Box camera help needed

[iangreenhalgh1]

Hi folks

I've turned a cardboard box into a rudimentary 8x10 camera to try out a legendary 8x10 lens before I give it back to a friend.

It's 312mm focal length, so what I need to know is this - do i place the film plane 312mm from the back of the lens or 312mm from the iris/vertex of the lens? Assuming infinity focus of course.

[Xpres]

The distance from the back of the lens to the film plane is the back focal distance which is not the same. The focal distance is from something called the rear nodal point to the film plane and its position depends on the type of lens. If there is an aperture, or slot for stops, that might be a good place to start.
You could use a box within a box and some tracing paper to visually work it out as you build your camera?

[iangreenhalgh1]

I guess I'll have to use a sheet of white paper and see where I get a focussed image, like a camera obscura.

[philslizzy]

I thought you would have know that Ian! You will when you've tried this! Good luck.

oh any caffenol recipes for paper?

[David]

Stop it down to f165 and call it a day.

[iangreenhalgh1]

I've got x-ray film and dk-50 to use, or paper and d163 as a backup.

It only stops down to f64 and it's stuck at f22, the aperture needs servicing.

[kansalliskala]

[monkjason]