flatbed scanner focus questions

  • Thread starter Thread starter J. L. Jones
  • Start date Start date
J

J. L. Jones

I have an Epson 4990 and I understand that it and similar
priced scanners have a fixed focus optical system. Does
anyone know how this fixed focus system can accomodate both
scanning transparancies or flatwork directly on the glass
and scanning film held in the carrier significantly above
the glass?

Do more expensive Epson scanners have adjustable focus? If
so, is the focus set manually or automatically? Does it
adjust as it scans?

What about other scanners? What models have adjustable
focus, and how well do they work?

This seems like a lot of questions, but perhaps others are
interested as well.

Thanks.

Larry Jones
 
Mike said:
Depth-of-field of focus is sufficiently large enough.
Click to expand...

Yes, but still. I have the 4870. For critical work on negatives, you may
want to experiment to find the "sweet spot" of your scanner. It probably
will be somewhere in the middle of the ground glass, and you can make
tests to find the sharpest height (ususally around 0.3 to 0.5 mm above
the glass). Which means that reflection scans would always be slightly
out of focus, unless the epson scanner changes focus when you switch
from reflection to transparency? I don't believe they are that refined...

Louis
 
Louis said:
Yes, but still. I have the 4870. For critical work on negatives, you may
want to experiment to find the "sweet spot" of your scanner. It probably
will be somewhere in the middle of the ground glass, and you can make
tests to find the sharpest height (ususally around 0.3 to 0.5 mm above
the glass). Which means that reflection scans would always be slightly
out of focus, unless the epson scanner changes focus when you switch
from reflection to transparency? I don't believe they are that refined...
Click to expand...

Perhaps you should adjust your beliefs ;-)

Really, I don't have that scanner (I've got an Epson RX500), but the
SANE driver for Epson scanners does include an option to do just that:
--focus position "Focus on glass"
--focus position "Focus 2.5mm above glass"

The option is inactive with my scanner ("inactive" can either mean that
it cannot be used with the other current settings, or that it is not
available on the scanner - in my case it's the latter).

But if it is there it must be because other Epson scanners can react to it.

In the source there are the following comments relating to focus:
"Added support for the "set focus position" command, this is
necessary for the Expression1600."

"Check first if the scanner does support the set film type and
set focus position before the GUI elements are displayed."


Also, this command seems to only be implemented in "Level F8" scanners
("levels" are the various versions of the Epson scanner communication
protocol; the digit indicates backwards compatibility with scanners that
use a protocol with the same letter but a smaller digit; more can be
learn at http://www.epsondevelopers.com ).


by LjL
(e-mail address removed)
 
Lorenzo said:
Perhaps you should adjust your beliefs ;-)

Really, I don't have that scanner (I've got an Epson RX500), but the
SANE driver for Epson scanners does include an option to do just that:
--focus position "Focus on glass"
--focus position "Focus 2.5mm above glass"

The option is inactive with my scanner ("inactive" can either mean that
it cannot be used with the other current settings, or that it is not
available on the scanner - in my case it's the latter).

But if it is there it must be because other Epson scanners can react to it.
...
Click to expand...


Great info, Lorenzo, thanks! I have to find out if the 4870 is in that
group or not (F8 etc). Interesting links also, ImaTest and EpsonDevelopers.

Louis
 
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