JonesLongShot wrote:
I hope this information is relevant. Seeing this brought me back to thinking about a project I was experimenting with before I left the US. Now I don't have the resources to play around with it.
Top view of camera
The diagram is a top view of a camera I made to do a proof of concept. Well it was all cardboard and hot glue but did indicate the idea could be workable.
I mounted a 300mm lens in one end of a cardboard box that fit over another cardboard box like a sleeve. Inside the inner box was a beam splitter. A partial mirror used for making teleprompters.
In the side of the entire assembly was a mirrorless camera. The idea was that the image was focused on an opaque white screen at the back of the camera and the partial mirror allowed the digital camera to focus on the projected image..
I had remembered something about Canon's pellicle mirror camera from the 70s or so and thought that this kind of setup could allow for using long lenses in a variation of the "photographing the focusing screen" type of projects. When I had played around with photographing the focusing screen of my 4x5 view camera I had all the issues of light fall off. With this arrangement that was greatly reduced. And it made for a nice compact setup. There were lots of mechanical issues to be resolved but my experiments were very promising.
I was doing all of this while selling our house and moving to another country so I have lost all my notes and photographs I'm sorry to say.
Jones
Cool concept, I like it. Teleprompters look cheap enough so that would be fun to try. There must be lots of light bouncing around. If you had another opaque focus screen on the top, would your camera see a nearly full-brightness image that is the result of the two superimposed on one another? What about ghosting? I suppose that could be an issue so maybe the rest of the box would just need to be as black/light-absorbent as possible instead.
One more variation of these photographing-the-focusing-screen type rigs is by using a tilt-shift lens to image the projection, like Zev Hoover did for his "large format video camera":
https://www.dpreview.com/articles/3423280809/how-i-built-a-large-format-8x10-video-camera