Replacement beam splitter glass

StepheKoontz

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Today I ran across something I have never seen before. I was cleaning the viewfinder in an old minolta "A" rangefinder and the angled beam splitter/semi silvered glass was real hazy. When I went to clean the side that is towards your eye, the gold colored reflective coating turns out is super soft and just wiped off the glass. I just barely touched it with a wet q-tip and it came off. Of course this destroyed the rangefinder patch being visible It was so hazy as be be mostly unusable anyway but now it's a scale focus camera.

I've cleaned out dozens of viewfinders before and never seen anything like this. My question is, does anyone have any idea where to source normal hard coated beam splitter glass I could replace this one with? Or is there a film that can be applied to it? It's just a flat piece of glass that has the half silvered coating on it. TIA
 

shutterfinger

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This is quite common on Kalart Rangefinders and Graphic rangefinders. I do not know if it was the coating used or exposure to UV (sun) light that causes the failure. I've had light touch dry wiping to remove the coating.
Ebay search for beamsplitter turns up what you need however you will have to cut a piece to size and shim it as the new stuff is thinner than the old. The current is clear silvering, no amber tint. The coated (silvered) side faces to the user and is shimmed so that the silvered side is in the same position as the original.
Rangefinders use 50/50 beamsplitter.
 

shutterfinger

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There was a time that Edmund Optics had no beamsplitters but they do now.
Sorry I missed the thickness. Pre cut, prefect fit.

I recently replaced the beamsplitter, also called transparent mirror, in a Kalart rangefinder and by placing the reflective side, sometimes difficult to determine, at the exact position the the failed mirror was in I only had to retouch the infinity setting for the new rail position for infinity on the Speed Graphic. The mirror in the Kalart was held at the base and I used strips of a piece of scrap sheet film for the shim stock.
 
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StepheKoontz

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This camera the reflective side is against the machined mount pads with some spring clips holding it against them. This new glass is 1mm but if I put the reflective side in the same plane the old one was, the thickness shouldn't affect anything, the spring clips can easily deal with this difference in thickness. Not that this is some high end camera, I just hate having any camera in my collection that doesn't work reasonably well. In addition to the viewfinder being extra hazy, it shares the issue the camera in the article has with the speeds below 1/25 being sticky. I think I'll just fix the viewfinder and leave the oddbacck backwards installed shutter alone lol.

https://www.mikeeckman.com/2017/09/minolta-a-1955/

Here is a link to getting to the shutter to clean it. I honestly think I can just live with 1/25 being the lowest speed for this much work

http://pheugo.com/cameras/index.php?page=minoltaa
 
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shutterfinger

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Should work if the spring clips don't break. The ones I'm familiar with are brass and break easily.
That Prontor shutter isn't too dificult to service once you remove all the junk from the front. You can likely leave the shutter case with aperture blades and rear lens cell in the camera and remove the rest, clean, lube and reassemble.
https://drive.google.com/drive/folders/0B1sPJkp-MdghNGM1aGY5akgtTmc?usp=sharing
 
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StepheKoontz

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These clips should be fine, they are more like a spring loaded shoe on each side the glass slides between them and the machined face.

Unfortunately this camera has the shutter in backwards. The "front" face you remove to clean and lube it faces the film lol. I've cleaned a bunch of these types shutters before but this camera you have to almost completely disassemble it to get to the "front" of the shutter.

http://pheugo.com/cameras/index.php?page=minoltaa

One day I might get adventurous and try.
 

mshchem

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I got so frustrated with a old Crown Graphic, that at least 25 years back I cut down a piece of glass from an old Polaroid Big shot. I epoxied it right on top of the existing mirror still working fine. Not what you would call elegant but it's bright and accurate
 

bernard_L

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Facing same problem, but residing in Europe, this
https://www.ebay.com/itm/Optical-Pl...Wavelengths-3-x-2-50-R-/133486263107#viTabs_0
would set me back about 50$ (shipping!)
I found these:
https://fr.aliexpress.com/item/4000712216475.html (50/50)
https://fr.aliexpress.com/item/4000860612382.html (50/50)
https://fr.aliexpress.com/item/4000860746065.html (dichro)
https://fr.aliexpress.com/item/4000781659749.html (20/80)

I bought one lot of these just to try
https://www.surplusshed.com/pages/item/L14550.html
but keep in mind that not only the RF patch but the whole FOV will be dichroic; do you want to compose seeing the scene through a blue (or yellow) filter?
Anyway, if you would like one, I can send it for the cost of postage
 

ic-racer

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I'd probably try to re-mirror the existing glass with something like Rust-Oleum 267727.
 
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StepheKoontz

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ic-racer said:
I'd probably try to re-mirror the existing glass with something like Rust-Oleum 267727.
Click to expand...

I thought about trying this but how would you "half" mirror it? i.e. you have to look through this piece of glass, it's not just a mirror.
 
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StepheKoontz

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bernard_L

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Please correct me if I'm wrong, but I seem to recall seeing two kinds of RF: in some, the RF field of view is defined by a small patch (possibly dichroic) on the splitter plate (the rest being clear); in others, the RF field of view is defined by the RF window, the splitter plate being uniformly semi-reflective. In case the splitter is color-neutral, one might create a color difference betwen the two images (helpful for detecting coincidence) by inserting colored gels in one or both of the paths; this might be useful to restore the experience of a RF when the dichroic patch has been (unfortunately) wiped away. I have not tried this yet, but can report that a neutral density (0.3D maybe) in the main path allows to balance the brightness of the two images, and the loss of light in the main image is a tolerable price to pay to obtain the balance between the two images and concomitant comfort of adjustment.
 

shutterfinger

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I have seen two types of rangefinders. One uses a prism to reflect light from the scene onto the beamsplitter while the other type uses a mirror to reflect the light from the scene to the beamsplitter. The window on the front of the rangefinder determines the size and shape of the image seen when looking through the rangefinder. Even when both the prism/mirror and the beamsplitter are the same color its easy to focus in low room light. Addition of a filter of any type only tends to dim the image and does not improve ease of focusing in my test.
 
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StepheKoontz

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I decided to also try order of these.

https://www.ebay.com/itm/Optical-Pl...le-Laser-Wavelengths-3-x-2-50-R-/133486263107

I was able to cut it to the right size with a carbide cutoff wheel I have for my dremel tool. The finder now is REALLY clear but there must be a slight dichromat effect to this splitter as the field is very slightly magenta and the rangefinder patch is very slightly cyan but it REALLY pops now. It's a huge improvement and the sheet is big enough to make beam splitters for a bunch of cameras out of it. Make me wonder if this would be an upgrade for my fuji 645 rangefinder with it's very hard to see patch.
 
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StepheKoontz

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It's glass. And the blade is a diamond blade, I got it for cutting some tile but works great for cutting this super thin glass. #545 I made sure I was cutting on the non-coated side, just go slow and make sure the first light pass goes all the way across the sheet. You can also use the blade to clean up the edges. WEAR SAFETY GLASSES!

Also another tip, you can tell which side is coated by looking through the glass at the edges with a magnifier. It's real obvious which side the reflective coating is on, that side goes towards your eye.
 
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StepheKoontz

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Really excited to discover this repair. I have several old rangefinders that have horribly dim viewfinders caused by it appears to be this same old school beam splitter technology that has deteriorated. Working on an olympus 35 and installed a new one in it. This one was glued in place so used pliobond to reglue it. These are super sensitive to even slight angles, throwing the vertical alignment out and when using contact adhesive like this, it's fairly simple to make these slight adjustments before it sets up. Here I have a screwdriver holding the new beam splitter while it's in the final drying stage. The instructions say it takes 48 hours to fully cure.

 
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