JonesLongShot wrote:
Tons o Glass 0 Class wrote:
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.
I still have the teleprompter glass for some reason. It is mirrored on one side and that is the side to aim towards the photographing camera. There is no issue with ghosting in my experiments. Probably because of the single mirrored side.
Hmm. I'd expect a slight "echo" of things from the thickness of the mirror glass. There are plenty of very thin cheap films, often sold for window privacy/UV blocking, that are one-way mirrors. However, a teleprompter is designed to be photographed through, so that's a very appropriate thing to try.
Oddly the projected image just seems to be absorbed by the black walls. I guess you could try reversing the mirror and put the focusing substrate on the wall facing the mirrorless camera. I just didn't try that. I just painted the entire interior black. Vanta Black would probably be perfect.
Vanta Black isn't a paint. Get some Black 2.0 or Black 3.0.
I like the idea of the shift lens too. Just another way to solve the off axis problem. Probably a better solution than mine to be honest as my implementation does have light losses. However it is really easy to get an excellent on axis image and in a fairly compact assembly with a beam splitter.
The shift lens is an elegant solution... although arguably you can do the same just by pointing the camera straight at the image with an offset -- in other words, implementing the shift on the big lens rather than the little one. Of course, using the big one for the shift, you might have the off-axis artifacts of the big lens obviously decentered.
I looked at lab grade beam splitters and quickly decided they were not a good option. The prices prohibitive. Teleprompter glass is easy to get. I purchased samples that were 9 inches by 9 inches for like $12 each. I figured this was effectively a somewhat lofi type of project so lab grade beam splitters probably wouldn't make a huge difference.
High-end teleprompter glass should be very good. I haven't seen any as cheap as $12; I'm seeing more like $60.
The most important material is the focusing substrate as it defines the look and detail of the final image more than anything. I tried lots of different papers and things like white polystyrene and bead blasted aluminum. In the end I liked really fine paper the best. This part still needs lots of experimentation. The finer the surface structure, and the more reflective the material, the more it approaches an actual mirror and that completely destroys the whole thing.
Ordinary white paper was what I ended-up using in the FourSee TDCI Multi-Camera . The best image quality was actually using an Illford inkjet paper, except it was glossy enough to give some reflections.
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
I think his project is fantastic.
Not bad, but pretty pricey with that shift lens...
