slit width experiments, more questions than answers

[Ron Klein <panorama@xxxxxxx>]

>      Why would reducing the slit size cause banding?  Less light =  slower
> rotation = less of a problem with banding?   Is this being used at auto
> exposure or manual?

Here is where I hope our dear friend Andy Davidhazy steps in... He explained
this problem quite nicely to me at one of the very first IAPP meetings.

I will add, that you might be thinking that a cirkut camera is more
complicated that it is in reality.  There is only a manual type of exposure
system, and the motor doesn't speed up or slow down during exposure to
compensate for light conditions.

 When the motor runs irregularly, you get banding.  When the slit is narrow,
the banding is more noticable as fine lines.  Wider slits tend to blur the
banding somewhat.  I think there is an optimum distance that the slit itself
should be spaced away from the film.  This would give a softer edge to the
slit and reduce banding as well.  The drawback is that you now have an
exposure that is not an exact speed, a minor problem in cirkut work, but in
more modern cameras it could cause soft images when shooting moving objects
at a fast speed.


>       With the 220 VR banding is more common at very high speeds, 1/250
th,
> or when using auto exposure...the drastic slowing and speeding of the
motor
> can cause this......

The auto exposure has me puzzled.  My logic says it shouldn't work very
good.  Imagine a pan shot of a row of dark houses on a clear blue sky.  As
the camera pans, it would speed up and slow down to "correctly" expose for
the dark houses, yet this would screw up the even blue sky that you would
only get by a constant speed.  As well, in fast shots certain laws of
physics must come into play and give banding problems.  With my cirkut work,
slow has always been better except when using original spring motors at the
slowest speed.  Then the power of the spring is dampened by the governor so
much that there is very little power to run the camera smoothly.  Going too
fast causes vibrations and spooling problems as the film is moving from the
spool to the drum.  Since there is a small gap between the spool and the
slit where the film is unsupported, it is possible that it could flutter at
certain speeds, more so when moving fast.

Just remember, banding is caused only in pan cameras!  Point this out with
pride to your customers.  "Hey, look, genuine banding".....a mark of
distinction.

Ron Klein,
in rainy Juneau Alaska with fresh snow on the mountain tops.  Winter is
coming early this year.