Re: slit width experiments, more questions than answers

[Michel Dusariez <dusariez@xxxxxxxxx>]

OO

>>      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.


Michel DUSARIEZ
UNLIMITED FIELDS RESEARCH PANOPTIC IMAGING
KITE AERIAL PHOTOGRAPHY WORDWIDE ASSOCIATION - FOUNDATION
14, Avenue Capitaine PIRET
B-1150 BRUXELLES - BELGIUM
Fax 32 2 512 68 29