Question About a Build

[wrieselbach]

Hi All,

Tried searching, but as I can't remember the actual term for what I'm looking for, it's kind of fruitless. I need to work out the minimum interior cone for a camera build. In other words, from the lens to the film plane, how do I determine the minimum space needed inside the camera to get the light to the film? I once knew the guidelines for this but can no longer remember, and the notes I have on that are many decades buried somewhere in the house. I want to do this for two possible designs... One a 6x17 and one 4x5. Trying to make the designs as compact as possible.

Thank you!

[Jeff Keller]

Think about the lenses you are going to use.

If you use a lens with an "infinite" focal length you need a bellows at least 4x5 infinitely long.

About the shortest lens which will cover 4x5 is about a 47mm Super Angulon XL. Flange to focal plane 59mm.

[wrieselbach]

Looking at (because I have) 75mm Super Angulon f8, 90mm SA, Nikon 135 f5.6, and possibly as high as a 150 something or other. I know the FFL measurement for each, and the image circle, that's not what I'm looking for.

[Tim Meisburger]

Its a line from the edge of the lens to the edge of the ground glass, if I understand your question. Angle of the line will change with focal length. Focal length changes with distance to subject. Line of sight.

[Jeff Keller]

You need to get the bellows over the rear of the lens. Light travels in a straight line from the glass to the film, so if it clears the rear element and the film at the other end you are fine. A really long focal length lens would require the bellows to be so elongated it would look almost like a box. A short focal length would allow the bellows to be more like a pyramid but unless you shoot really low f no. lenses, the wide angle lenses are likely to have the largest real element diameter. (as Tim says a straight line from the rear lens element to the edge of the film).