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benduross
11-18-2007, 09:42 AM
Hello.

Another one from me...I am a busy beaver at the moment. I am also making a 4x5 camera with a big magnifying glass lens. The focal lengh of the lens is 100mm...so if I set it 100mm away from the film then am I correct in thinking that it's at it hyperfocal distance?

Thanks everyone.
I am teaching English in Korea at the moment and between working here and living in a foreign country and stuff I am trying to build some camera equipment.
In the next month or so I should be able to develp ortho film in my bathroom in trays but at the moment eperimentalion is slow and frustrating so any help would be appreciated.

I have found instructions to make bellows so I think that's probably the next step...

Thanks

Ben

JoeVanCleave
11-18-2007, 01:16 PM
Ben;

This sounds like a fun project. For the lens, if it is rated as a 100mm focal length, that means that subjects far away - near 'infinity focus' - should be sharply focussed at a point 100mm from the rear nodal point of the lens. Since you don't know exactly where this point is at, it's usually best to setup the lens in a test stand (makeshift is okay) and simply measure with a scale the distance from a reference mark on the side of the lens to the sharply focussed image plane.

If you're planning a variable focal length camera (you indicated a bellows), then make the shortest focal length a bit shorter than 100mm (to accomidate errors in measurement and construction), and the longest focal length of the bellows would be determined by how close up you wanted to be able to focus. As you may know, with these LF lenses, infinity focus is the shortest extension of the bellows; as you focus closer in, the bellows has to be extended outward, toward the subject. You can get an idea of how long you want the bellows by simple measurements of the lens image against a white screen with objects at various distances from the lens.

An alternative to using a bellows as a method of achieving variable focus is a nested box camera. Think of a flat, wooden platform with the front half of the camera permanently affixed; the rear portion of the camera nests within the front half, and slides back and forth in grooves cut into the platform. A felt light trap is on the interfacing surfaces of the two box halves. The film holder attaches to the rear of the sliding box, with the lens on the immovable front half.

For an inexpensive and easy alternative to ortho sheet film, try starting out with paper negatives (i.e. black and white photo paper), preferrably graded paper, although multi-contrast will work, it's harder to control contrast. You can either scan the resulting paper negatives, or contact print them in a simple darkroom arrangement, using a dim light source and thick sheet of glass, onto another sheet of paper. I usually use graded RC paper for the negative, and contact print onto fiber paper for the final print.

This project maybe easier than you think; I've built a nested box camera using black foamcore and a binocular lens from a 7x50; it will cover a 5x7 format easily. You can also make a homebuilt viewscreen, just a wooden frame the same size as the film holder, with a plastic screen placed at the same location as the film would be, and sanded down on one side to be translucent.

~Joe