Re: Narrowing the slit on OLD pan cameras

[Alan & Shari Kafton <shmooze@xxxxxxxxx>]

MMagid3005@xxxxxxx wrote:
> 
> Alan -- I understand that if the film is not at the focal length the image
> will be blurred.  But please explain why narrowing the slit reduces the blur.
>  The shutter speed is faster, but the f/stop remains the same, therefore the
> depth of field (if that's the correct term in this situation) should be the
> same.  I'm having trouble getting past this concept, so please help. -- Marty

Hi Marty,

I see Kurt beat me to it & provided a great anwswer.  Another way to
visualize this is to imagine placeing a standard 35mm camera on a tripod
and snap a picture.  Now imagine if you could advance the camera exactly
half a frame & rotate the camera exactly the theoretical angle that half
a frame represents using your selected focal length.  If everything were
perfect, the image in the exact center of the 2nd shot will exactly
overlap the starting edge of the first shot.  Because of the exact
overlapping, no slurring (to use Kurt's words) of the 1st & 2nd shots
will be visible.  If they were not exact, you would see a double
exposure.

This is what happens in a rotational camera, except mis-synchonization
is a cumulative effect that shows up as slurring rather than double
exposure.  The narrower the slit, the less accumulation of this error
can take place.

--Alan