Help needed with my ETX-90

[DennyD]

Anyone in the Northern California/Sacramento area who can help me with my Meade ETX-90? The secondary mirror has moved a little on the baffle. I understand this is common on the older ETX-90 versions like mine and I don't want to send it to Meade. Thank you. Denny. 

[Alan64]

The secondary-baffle is glued over and round the mirror.  It sounds as though the baffle has either come loose or has slowly shifted off-center...

https://i.imgur.com/c1wgrNY.jpg

You want to work in as dust-free an environment as possible.  Great pains must be taken not to soil the mirror, and to apply whichever adhesive that would be suitable sparingly yet thoroughly.  You don't want the adhesive to spread over and onto the edge of the mirror, nor onto the meniscus outside the baffle.  Be certain to remove the old adhesive from the baffle and the area of the meniscus surrounding the mirror.Be certain to remove the old adhesive from the baffle and the area of the meniscus surrounding the mirror.  The surfaces to be joined should be clean, grease- and oil-free.

Incidentally, the secondary-baffles of these commercial Maksutovs are configured for daytime/terrestrial use.  For nighttime/astronomical use, the baffle should be reduced in height.  That would also reduce the diameter of the secondary-obstruction, which would increase contrast and sharpness.  Re-blackening/flocking the baffles within would also help in improving the contrast even further.  You may or may not wish to pursue that.  I will be, myself, as this is the flared secondary-baffle of my 127mm Maksutov...

...and it's begging for a reduction. 

Edited January 6, 2020 by Alan64

[Peter Drew]

The complete front cell and corrector unscrew.  At a pinch, you can carefully warm the secondary baffle with a hairdryer and when the glue softens slightly you can carefully slide the baffle back to its correct position.  I've had to do this on the Meade 7" Maksutov.    🙂

[Alan64]

I have to wonder if there would be any need to mark the position of the meniscus in relation to the optical-tube, and for that particular telescope.

Then, in the next moment, I have to wonder if a glue immune to creeping might be used, like 5-minute epoxy.

In the end, I'd rather a more permanent solution.

Edited January 6, 2020 by Alan64