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Early Unitron 128 clean-up with objective issues

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#1 shredder1656

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Posted 14 September 2018 - 07:58 AM

Not going to be a deep and/or long thread.  I couldn't think of what to call it, so here it is.  

 

Picked up a sweet little Unitron 128.  Appears to be an early version.  Looks pretty good, except the objective was very cruddy.  

 

So...did I screw up here?  I did not want to split the elements, but it was worse than the picture.  I disassembled, did a little huff and puff with a squeezable puffer, and then soaked the elements in peroxide overnight.  After that, I rinsed them off with distilled water, and let them air dry.  I then noticed all of the spots shown in the photos.  

 

The star-shaped marks, I assume, are the results of the fungus etching the class.  But, what are the other rectangular marks?  Is that coating damage?  If it is, how would that have occurred?  No touchy by me until after the soaking.  Would peroxide cause this?  

 

Also, before disassembly, the Newton rings looked like whorls on a fingerprint, rather than concentric circles.  After assembly, new spacers, and nearly myriad re-positions, the rings are about as good as I can get.  They are not centered, but are at least round.  The cell design seems to be counter-productive to secure and perfect centering and spacing.  Any input?

 

Other than this, it is coming along nicely.  It is a sharp looking little scope.  I just hope the images are not severely affected.  I am sure that it will have an effect, but hopefully minimal  

 

20180914_084637.jpg 20180914_082746.jpg 20180914_082705.jpg 20180914_082539.jpg

 

 


Edited by shredder1656, 14 September 2018 - 08:00 AM.

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#2 rolo

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Posted 14 September 2018 - 08:15 AM

Coating damage, shouldn't affect much of anything if any.


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#3 DAVIDG

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Posted 14 September 2018 - 08:52 AM

 With the interference  rings being way off that shows that the air gap is not uniform. First the spacers need to positioned at  a 120° centers and they also need to be the same distance from the edge.  Don't guess, make a drawing to place the lens over it to get them in them in the correct position. When you place the lens back in the cell the spacers should be position so they are next to each screw that holds the retainer ring on. Also you should improve the cell by placing a small piece of tape on the rear surface of the cell that the lens rest against right next to the screws.so they are at 120° centers as well. Now the lens has three defined points of contact and those points provide equal pressure on the spacer. The upper retainer ring should also have three taps placed on it that match the position of the ones on the bottom.  What you have now is the lens resting on three points of contact with the spacers over these points and then the retainer ring also have three points of contact over the spacers. Now when the retainer ring is tighten down it applies even pressure on the glass and on the spacer so the air gap is uniform and the interference ring should be round and centered.

 

                    - Dave 


Edited by DAVIDG, 14 September 2018 - 09:04 AM.

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#4 shredder1656

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Posted 14 September 2018 - 09:03 AM

Thanks, rolo.  I was assuming that the coating loss would not be a significant negative.  The etching is more of my concern.  

 

Could the peroxide have caused the loss, or is it just from some previous issue?

 

DavidG, thank you.  I actually did draw a template to replace the spacers.  However, the suggestion to make the 3 points of contact in the cell was not done.  Great suggestion, and I will do that asap.  



#5 DAVIDG

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Posted 14 September 2018 - 09:12 AM

  The coating was damaged by the fungus so the peroxide didn't damage the coating.  When you look that the picture showing the interference rings you see  that they are smaller arc and wider apart on  the left side. That shows that the two elements are closer together there. The air gap is thinnest at that point and widest on the right side. So the spacer on the right side is either thicker then the other two, placed closer in,  there is less pressure on the lens at that point or some combination to cause the wider space. 

 

                 - Dave 




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