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How to collimate a reflector lens

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#1 jmstonge

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Posted 02 December 2020 - 04:46 PM

I bought an old vintage Russian lens, known as the MTO 11CA, although the photos of it does not seem to match exactly like other MTO 11CA.

 

I noticed that the lens is out of collimation. I have a Canon Eos M attached via EOS M to M42 adapter, and can see that there is a vague double image in the vertical axis on the best focus. Is there any good way to collimate the old Reflector lens? Any help would surely be appreciated. I can take some photos later if anyone needs to see exactly which one it is if necessary. 



#2 ngc7319_20

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Posted 02 December 2020 - 05:44 PM

Is anything loose in the lens?  Does it rattle?  Double image is slightly hard to understand, unless it is thermal issue -- was the scope allowed to acclimate?

 

Read up on how to use a Cheshire eyepiece for refractor collimation.  Probably could use one of the Celestron collimation eyepieces.  There was an old version you could probably get for couple $ or this newer one for $40 or so.

 

https://agenaastro.c...tors-94182.html



#3 jmstonge

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Posted 05 December 2020 - 12:47 PM

Thank you for your reply. 

I actually found a website that explained a bit more about my lens, and I was also mistaken, the specific model I have is the MTO 1000A. 

http://www.stricklin...ne.htm#relaxing

I found out the reason for the astigmatism/double image is due to over tightening of the spring ring that keeps back primary mirror in place. I loosened it as much as possible to where the back mirror was still secure and that seemed to have corrected my problem. 

 

I am stuck with cleaning of the front element. The front notched lens retaining ring is stuck and I have had no success with my lens spanner. Any suggestions, aside from using a drummel to take it off, as this part would be to scarce to replace.  

 

I am also putting together a small guide on the disassembly of this particular model of lens, is there a place where people post such information?



#4 ngc7319_20

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Posted 05 December 2020 - 05:51 PM

 

I found out the reason for the astigmatism/double image is due to over tightening of the spring ring that keeps back primary mirror in place. I loosened it as much as possible to where the back mirror was still secure and that seemed to have corrected my problem. 

 

I am stuck with cleaning of the front element. The front notched lens retaining ring is stuck and I have had no success with my lens spanner. Any suggestions, aside from using a drummel to take it off, as this part would be to scarce to replace.  

 

I am also putting together a small guide on the disassembly of this particular model of lens, is there a place where people post such information?

OK -- severe over-tightened mirror makes sense on the double image.

 

Look at the front retaining ring with a magnifier.  Sometimes there is a drop or 2 of glue on it.  I do not have specific knowledge of this scope, but it is often the case that there is glue.  I have usually been able to dissolve it with couple tiny drops of 91% rubbing alcohol.  Acetone or lacquer thinner will also work.  These may damage paint, so be careful.   Also if you do not have a high-quality spanner, getting one may help.  You can put more force if the spanner tangs engage well with the lens ring.  Sometimes helps if a second person holds the lens body.  Wear high-grip gloves.

 

Not sure about posting guide.  You could probably just post it here, though you will be limited on photo size per each post.  Maybe use multiple postings to get around the limit?  Google search seems able to find postings here.  I looked around internet a bit but did not see any central collection for this lens.  There are a lot of articles on its performance, but they are scattered to different photographic websites.



#5 jmstonge

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Posted 06 December 2020 - 03:29 PM

I will have to find a nice magnifying glass and take a look. I do have just a cheap spanner, any particular brand that would be recommended? I will try the isopropyl alcohol to see if that helps loosen things up. I am concerned that someone may have cross-threaded it in the past, as one side sees closer to the outer casing the the other. Thanks again for your suggestions. 




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