Canon FS4000US focus

#11

On 14 May 2007 09:14:14 -0700, DenverDad <the_applegates (AT) comcast (DOT) net>
wrote:

Quote:

Brian,
You may be aware of this
already, but there is a small "+" symbol which appears in the preview
scan. This is the location in the frame where the focusing routine
measures to find best focus. Since there is always at least a little
bowing of the film in its holder, it is important to set the mark to
an appropriate location. Make sure that it is NOT placed near the
edge of the frame (or worse yet, out of the frame). Rather than
placing this mark right in the center of the frame, I find that it is
usually best to place it somewhat away from the center - say half way
between the center and an edge. This makes best use of the depth of
field of the scanner optics and usually insures that the entire frame
will be in sharp focus. You should be careful that this mark falls on
an area which has high contrast and is not too dark.

Jeff & Roger,

Thanks for reminding me of the focus indicator. I had been neglecting
to observe its position on each scan. I tried all of the suggestions
concerning manipulating Vuescan and I found that the best results, for
me, come from making a multi-pass scan.

Since I'm in the habit of scanning complete rolls I don't normally
bother with multi-passes. I will do that in the future on individual
frames that are to be displayed or printed.

Thanks to you two plus Colin D. and Steven Saunderson for the input.
All of the information was helpful in analyzing my work habits and my
equipment.

Brian

#12

On Thu, 17 May 2007 16:16:23 -0400, Brian Wickham
<bwickham@NO~SPAM.nyc.rr.com> wrote:

Quote:

I believe the auto-focus operation uses only one vertical line in the
scan. The horizontal position (scan line #) is determined by the
carriage position and the vertical top and bottom are specified in the
command parameters.

If I read you right an improperly aligned strip in the carriage could
have a deleterious effect on the focusing function. Is that correct?

Yes it could but I haven't expressed myself very clearly here. The
carriage holds the film holder and is positioned by the fine stepper
motor. The carriage contains a coarse stepper motor which moves the
film holder. All this movement is along the X-axis. Focussing is done
by moving the lens along the Z-axis. It would be difficult to misalign
a film strip in the holder but I have had trouble with curled film that
doesn't sit flat in the holder.

The PC software will focus the scanner using two commands. The first
will move the film holder (using the coarse stepper motor) to select the
position on the X-axis. Then the focus command is done and the FS4000US
moves the lens (on the Z-axis) and finds the sharpest scan of the
vertical line. Two parameters in the focus command specify the limits
(on the Y-axis) of the scanned line.

Vuescan allows you to select the focus point but after I viewed a log it
looks like only the scan line number is used. Vuescan calls this the
Y-point because the scan lines in the display are horizontal rather than
vertical as they are in reality. The other setting (X-point) appears to
be ignored and the area starts at pixel 500 and stops at pixel 3500.

I think Roger's offer of commenting on one of your scans is excellent.
If you like I can upload a test scan so you can view it for comparison.
If you need a temporary location for uploading one of your scans please
ask and I will arrange something.

--
Steven

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Canon FS4000US focus

Scanners And Imaging Devices Scanners Discussions (comp.periphs.scanners)

Re: Canon FS4000US focus - 05-17-2007 , 03:30 PM

Re: Canon FS4000US focus - 05-17-2007 , 06:45 PM