5x7 on 35mm digital

[Noeyedear]

I thought I had already posted this, I can't find it so a mental relapse on my part.
I have a 305mm portrait lens fitted to my 5x7 camera, can anyone think of a technique to capture the 5x7 field of view on an attached 35mm digital. I'm sure this would be possible, I only can think of reasons why it can't be done. It would be a great way of testing the shot etc Any ideas as to which lenses, condensers or magic words need to be used?
Shooting the GGS is not an option.

Kevin.

[venchka]

I know just enough to get in trouble...

5x7 and full frame 35mm won't have the same aspect ratio.
You might be able to set up your 305mm lens/5x7 camera and a full frame 35mm camera with a zoom lens. By fiddling and twiddling you may be able to almost get the same coverage with both setups. I'm guessing. Big time guessing. Somewhere around 70mm to 90mm the small FOV will approximate the 5x7 field of view.

I know that those who know will correct me soon enough.

Good luck.

[Noeyedear]

I know just enough to get in trouble...

5x7 and full frame 35mm won't have the same aspect ratio.
You might be able to set up your 305mm lens/5x7 camera and a full frame 35mm camera with a zoom lens. By fiddling and twiddling you may be able to almost get the same coverage with both setups. I'm guessing. Big time guessing. Somewhere around 70mm to 90mm the small FOV will approximate the 5x7 field of view.

I know that those who know will correct me soon enough.

Good luck.

Yeah I could do that, I wanted to shoot with the lens, movements and position of the LF camera. I know the answer is not simple, it's sort of gearing down the image. It must be possible......... isn't it?

Kevin.

[Maris Rusis]

It can be done in two difficult but possible ways.

Number one problem is to redirect the light rays that the 305 portrait lens sends out to form the real 5x7 image. This image is ordinarily destined to fall on a 5x7 piece of film but if the rays are caught and turned after they have passed the focal plane they can be re-focussed on a digital sensor. Just taking pictures of the ground glass is an easy and cheap way to do that but, if that's out, a highly corrected condenser lens with an entrance pupil bigger than the 5x7 frame and a converging power greater than the 305mm portrait lens (more than 3.0 dioptre, for example) could theoretically do the job. Such a condenser lens, if it existed, would be a colossal optical marvel.

Another way is to fix the small camera to a contrived two hole lens board (one for the 305 lens, one for the small camera lens) for the 5x7 camera so that the 35mm looks down into the bellows and at the focal plane. Placing a white surface in the 5x7 focal plane should yield a lookable and photographable reflection image. All this amounts to some fancy optical engineering but it's possible if the 5x7 lens board is big enough.

[Nathan Potter]

Maris, I think what you are suggesting with your first approach is to re-capture the full 5X7 aerial image of the 305 mm primary lens at the point where the GG is usually located and then refocus it at some further distance on the 35 mm digital sensor - if I have this right. I then assume this would be a closeup lens that would focus at several inches distant with a subject field of view of 5X7 and an image plane of the size of the sensor. However the off axis rays from the 305 would require a custom, unprecedented degree of correction to yield the equivalent flat field of the subject - as you point out. Such an approach does not seem feasible without designing a special lens.

Your second approach is the best, and using a bit of swing enough distortion can be produced on the white board to just compensate for the off axis view from the digital camera.

Nate Potter, Austin TX.

[Noeyedear]

It's not looking very feasible, I'm wondering if photographing some material other than glass in the GGS position would be possible like a thin white perspex? I don't think I will dedicate any more brain power to this musing, I have limited resources in that department.

Kevin.