Re: Slit width - Distance to fim plane

[David Dobbs <dadobbs@xxxxxxxxxxxxx>]

Hello, I have designed a 180 degree camera design with the drum 2x the focal
length. The 2x drum yields a image 2*pi*FL at 360 degrees. I plan to place the
adjustable slit about 7.5mm from the film drum plane. To solve the banding problem
the camera will have a wind up spring. Several question have presented themselves
in the design process. Where is the nodal point? How does one calculate the true
focal length?
David A. Dobbs
http://www.david-dobbs.com

Alan & Shari Kafton wrote:

> Robert Durn wrote:
> >
> > Hello to all,
> > Does any one have any thoughts or answers to how wide a slit should be and
> > how far it should be from the film plane? I have been building a camera with
> > a 24mm Nikon lens using 120 film stock and a 1mm slit placed 10mm from the
> > film plane.
> > I still can't get a really sharp image even at f16. The film transports
> > around a drum omega style and has an image of 149.5mm for 360 degrees.
> > Also, I know that the rule says 2 x focal length x Pi or 150.796mm but is
> > 149.5mm close enough?
> >
> > Can any one help?
> > Many thanks, Rob Durn Stockport UK
> >
> > also at Robert.Durn@xxxxxxxxxxxxxxxxxxxx
>
> Dear Rob,
>
> One other thing you may want to consider is that often the published
> focal length in not correct -- for wide angle lenses, the actual FL
> tends to be a bit longer.  So if your lens is really 24.5 mm, the
> calculated drum diameter should be almost 154 mm which is now quite a
> bit off of what you actually have.
>
> It turns out that the Roundshot Super 35 or 220VR users manual lists
> actual focal lenghts for some Nikon lenses that must be programmed into
> the camera computer.  If you respond with more details on what lens you
> actually have (i.e. f2.0, f2.8 etc, AI, etc) perhaps one of our list
> readers will look to see if the manual has your lens listed.
>
> While I've never built a camera, I think you'll find the slit-to-film
> distance for most panoramic cameras is closer than 10 mm.  1 mm slit is
> a bit on the narrow side compared to most -- the narrower the slit, the
> more banding-prone your camera will be.  On the other hand, the narrower
> your slit, the LESS prone your camera will be to apparent
> synchronization (out of focus) problems due to your drum being the wrong
> diameter!!
>
> Ah....to be able to afford that great Roundshot Super 35 or 220VR!!!
>
> Best of luck,
>
> --Alan Kafton