minimum focal length for a sliding box camera?

[Schunn99]

Hey Apug,

I am looking to build a 4x5 sliding box camera, I am going to build a 4x5 landscape lens like the one described in Primitive Photography. The focal length of the singlet lens is 200mm. Does anyone know is a good minimum focus length should the box be when closed? For example in the book, for the 8x10 sliding camera, Alan Greene describes the camera's focus as a minimum of 8 inches closed and 16 inches fully extended. Should I just half the dimensions to 4 inches and 8 inches for 4x5?

thanks,
Scott Hunnicutt

 

[FM2N]

The focal length for a 200mm lens would be 200mm at infinity or 7.87 inches so to be safe a minimum of 7.5 inches and a max of 15.00 I don't think it matters if the film is 8x10 or 4x5
I hope this helps-
http://www.f295.org/Pinholeforum/forum/Blah.pl?m-1270042193/s-0/highlight-sliding+box+camera/#num0
Arthur

 

[Ian C]

A single element lens of 200mm focal length requires the center of the lens to be 200mm from the film plane at infinity focus.

Decide what minimum close focusing distance (film to subject) you require. Then you can calculate the greatest lens to film distance that’s needed.

If you want the ability to focus to 1:1 (image size/object size), then the center of the lens must be 400mm from the film and the lens center will also be 400mm from the object.

If you don’t need that much close focusing ability, then the lens doesn’t need to extend as far from the film plane.

For example, if your camera only allows extending the 200mm lens 300mm from the film, then the closest film-to-subject distance is 900mm (still fairly close) and the magnification is 1:2.