Adapting projector lenses.
Jul 5, 2020 17:28:20 GMT
on Jul 5, 2020 17:28:20 GMT
Last Edit: Jul 5, 2020 18:54:47 GMT by lumiworx
After an impulse auction bid got me a 1950's Leitz Prado 500 projector with a spotless lens, I thought I'd pass on a few bits and pieces on my experience in case anyone else might be tempted to do the same. I don't know any technical details on movie or slide projection systems, so anything I can offer is anecdotal and purely experimental, and just relates to the Hektor lens that came in the box.
The Prado projectors from the 1930's to the 50's-60's all seem to use an interchangable lens assembly, where the lens and it's tube will unscrew from the front of it. I've read that some of the earlier types had LTM 39mm threading, but the Prado 66/250/500 models uses a larger diameter of 54-ish millimeters. I looked for something ready made from RAF and a few others, but nothing to be had that was close enough. A few years ago I bought a dirt cheap ($11) EOS to Sony E-Mount 'dumb' adapter to test a Canon lens. Unfortunately the adapter wouldn't help since it couldn't set apertures mechanically. Useless for me to use on EOS lenses, but it did have a large enough throat once the mount ring was removed. Without that piece it swallowed the end of the Leitz focus tube and squared it to the base with almost no slop at all.
It was good enough to confirm that I might be able to keep the threaded focus tube and lens intact as a focusable unit. After some packing tape to keep everything in place, I found that it was usable and focusable without any light leaks. It is absolutely razor sharp and had great contrast and color with very reasonable CA, but it did exibit a habit of throwing a rather intense glow around any highlights and whites in the frame. I think most of us have seen similar issues with a lot of ML f/1.9 or f/2 lenses that need to be stopped down one notch to clear up the image, but probably not as extreme as the Hektor and not as blue in color as it throws off. You can see it in the shot of the Yashica-A around the sportfinder's raw metal edge ring that I posted in the "Toys" topic.
I took a small patch of 0.5mm neoprene sheeting that was easy to cut and made a Waterhouse stop out of it. It looks like a black rubber washer with only about a 3mm width of material to make the 'iris'. I pushed it into the rear of the lens and up to the back element in the rear group. I didn't want to cut down the speed much - just enough to get rid of the glow. That was enough to do the trick, but it needs to be cut better to keep the bubble bokeh less fuzzy, so I'll need to find something stiffer and thinner to use more permanently.
One more confirmation after more testing... I don't need to make any modification to this setup to get infinity focus. The only 'gotcha' now, is that the lens will unscrew completely out of the tube when focusing in to reach close range subjects. Close focusing is now at about 5 feet or so. not really close, but not bad either.
A few more test shots after inserting the stop.
A trio of ST-7 tripods...
A Cell tower (almost in my back yard) with a massive amount of antennas...
More photos and larger sizes of these are in the testbed gallery.
The Prado projectors from the 1930's to the 50's-60's all seem to use an interchangable lens assembly, where the lens and it's tube will unscrew from the front of it. I've read that some of the earlier types had LTM 39mm threading, but the Prado 66/250/500 models uses a larger diameter of 54-ish millimeters. I looked for something ready made from RAF and a few others, but nothing to be had that was close enough. A few years ago I bought a dirt cheap ($11) EOS to Sony E-Mount 'dumb' adapter to test a Canon lens. Unfortunately the adapter wouldn't help since it couldn't set apertures mechanically. Useless for me to use on EOS lenses, but it did have a large enough throat once the mount ring was removed. Without that piece it swallowed the end of the Leitz focus tube and squared it to the base with almost no slop at all.
It was good enough to confirm that I might be able to keep the threaded focus tube and lens intact as a focusable unit. After some packing tape to keep everything in place, I found that it was usable and focusable without any light leaks. It is absolutely razor sharp and had great contrast and color with very reasonable CA, but it did exibit a habit of throwing a rather intense glow around any highlights and whites in the frame. I think most of us have seen similar issues with a lot of ML f/1.9 or f/2 lenses that need to be stopped down one notch to clear up the image, but probably not as extreme as the Hektor and not as blue in color as it throws off. You can see it in the shot of the Yashica-A around the sportfinder's raw metal edge ring that I posted in the "Toys" topic.
I took a small patch of 0.5mm neoprene sheeting that was easy to cut and made a Waterhouse stop out of it. It looks like a black rubber washer with only about a 3mm width of material to make the 'iris'. I pushed it into the rear of the lens and up to the back element in the rear group. I didn't want to cut down the speed much - just enough to get rid of the glow. That was enough to do the trick, but it needs to be cut better to keep the bubble bokeh less fuzzy, so I'll need to find something stiffer and thinner to use more permanently.
One more confirmation after more testing... I don't need to make any modification to this setup to get infinity focus. The only 'gotcha' now, is that the lens will unscrew completely out of the tube when focusing in to reach close range subjects. Close focusing is now at about 5 feet or so. not really close, but not bad either.
A few more test shots after inserting the stop.
A trio of ST-7 tripods...
A Cell tower (almost in my back yard) with a massive amount of antennas...
More photos and larger sizes of these are in the testbed gallery.