Newbie here – Meade ETX 90

[kaslonpro]

I am excited to join this big star gazing community! I realize I am abusing of your kindness, so that you in advance for any help you can give.

I have an old telescope, what appears to be a Meade ETX 90 from the early 2000s. I cleaned it pretty well after many Youtube videos and online research. I found full blown spider webs and dead spiders!

I have encountered a few of issues as I'm putting it back together and I wonder if anyone might be able to help.

1. I took off the screws of the back of my OTA (I know I shouldn't have!) and now I'm not sure how to put them back on (see attachments). When I try it seems to push the primary mirror instead of fastening to anything. 

2. My secondary mirror flip is broken, the plastic piece part fell off. Is it possible to fix? The mirror itself is also very dirty (see attachments) and I don't think it can be cleaned further. Any tips on how to replace it and where to buy the parts? Or is it possible to not use the 90 eye piece viewport and instead use the front one so I don't need to fix the flip or the mirror?

4. My secondary baffle is sliding off. I've read that this is a problem w/older models. I tried pushing it to the right place and it requires some force, but after 1 minute it slides back to its original place. What should I do? Does this matter?

5. The plastic attachment to hold the smaller lens (finderscope?) wobbles no matter how tightly I screw it on. I don't know if it has anything to do with the front plastic part being a little broken.

Thank you for your help in advance, and I am still learning terminology so be easy on me

 

 

Edited September 4, 2020 by kaslonpro

[RT65CB-SWL]

Hi @kaslonpro and welcome to SGL. 

1. The screws that you are pointing at are one half of the collimation screws. The ones next to them are the other half. 
   (I think the dome/pan-head screw is the 'adjust' and the recessed screw is the 'lock'). The holes nearest the outside edge are the ones
   for reassembly of the ABS back to the OTA. From memory, I think they are 6/32 UNC if you need to replace these, though I am not
   sure what the collimation screw threads are.
2. Remove the flip-mirror assembly and shaft and purchase an ETX to SCT adaptor ring and visual back (shown below).
   I use a 1.25" and/or 2" visual back + star diagonal & SCT accessories with my ETX105. 
   CAUTION: if you are using your ETX90 with an adaptor ring, 1.25" visual back & star diagonal, you may not reach the zenith; (i.e. directly
   overhead); as it may/will collide with the base of the fork mount.
3. ?
4. If you are referring to the baffle on the meniscus cell? - then yes it needs to be fixed. I don't know how to or what to recommend... sorry! 
   I have included a couple of internet links at the end that maybe of use to you and other ETX users.
5. I would not worry to much about the finder bracket, unless the supplied finder is the 90deg, one, (it was a minor improvement).
   I have the straight through/inline one, and as I am left-eye dominant, it did not work for me, as it is mounted on the left side. I have attached
   two lightweight universal metal bases/brackets; (image below); with 3M double-sided tape for an RDF or finderscope.
   I am going to reposition them either side of the dovetail bar the nearer the front end.

<--- the universal metal base/bracket for RDF/finderscope via AstroBoot.

Below are some images of my 're-modded' ETX105...

The jubilee/hose rings hold the OTA to the dovetail bar as I cannot find compatible diameter tube rings...
"Vorsprung durch non-Technik".

An extremely useful website for all things ETX related is... http://www.weasner.com/etx/menu.html
...and for repairs, maintenance, tune-ups, etc., I would recommend... http://sctelescopes.com/ 
...assuming you are living/residing in GB/UK 🇬🇧 

Edited September 5, 2020 by Philip R

[kaslonpro]

You are so kind. Thank you. I don’t know if I understand all the lingo. I just don’t understand why they won’t screw in, 3 of the inner ones will but others just seem to just push the back of the ota forward rather than screw into it. 
Oops I ended up merging 2 and 3 but forgot to fix the numbering. 
 

I guess at this point if that baffle is off I wonder if it’s better to just try and buy a new scope. So much work for this one and I don’t even know if it’ll even work 🤨

 

thank you again! 

Edited September 5, 2020 by kaslonpro

[RT65CB-SWL]

6 hours ago, kaslonpro said:

You are so kind. Thank you. I don’t know if I understand all the lingo. I just don’t understand why they won’t screw in, 3 of the inner ones will but others just seem to just push the back of the ota forward rather than screw into it. 
Oops I ended up merging 2 and 3 but forgot to fix the numbering. 
 

I guess at this point if that baffle is off I wonder if it’s better to just try and buy a new scope. So much work for this one and I don’t even know if it’ll even work 🤨

 

thank you again! 

I think another SGL'er had a similar issue with his/her Maksutov or SCT secondary and removed and cleaned it up, then re-stuck it in position with a very thin layer of adhesive after a few 'dry' runs. I am not sure what adhesive he/she used, but if you decide to re-stick the secondary, I would...

1. Mark a position on the meniscus cell and tube with a piece of masking tape or self-adhesive label and place a few index marks with a pen or pencil and cut through it the label before unscrewing. This will make to easier to realign during during reassembly.
2. If you do remove the front element and decide to stick it with adhesive, my advice here would be to leave the cell off for a few weeks. Some adhesives, (i.e. some cyanoacrylates), do release some vapour while curing/drying even after a few days. This may cause a small area of the glass to have narrow 'foggy ring' around it and you don't want that spoiling your views through the eyepiece.  
3. DO NOT remove the meniscus element from the cell by unscrewing the retaining ring - note: this is the one with the writing, as in your first image.
4. Re-assemble and connect the OTA to the rear ABS plastic housing and it should be good to go!

 

I noticed you said in your first post of this topic, quote: 

14 hours ago, kaslonpro said:

....

2. My secondary mirror flip is broken, the plastic piece part fell off. Is it possible to fix? The mirror itself is also very dirty (see attachments) and I don't think it can be cleaned further. Any tips on how to replace it and where to buy the parts? Or is it possible to not use the 90 eye piece viewport and instead use the front one so I don't need to fix the flip or the mirror?

Can you submit an image of the flip mirror assembly? - as I think your second image is the mirror itself! - what did you clean it with?

My ETX flip-mirror assembly got damaged, along with two of the three mounting points and a long crack in the ABS plastic cell after the OTA fell from one of my mounts when the cast-metal dovetail mounting snapped. (fortunately or luckily it was on grass/lawn). I have kept the mirror as it may come in use; (though I may sell it as I no longer have a use for it), and is in a VGC and clean condition and kept in a dust free bag in a drawer. 

I had a local engineering workshop make the replacement aluminium backplate. When fitted for the first time, it did not require collimating or other adjustments. Over the years since the 're-mod' my ETX105 has had one clean, collimated and service by SCTelescopes.