Many thanks for any help or idea about further testing to solve the problem.

[LSI_Ketelhohn]

Dear Mr. Moeller,

normally the focus is set by the scanner.
Is the focus option set to automatic?
If it is set to manual the focus might be set to a fix value not suitable for all slides.


kind regards
Arn eKetelhohn.

[degrub]

The Nikons have a very narrow depth of field. If the film is not within about +/- 5 Nikon focus units of the focus point parts of the image will be out of focus slightly. Many slides will be this way. Try manual focus on those slides and see if it helps. If not, then the slide is not flat enough and could be remounted. The other issue can be that the software is picking a spot that is not representative of the entire slide. If i remember correctly, Nikon's autofocus algorithm is based on contrast edges. Manual focus can deal with this.

[r_moeller]

Many thanks for the replies.
While doing a batch scan I have always switched 'automatic' autofocus on (marked _A on the autofocus button) so that the focusing point should be the center of the slide. If the reason would be a curved slide I would expect a viewable difference in sharpness with an infocus area in the middle and out of focus at the edge of the frame. But the scans are totally blurry. All slides are mounted with the same typ of mounts. I don't know whether the tolerances of the mounts are big enough to make autofocus impossible on some of them? I think if that's the case I would even have more troubles with manual focus when scanning a batch.
And scanning the slide a second time may result in a correctly focused scan. That can be because of a slightly different alignment of the silde so that the focus point differs a little. Anyways I would not expect such a high number of out of focus scans.

[LSI_Luebker]

Dear Customer,

how is the foucs when you scan with a Single Frame holder like the Nikon MA-20 ?
As it could also be that your SF200 is causing the focus problems. But as degrub pointed out it could also be that the sildes need to be scanned with Manual Focus when they are not plain in the frames.

[r_moeller]

Dear Mr. Luebker

so far I had no problems while scanning single slides with the MA-20 adapter. Shouldn't be at least the area of the focus point focused properly when the slide isn't flat in the frame?

[degrub]

i very seldom see the focus point in the center with the Nikon. It is usually on a high contrast edge in the image.

[r_moeller]

So 'automatic' autofocus don't mean that the focus point is in the middle of the image? That was always my idea because of the focus point shown by Silverfast.

[LSI_Heidorn]

Dear r_moeller,
actually your assumption is right, auto-focus MEANS to focus in the center of the image.
I assume that degrub is saying: "as a suitable focus point is very rarely in the center i normally set the focus point manually to a high contrast area in the slide".

@degrub: did i get you right ??

best regards,

Nils Heidorn

[r_moeller]

Dear Mr. Heidorn

thanks for the reply.
I still believe that the scanner wasn't able to acquire focus at all for that slides.
Is there any reply from the scanner to the controlling software that autofocus failed? If that's the case, is this information written to a log file for batch scanning?
Batch scanning with the SF200 would have little pros when there is the need to scan only with manual focus.

Best regards
R. Moeller

[LSI_Heidorn]

Dear Mr. Moeller,
in most of all cases the Nikon *finds* a good focus when starting in the middle. The Area is not a small pinpoint but an area around the center, so it works most of the time.
Sadly there is no "focus failed" message, the scanner simply chooses a wrong focus...

best regards,

Nils Heidorn

[r_moeller]

Dear Mr. Heidorn

in most of all cases the Nikon *finds* a good focus when starting in the middle.

That is really different from my recent experiences where I have scanned 25 slides and 6 were out of focus. I am still wondering whether this is because of a hardware problem. But it seems that it is not possible to find out from a scanner response to the software?

Best regards
R. Moeller

[LSI_Heidorn]

Dear Mr. Moeller,
the scanner never fails focussing so you can not know wether the last focus was a "good" one or a "bad" one...
Obviously a scanner defect could make this problem worse or visible...

best regards,

Nils Heidorn