Meade ETX125 - How to remove front lens

[bendiddley]

I have a Meade ETX125 that has some mold growth on the inside of the front lens which I would like to clean but I don't know how to take it apart to get to it, does anyone know? Cheers, Ben

[Ben the Ignorant]

Hi, other Ben. My C5 has that type of ring, I made this tool to unscrew it; just a slab of woob with two holes and two dull nails:

 

[Ben the Ignorant]

I just remembered I bought thermo-shrink tubes a long time after I made this tool, it would be more prudent to wrap the nail tips in that soft plastic, or a short piece of electrical wire skin would do, too.

[RT65CB-SWL]

Hi @bendiddley

Read carefully... 

1. make a tool like the one shown by @Ben the Ignorant
2. mark a position on the meniscus cell and outer ring. (the reason for marking the meniscus cell and outer ring is that the ETX's are collimated during production/manufacture so they are aligned before shipment).
3. carefully unscrew the retaining ring with the tool, (this is the one with the writing).
4. when completely undone and free, find a piece of stiff card and other dust free material and place on top.
5. carefully turn the OTA, etc, so the visual back is pointing up and carefully withdraw the OTA.
6. when you have cleaned the 'mould' / 'fungus' (I used Baader Wonder Fluid & cloth on my ETX105) from the meniscus cell on mine. Do not apply heavy pressure and wear disposable gloves otherwise you end up with finger prints too!
7. reassembly is in reverse order and ensure the marks you made earlier line up.

If you do not feel confident, I would recommend you 'phone Steve @ SCTelescopes a call and arrange a visit. (takes about 90minutes from Reading by car via A329(M)/M4/M25).

If you are not a member of Reading Astronomical Society, (www.readingastro.org.uk), please feel free to visit this Friday evening (24th Nov '17) meeting from 7:30pm to the Astro Basics section. I will be there.

DISCLAIMER: 

• If you are confident, proceed at your risk, not mine. I will not accept any insurance claim(s) or claim(s) for damages, misuse, neglect, etc., to you or any other person(s), your 'scope and/or accessories whilst carrying out any modifications or use in any country/nation and/or territory of the parent country/nation.   

 

PS... I will send you a PM with my mobile 'phone number if you would like further info etc.  

 

[bendiddley]

Thanks Guys. Philip I'm not quite sure what you mean by 'make a mark on the meniscus cell and outer ring' what is the meniscus cell and outer ring and why do I need to mark it, can you clarify/elaborate? Also when the retaining ring is off and I turn the OTA upside down how does the OTA come out, does it just slide out and what exactly is coming out, is there like an inner part of the OTA that slides away from the blue OTA outer shell or something?

[RT65CB-SWL]

The meniscus cell is the glass that holds the secondary mirror.

...does the picture make it any clearer?

To 'mark' it means, so the meniscus cell goes back as it was when it was fitted, so as not to lose the collimation. I did see a YouTube of someone disassembling and re-assembling an SCT and he 'marked' the corrector plate and outer ring with a chinagraph pencil or something like that.

The ETX90/105/125 are not the easiest of instruments to collimate as it involves removing the OTA from the plastic rear-cell flip mirror assembly. 

Let me know if you can make this Friday evening and I will explain or ask someone. I will bring mine too... if I remember! - I forgot to attend last Saturday's main meeting. 

[RT65CB-SWL]

@bendiddleyIf you have not checked this site out... http://www.weasner.com/etx/menu.html I recommend it. Due to personal issues Mike no longer updates it. It has got to be the most informative site to anything ETX related.  

[bendiddley]

All sorted now, thanks to Phils advice.