Beam splitter optics problem?

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Zuul
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Beam splitter optics problem?

#1 Post by Zuul » Fri Jul 17, 2020 10:56 pm

I’m continuing to clean up and fix my Microstar IV. There is a strange spot/smudge visible on the teaching bridge‘s 1st prism. I don’t know if this is some neuance of the optics or damage to a coating ... or if it harmless or detrimental to the image. This is where the pointer resides, so is there a possibility that the spot is from that? I’m discovering that most of my objectives have problems of some sort, so it’s not easy to point to flare or blurring or vignetting and confidently attribute it to this aperant defect.
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hans
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Re: Beam splitter optics problem?

#2 Post by hans » Sat Jul 18, 2020 1:21 am

I see some small areas of degradation near the edge of the metallized area inside the splitter on mine but I still get a clear view through most of it. On both of ours it does appear to be something specific to the metallization, rather than a more general case of delamination along the 45 degree joint of the splitter.
splitter-degradation.jpg
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Zuul
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Re: Beam splitter optics problem?

#3 Post by Zuul » Sat Jul 18, 2020 1:36 am

I know photos can hide things, but I’d say that looks completely different than mine. :(

hans
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Re: Beam splitter optics problem?

#4 Post by hans » Sat Jul 18, 2020 2:19 am

Yeah, hard to interpret the photos, took a quite a bit of fiddling just to get a decent photo of the internal surface. In person mine basically looks like an elliptical half-silvered mirror floating unsupported in the middle of the splitter cube at a 45 degree angle. On yours, does the inner spot still function like a splitter? Or the outer ring? Or neither?

Zuul
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Re: Beam splitter optics problem?

#5 Post by Zuul » Sat Jul 18, 2020 2:35 am

Both heads have a completely formed image. I’ve only had the camera on the “far” head. Since I’ve been trialing different camera set-ups, I’ve been assuming any aberations are related to that. I’ll need to swap heads and see what there is to see.

MichaelG.
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Re: Beam splitter optics problem?

#6 Post by MichaelG. » Sat Jul 18, 2020 6:45 am

Zuul wrote:
Fri Jul 17, 2020 10:56 pm
I’m continuing to clean up and fix my Microstar IV. There is a strange spot/smudge visible on the teaching bridge‘s 1st prism.
.

If I am interpreting your photos correctly, that looks like a patch of mould
... which may clean off, or may have caused etching of the surface
The black patches like we see on window glass are relatively harmless, but some growths can introduce chemical etching of glass and/or coatings.

Close inspection of your surfaces is required, I think

Here’s a short article: https://www.ncbi.nlm.nih.gov/pmc/articl ... 46_028.pdf

I was never actively involved in the analysis of the results, but [decades ago] did run some ‘mould growth’ tests on military optics.


MichaelG.
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hans
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Re: Beam splitter optics problem?

#7 Post by hans » Sat Jul 18, 2020 7:10 am

MichaelG. wrote:
Sat Jul 18, 2020 6:45 am
If I am interpreting your photos correctly, that looks like a patch of mould ...
For what it's worth, I was leaning toward interpreting Zuul's photos the other way around -- the black batch being a relatively clear view through the splitter to a dark background and the surrounding cloudy brownish ring being an advanced stage of the same deterioration I am starting to see around the edge of mine.

Zuul
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Re: Beam splitter optics problem?

#8 Post by Zuul » Sat Jul 18, 2020 2:25 pm

hans wrote:
Sat Jul 18, 2020 7:10 am
For what it's worth, I was leaning toward interpreting Zuul's photos the other way around -- the black batch being a relatively clear view through the splitter to a dark background and the surrounding cloudy brownish ring being an advanced stage of the same deterioration I am starting to see around the edge of mine.
Yes, that is a good way to describe it. My initial reaction was that a partially mirrored mirrored surface had been “worn away” it the center. Another way to describe how it looks would be to imagine glass fogged by your breath with the center cleared by a single finger print.

MichaelG.
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Re: Beam splitter optics problem?

#9 Post by MichaelG. » Sat Jul 18, 2020 2:37 pm

.

Sorry, my misunderstanding ... I thought the black was the troublesome patch.
There is a strange spot/smudge visible
MichaelG.
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Zuul
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Re: Beam splitter optics problem?

#10 Post by Zuul » Sat Jul 18, 2020 3:05 pm

MichaelG. wrote:
Sat Jul 18, 2020 2:37 pm
.

Sorry, my misunderstanding ... I thought the black was the troublesome patch.
There is a strange spot/smudge visible
MichaelG.
I don’t know enough to say if the central area is the optic’s original condition or degraded, so I left the interpretation open. The area is transparent, though, which isn’t immediately obvious in the photos depending on perspective. It is something of an optical illusion.
Image

I appreciate any input, and read the linked information, nonetheless.

Zuul
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Re: Beam splitter optics problem?

#11 Post by Zuul » Sat Jul 18, 2020 6:10 pm

Images captured through both ends of the bridge and then without the bridge clearly show that this is absolutely degrading the view. Quite a lot, actually. The most obvious effect is a severe vignetting, but no doubt it goes beyond that. It visible on both heads, though not equally.

I guess I might as well open it up and see which surface it is.

MichaelG.
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Re: Beam splitter optics problem?

#12 Post by MichaelG. » Sat Jul 18, 2020 7:20 pm

Zuul wrote:
Sat Jul 18, 2020 3:05 pm
I don’t know enough to say if the central area is the optic’s original condition or degraded, so I left the interpretation open. The area is transparent, though, which isn’t immediately obvious in the photos depending on perspective. It is something of an optical illusion.

I appreciate any input, and read the linked information, nonetheless.
.

Understood ... Thanks
... wishing you the best of luck with whatever you discover.

MichaelG.
Too many 'projects'

hans
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Re: Beam splitter optics problem?

#13 Post by hans » Sat Jul 18, 2020 11:14 pm

I just noticed one of my heads also has some degradation of the 45 degree internal surface of the splitter. Seems like maybe Reichert had some persistent issues with the quality of their splitters?
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Zuul
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Re: Beam splitter optics problem?

#14 Post by Zuul » Sun Jul 19, 2020 1:28 am

When I opened mine there was evidence of water intrusion. (I hope it was water!) I think that may have cause the silvering to oxidize from the edges in.

hans
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Re: Beam splitter optics problem?

#15 Post by hans » Mon Jul 20, 2020 5:17 am

Weird, mine also has what looks like some sign of liquid inside. It is fully disassembled now, if there is anything you want photos of for comparison.
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bridge-liquid-2.jpg
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apochronaut
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Re: Beam splitter optics problem?

#16 Post by apochronaut » Mon Jul 20, 2020 3:59 pm

One of my Diastars came with 6 of those. That one is like a Hydra but some of them are like a Hurling roster. Miller has been selling one for a while with I think 14 heads on ebay. It comes with an optional usher.

I can pilfer an optical section to substantially cut shipping down, if you want to repair yours. It's just 4 screws.

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