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New Beamsplitter. Egads!

 
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Sjixxxy



Joined: 27 Apr 2004
Posts: 108
Location: Midwest US

PostPosted: Fri May 28, 2004 11:15 pm    Post subject: Reply with quote

My nice new piece of 50mm x 50mm 50% beamsplitter came today so I can replace the useless one in my rangefinder.

I don't own a glass cutter, so I call up the local glass man who lives down the street and tell him I have some special glass that I need a little piece cut out of. "Sure. I can do that quick. Bring it over." I give him the 1mm thin piece and for about the next ten minutes he just mutters "Holy Shit" about once every 15 seconds. This couldn't be good. I give him a piece of paper with the dimensions I need written on it, and tell him the instructions I read say to just score the glass and break it off with in a vise.

Well, since he in the pro he puts in onto his carpeted work table, while I'm thinking that that will be way to soft to score the glass. He tries putting all his weight into one cut and *snap* one corner of the beamsplitter glass goes flying while he keeps mutters "Holy s.. I never seen anything like this before." "This can't be glass. If it was glass I know it would be glass. This is some sort of plexiglass." He grabs his plexiglass cutter and I remind him just to score it and we can snap it. Again he trows a ton of weight into itr and again *Snap" beamsplitter shards all over. I'm thinking "Ugh. Looks like I'm ordering another piece and buying my own glass cutter." One piece was still larger then the size I needed so he grabs it "I don't know what this reflective stuff is made of, but I bet I can grind it to your size." Sure I thought, expecting another failure. Well. After some grinding and swearing he got a piece down to the size I needed, along with a pile of now worthless to me beamsplitter shards.

On to step two, removing the old beamsplitter. I grab it with a pliers and it snaps off like I expected. I figured the part where teh glu meets the metal was going to give hell, and it did. I picked and crush and scraped with every sharp tool I could find for about 30 minutes before noticeing that the blade of a handsaw fits nicely in the groove. Another 15 minutes workign with teh saw and finally the last pice of old glass came lose.

Now I get to attach the new piece of glass into the old slot and just have to ask one thing. Since the 1mm glass is a bit thinner then the original glass, will it matter if I attach it to the top or bottom side of the groove? Will the upcomming calibration take care of that regardless of where it goes?

Also, any tips on kepeing the glass square when I glue it?
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Sjixxxy



Joined: 27 Apr 2004
Posts: 108
Location: Midwest US

PostPosted: Sat May 29, 2004 1:46 am    Post subject: Reply with quote

Bah. roadbumps, and this time they seem large enough to stop me.

The new beamsplitter helped a bit, but while trying to calibrate the finder, I realized it was still really hard to see teh split image without filtering one of the windows. Indoors to to the 20 foot test I couldn't make out anything. Then I realized that the silver backing in the bottom prism was pretty much shot. About half of it is still there which alows a meager amount of the image to be trasmitted, but the rest is just speckled black.

I have a feeling that finding a new prism is out of the question, and that I'd probably have to find a whole new camera with a good prism if I wanted a used part to replace it from. I can think of two posible solutions.

1) Removing the prism and somehow getting it resilverd. Is such a think possible on the hobbiest level? A mirror backing in a can type deal?

2) Removing the prism and just glueing a small square of mirror in its place. Could this work? I don't know much on optics, but it seems al the prism is doing is bending the light around the corner. A flat mirror would do the same thing, is there some signifcant reason why a prism would have been used instead?
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Sjixxxy



Joined: 27 Apr 2004
Posts: 108
Location: Midwest US

PostPosted: Sat May 29, 2004 2:05 am    Post subject: Reply with quote

Scratch that about the prisom. I swore it was in mint shape earlier when I was looking at it, and it seems it is. Thing is that I used a little glass cleaner on it and some of the cleaner made its way under the prisom which turned it black. I thought I was going crazy when I noticed that the black was getting thinner then it was before. I smudged up the prisom while toying with it, so applied a little more cleaner and actually watched it go under and turn it black.

I feel better now.
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t.r.sanford



Joined: 10 Nov 2003
Posts: 812
Location: East Coast (Long Island)

PostPosted: Sat May 29, 2004 2:07 am    Post subject: Reply with quote

I think it would be a good deal easier to find a right-angle prism of the right size than to find a beamsplitter. They are much more common components.

There seems no reason that a first-surface mirror wouldn't work, either, if you were able to mount it so the surface lay in the same plane as the hypotenuse of the former prism.

There are several services that realuminize telescope mirrors and diagonal prisms, and they might be willing to refurbish your prism; it's the same process. If doable, this probably would be worth doing; mirrors nowadays are a lot more reflective and durable than they were half a century ago.

As for mounting the beamsplitter, it seems reasonable to suppose that the coated side is the important one, and you ought to install the thinner piece so that its coated side lies against the same side of the groove as the equivalent surface of its thicker predecessor.
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45PSS



Joined: 28 Sep 2001
Posts: 3160
Location: Mid Peninsula, Ca.

PostPosted: Sat May 29, 2004 3:09 am    Post subject: Reply with quote

Somewhere on this board in the distant past someone posted about repalcing the mirror in a rangefinder, a search might turn it up, and the trick was to put a thin piece of cardboard, book match type, along the back edges of the replacement mirror to take up the thickness distance.
Stick to using Windex or Isopropyl Alochol to clean the optical components of a camera except the lens. Ground glass and fresnels, ektalite screens as graphic likes to call them, can be washed in mild soapy water and rinced with photoflow solution successfully if NO HARD RUBBING or abrasive cloths are used.
And yes, a hand held glass cutter on a solid surface would have resulted in a piece that was useable, not perfect.

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The best camera ever made is the one that YOU enjoy using and produces the image quality that satifies YOU.
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Sjixxxy



Joined: 27 Apr 2004
Posts: 108
Location: Midwest US

PostPosted: Sat May 29, 2004 4:27 am    Post subject: Reply with quote

It was windex that got under the prism and scared me into thinking it was shot. It dried and cleared up now, and all seems well. Just took a peek at my target through the rangefinder that I was using earlier, and this time I was able to see both images. So it seem to be all good.
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Top



Joined: 06 Apr 2002
Posts: 198
Location: Northern New England USA

PostPosted: Wed Jun 02, 2004 1:27 am    Post subject: Reply with quote

I think you might be a guy to avoid in a thunderstorm.
I just did the same job with no troubles. The old beamsplitter slid out of the frame after breaking the old glue bead with a hobby knife, and cutting the new one to fit from the same piece of glass you used took 10 minutes and a 4.99 glass cutter from the hardware store. In fact, I cut five of them. If you need one, PM me with your address and I'll send you one.
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Sjixxxy



Joined: 27 Apr 2004
Posts: 108
Location: Midwest US

PostPosted: Wed Jun 02, 2004 1:54 am    Post subject: Reply with quote

Wish I had read that about two weeks ago. Could have saved me ten bucks. I don't need one though, the chunk that remained of my beamsplitter was adequette.
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