Removing and reinstalling meniscus

[Robindonne]

my right knee hurts so much that i decided to remo…
No actually a question about a maksutuv. 

I kind of understand that the optics of a refractor cant be removed from its cell without the need of precise  aligning/adjusting afterwards.  But how does this work with the meniscus of a Maksutov?  I need to remove the meniscus for some maintenance. I can carefully try to mark both items if necessary.  I think, not sure, that the secondary is collimatible but the meniscus cant be adjusted once its mounted.  
Is it safe when done carefully? Or is it always needed to send it afterwards to a professional for alligning?

Edited June 19, 2021 by Robindonne

[Avocette]

Take a look at the thread from @Captain Magenta about reverse engineering his Maksutov-Cassegrain (SkyMax 180).

[Robindonne]

1 minute ago, Avocette said:

Take a look at the thread from @Captain Magenta about reverse engineering his Maksutov-Cassegrain (SkyMax 180).

Yes thanks.  I read it twice but i dont remember the removal of the glass was mentioned.  But ill go over it again.  I might have missed it.   Thanks again

[Captain Scarlet]

I did remove the glass, though I'm not sure if I documented it. I pulled off the baffle because it was seriously off-centre, but that in itself didn't require wholesale removal of the glass plate IIRC. I did eventually decide though to check that the clips retaining the glass in place were not "metal clip directly on glass", and found that that was in fact the case, so I did remove the glass to insert thin pieces of electrical tape under the clips. Recollimation was fine.

I think all the surfaces at that end are spherical, and there is very little scope (apols for pun) for lateral movement of the glass, so the process of glass-removal and replacement is pretty forgiving. The thing you should take care of, if you are concerned, is to ensure the central reflective spot goes back in properly centred. I'm not actually sure how much care they took in ensuring that at the factory anyway, given how badly my baffle had been placed.

All in all, you should be fine I think. The glass is coated with SiO2 (i.e. Quartz crystal, very hard indeed) so will be extremely scratch-resistant. I re-glued and removed my baffle (using Acetone) about 4 times I think before I was totally happy. Use superglue, it's totally soluble in Acetone.

Good luck and keepus informed!

Cheers, Magnus

[Robindonne]

Hello Magnus. Was just carefully reading all the text again from your reversed engineering post (for the third time😅). I didn’t find it documented indeed.  

4 minutes ago, Captain Magenta said:

The thing you should take care of, if you are concerned, is to ensure the central reflective spot goes back in properly centred.

This one is something to pay extra attention to when i remove the retaining ring.  Thanks. 

It does have some cork between that retaining ring and the glass, but i wasnt sure if these pieces of cork were part of an alignment or just to have a soft connection between the ring and the glass. And the way the glass (and so the reflective center) is centered will be visible when i remove that retaining ring.  
 

Yes i’ll post some pictures when all is finished, or maybe during this work when im stuck😬.  
 

thanks for replying and thanks for your initial reversed engineering post.  Threads like that are forever helpful. 

[RT65CB-SWL]

On 19/06/2021 at 22:44, Captain Magenta said:

…

I think all the surfaces at that end are spherical, and there is very little scope (apols for pun) for lateral movement of the glass, so the process of glass-removal and replacement is pretty forgiving. The thing you should take care of, if you are concerned, is to ensure the central reflective spot goes back in properly centred. I'm not actually sure how much care they took in ensuring that at the factory anyway, given how badly my baffle had been placed.

…

I read somewhere that they do need to be properly centred too. I cannot remember whether it was via Meade’s website or Mike Weasner’s ETX website.

When my ETX105 had a minor bump (falling of a mount and damaged the rear plastic rear flip mirror cell housing and a cheap plastic star diagonal), the meniscus cell had ‘moved’ slightly. Luckily no other damage to the primary mirror and the secondary/centre spot/baffle had not detached or became misaligned on impact.

Maksutov OTA’s can be collimated by the end-user by adjusting the push/pull screws on the rear For the ETX90/105/125 it involves removing the flip-mirror housing. It takes a bit longer to do than an SCT or ‘Newtonian’ reflector. I use two laser collimators (a Baader and a HoTech), an artificial star tool and a collimating cap.

  

Edited June 23, 2021 by Philip R