Re: filmscanners: Link to Nikon 8000 banding example...

[Stephen Kogge <stevek@uimage.com>]

> > Just a thought. Do you get stop/start motion of the film carrier
> > because of
> > spooling, during the actual scanning process?
> 
> I understand your point, but...the scanner stops for every line anyway, it
> has to...it's just a matter of how long it stops, so providing there isn't
> some some race condition that this long stopping exacerbates, the stopping
> "should", mechanically, not make any difference.
> 
> 

        But does the head actually stop or like a lot of flatbeds scan
"on the fly" with CCD's you can define how long to sample - think of it
as an electronic interrupter shutter - motion artifacts will not be seen
if the relative motion is low wrt the time the CCD is sampling 
this could be as long as a ?? millisecond ???

        There are usually no mechanical shutters with video and still
CCD cameras and they work with motion :-)

        Anyone who has ever used a lathe knows you really want to do
the work in one pass - if/when you stop the backlash in the gears may not
register back to where you left off.

        There is nothing to say you need to wait for the stepper to
stop just that it "ought" to have moved to the next spot. Disks now
use linear actuators and optical encoders, stepper motors have a long
settle time and the gears a backlash. This "banding" could be the
visible backlash as the CCD head gets back up to speed and is at the
wrong place after a pause to dump the buffer or the remote system
to flush its buffers.
 
-- 
        Stephen N. Kogge
        stevek@uimage.com
        http://www.uimage.com