Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

ETX 125 questions

  • Please log in to reply
14 replies to this topic

#1 toucansam

toucansam

    Sputnik

  • *****
  • topic starter
  • Posts: 34
  • Joined: 18 Jun 2018

Posted 26 June 2019 - 07:20 PM

I had an ETX90 for a little while and liked it a lot, ended up giving it to my son so he could use it with his DSLR.

 

I have a 90mm Orion that I have been using as a replacement, but have wanted to step up to a 125mm or 127mm and give the Orion to my folks for terrestrial use.

 

A member had an ETX 125 at a great price, so I picked it up.  Looks to be in good shape overall. 

 

Only issue is that the plastic housing that the OTA sits in rotates 90 degrees.  Pulling it back towards the observer, it does not come off the OTA, at least not with the amount of force I've applied thus far.  But the entire OTA rotates inside of the plastic rear assembly.  Wondering if this will be an issue, and how to fix.  My ETX90 definitely did not do this.

 

This unit is deforked.  Is there an easy way, that is not quite as permanent as cement or industrial adhesive, to adapt a standard finder scope to it?  The factory clip-in finder scope location is empty, and looks less than strong anyway, as far as using it to mount a more traditional finder.

 

Finally, I had been using the Orion with an AZ-GTi mount, and would love to put the 125 in its place.  However, the ETX has a built-in diagonal that does not rotate.  It does have a threaded hole at the rear, for a 45 degree diagonal generally.  Is there an adapter I can buy that will thread onto that location and then provide a standard mounting tube for a traditional 90 degree diagonal, so I can mount the ETX (essentially sideways) to the AZ-GTi and still use eyepieces from a comfortable head position?

 

Thanks to all.



#2 toucansam

toucansam

    Sputnik

  • *****
  • topic starter
  • Posts: 34
  • Joined: 18 Jun 2018

Posted 26 June 2019 - 07:38 PM

Took it apart, figured it out.  Inner sleeve that threads in and holds the mirror was loose.  Looks like I need to clean the internals anyway, that will be interesting as I've never tried it before.

 

Looks like maybe rings will work as far as orienting the telescope such that I can use the built-in diagonal, or buy a few parts and use the rear port.  More research needed.

 

Couple of finderscope options popped up too.  Only problem is I need to keep the entire thing under the weight that the AZ-GTi can handle.



#3 Boom

Boom

    Messenger

  • *****
  • Posts: 436
  • Joined: 11 Jan 2008

Posted 26 June 2019 - 07:49 PM

The pricey, nice way to get rid of the built in flip mirror would be to buy a Wegat rear plate.

http://wegatoptical.com/shop/

This screws onto the back of the OTA and you can mount an SCT VB onto it.

The cheaper way is to use an adapter that allows you to mount an SCT VB onto the existing rear port behind the flip mirror.

https://www.highpoin...6hoCBMMQAvD_BwE

or purchase an ETX port VB

https://www.amazon.c...e/dp/B00HBU28CA


Keep in mind that optimal focus is achieved using the built in flip mirror. Using a diagonal behind the rear port would increase your back focal distance and introduce spherical abberation. If you don't want to introduce error, your only option is to get the Wegat.

Edited by Boom, 26 June 2019 - 07:53 PM.

  • Don Taylor and halx like this

#4 SeattleScott

SeattleScott

    Fly Me to the Moon

  • *****
  • Posts: 6091
  • Joined: 14 Oct 2011

Posted 26 June 2019 - 10:35 PM

Can always get a Rigel and stick it on there for a finderscope. Light weight so shouldn’t cause balance issues.

Scott

#5 25585

25585

    Fly Me to the Moon

  • *****
  • Posts: 5857
  • Joined: 29 Aug 2017
  • Loc: In a valley, in the UK.

Posted 28 June 2019 - 12:56 PM

I am attracted to this Meade zs its in a fork mounting, the only 125mm MCT that is. How does its Goto system compare with Celestron and Sky Watcher and Orion?



#6 Okcman

Okcman

    Explorer 1

  • *****
  • Posts: 53
  • Joined: 01 Dec 2016
  • Loc: Oklahoma City, Oklahoma

Posted 28 June 2019 - 06:02 PM

Toucan Sam - I too recently acquired a Meade etx 125 too - and i cleaned the primary mirror  in situ  - I cleaned mine by first removing the optical back/ flip mirror - I had to also remove the set screw to the focuser and set it aside - the main tube covering the stem and the primary mirror can easily be removed by unscrewing counterclockwise - if I remember right - the conundrum is not to knock or bump the primary mirror - as a deforked unit it might be a slight disadvantage for this procedure - I used the suggested tried and true distilled water and denatured alcohol and a drop of dawn soap - I used squirt bottles from harbor freight and prepared  3 bottles of the formula to wash the primary mirror - mine sufferd from outgassing - I used qtips to gently daub the persistent grease - but only once and the were discarded and new one to daub another spot - I probalbly broke several tenants of doing no harm but  my primary optics are really clean



#7 toucansam

toucansam

    Sputnik

  • *****
  • topic starter
  • Posts: 34
  • Joined: 18 Jun 2018

Posted 01 July 2019 - 05:38 PM

I disassembled the scope for cleaning, and I must say, looking at the TINY pieces of metal that are pushed, clip-style, onto the rims of the plastic holes where the 1.25" adapters go, leaves me speechless.  I'm not sure how much weight I want to trust to either of those two spots.

 

The spherical abberation issue worries me.  If I go with an aftermarket back plate, just how bad will it be?

 

Thanks.



#8 Boom

Boom

    Messenger

  • *****
  • Posts: 436
  • Joined: 11 Jan 2008

Posted 01 July 2019 - 06:05 PM

I disassembled the scope for cleaning, and I must say, looking at the TINY pieces of metal that are pushed, clip-style, onto the rims of the plastic holes where the 1.25" adapters go, leaves me speechless.  I'm not sure how much weight I want to trust to either of those two spots.

 

The spherical abberation issue worries me.  If I go with an aftermarket back plate, just how bad will it be?

 

Thanks.

 

I think you misunderstood.  Installing a Wegat backplate combined with an SCT visual back and diagonal will result in the smallest change in light path compared to the stock internal flip mirror system.  The Wegat replaces the entire plastic flip mirror assembly and bolts directly to the existing backplate (the one with all the collimination screws and grease pencil writings) of the OTA.

 

If you choose to mount a diagonal onto the existing rear port, i.e. the port under that black aluminum cover next to the flip mirror levers, you are surely going to increase the light path by a significant amount.  How much will this impact the spherical correction?  I don't know, but it should be minimal.  You can try jury rigging a diagonal there first and do some star testing to find out?

 

The Wegat plate is the best, albeit expensive solution.  This way you can even use 2 inch EPs.


Edited by Boom, 01 July 2019 - 06:16 PM.


#9 toucansam

toucansam

    Sputnik

  • *****
  • topic starter
  • Posts: 34
  • Joined: 18 Jun 2018

Posted 01 July 2019 - 06:14 PM

Roger.

 

That makes sense.

 

I went to Wegat's site and looked at the product.  Just trying to justify the expense considering it about what I paid for the scope in the first place, ha.



#10 cytan299

cytan299

    Viking 1

  • *****
  • Posts: 655
  • Joined: 24 Nov 2014

Posted 01 July 2019 - 06:23 PM

And by drilling holes on the Wegat plate, you have easy access to the collocation screws. That’s what I did or else collimating my ETX125 would not have been impossible (or at least very difficult). IMO, the Wegat is well worth it.

 

cytan



#11 Boom

Boom

    Messenger

  • *****
  • Posts: 436
  • Joined: 11 Jan 2008

Posted 01 July 2019 - 06:23 PM

For sure.  Unless I knew my copy had a killer set of optics (such as this one http://fidgor.ru/Obs...2/test_412.html), I wouldn't invest in that kind of money on such an old scope.



#12 toucansam

toucansam

    Sputnik

  • *****
  • topic starter
  • Posts: 34
  • Joined: 18 Jun 2018

Posted 01 July 2019 - 06:38 PM

For sure.  Unless I knew my copy had a killer set of optics (such as this one http://fidgor.ru/Obs...2/test_412.html), I wouldn't invest in that kind of money on such an old scope.

 

 

I'm afraid I don't have any idea what is going on on that page.



#13 halx

halx

    Vendor (DSO Planner)

  • ****-
  • Vendors
  • Posts: 1811
  • Joined: 28 Sep 2010
  • Loc: Albany, California, USA

Posted 01 July 2019 - 07:07 PM

When I've been poking that EQ mount idea for my ETX125, I've decided to use the rotation in the rings to orient the stock diagonal. The OTA is very smooth and perfectly cylindrical so it looked trivial to make rings that would allow an easy, safe, and smooth rotation with a single lock clutch. It's even easier to implement now (like 15 years later) when I have a 3D printer at home... But I got rid of my EQ mounts grin.gif


Edited by halx, 01 July 2019 - 07:10 PM.


#14 toucansam

toucansam

    Sputnik

  • *****
  • topic starter
  • Posts: 34
  • Joined: 18 Jun 2018

Posted 01 July 2019 - 07:35 PM

I'm looking for rings now.


Edited by toucansam, 01 July 2019 - 07:35 PM.


#15 toucansam

toucansam

    Sputnik

  • *****
  • topic starter
  • Posts: 34
  • Joined: 18 Jun 2018

Posted 01 July 2019 - 08:02 PM

I like this idea best so far:

 

https://www.cloudyni...ification-r2811

 

The Wegat has a 2" diagonal capability.... But the ETX won't make full use of that aperature, correct?




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics