Review - ADM Dovetail Plate and Mounting Rings
Posted: 10 July 2016
I have used a Meade ETX-105PE telescope for 11 years, seen at the left below on the observatory patio in August 2009. Unfortunately, after years of reliable use the Declination motor failed in June 2016.
There were two options to be considered as I wanted to continue using the telescope. I could either try to have the problem corrected or I could mount the ETX-105 OTA (Optical Tube Assembly) on my 13+ year old Meade LXD55 German Equatorial Mount (GEM). After confirming that the LXD55 and its AutoStar #497 still worked properly I decided that the best way to go would be to mount the ETX OTA on the LXD55.
Another consideration in the decision was that my 17 year old Meade ETX-125AT could experience a similar failure. Being able to mount its OTA on the LXD55 would give additional life to the ETX-125 telescope.
With these points in mind I decided that mounting rings for the ETX telescopes would satisfy my requirements.
I measured both telescope OTAs:
ETX-105 = 125mm diameter, 175mm length for ring spacing
ETX-125 = 147mm, 195mm length for ring spacing
The ADM dovetail plate and rings arrived in simple packaging:
The ADM 11" Universal Dovetail Plate fit precisely on the LXD55 GEM head. Using the supplied pieces, the rings can be attached in one of two ways on the dovetail. They can be attached directly to the dovetail using the supplied bolts (you will have to supply the hex key). Or the rings can be attached to an adapter which can be slid along the dovetail for precise positioning. However, in the orientation of the dovetail for the LXD55 the sliding adapters could not be used. The ADM 175mm rings can hold OTAs 120-160mm in diameter. Here is the ETX-105 OTA mounted in the rings that are directly attached to the dovetail plate:
The ring bolts are just barely long enough to securely hold the 125mm diameter ETX-105 telescope OTA. Of course, the large rings look way too large for the small diameter ETX-105, but since they will do double duty by holding the ETX-125 as well I am OK with that.
The LNT/Smartfinder module on the ETX-105PE used power from the ETX mount and so was removed when I deforked the telescope. Since I needed a finderscope on the ETX-105 I got out an old Rigel Systems QuikFinder that I received in 1999. When I replaced the original CR2032 battery with a new one, the QuikFinder worked perfectly. It was mounted on the ETX-105 using the supplied adhesive strips:
The ETX OTA is heavy enough to require the use of the counterweight on the LXD55. A photo of the complete LXD55 + ETX-105 outside of the observatory appears at the top of this page. Here is a close-up showing the ETX-105 on the LXD55 GEM head:
I have not yet deforked the ETX-125AT from its mount but did check the rings on the ETX-125 OTA. I tested with one ring on the OTA and it fit OK:
There is adequate ring spacing for the ETX-105 OTA and the ETX-125 OTA with the 11" dovetail plate.
Moving the entire assembled mount and telescope is quite a load, even the short distance from the house to the observatory. Removing the ETX OTA, rings, and dovetail as a unit lightens the load considerably, as does removing the counterweight, but requires more trips. I plan to vary how I move it to/from the observatory to determine which is the most comfortable for me.
Using the ETX-105 mounted on the LXD55 GEM worked, but it did have some things I had to work through. First, as is typical with a GEM-mounted telescope, there was the matter of getting used to the eyepiece and finderscope changing orientation as the telescope was slewed from one side of the mount to the other. When I was using the Alt/Az fork mount of the ETX-105PE, orientation was not really a consideration during use. Second, with the ETX in some orientations, the height of the telescope was something that I needed to address. With the LXD55 legs at their lowest extension, viewing through the QuikFinder 1X finderscope when pointed near the zenith was basically impossible. For some objects, the ETX eyepiece would be pointed downwards, and so the low height made viewing difficult. Extending the tripod legs about halfway helped, but it was still difficult to use the QuikFinder when viewing near the zenith. I ended up using nearly the full extension of the tripod legs in order to use the QuikFinder no matter where the telescope was pointing. Of course, that raised the eyepieces quite a lot and required standing to view some objects. Yes, I could have rotated the OTA in the rings, but that would have meant realigning the telescope to the mount axes and would have only eliminated the eyepiece pointed downward. I chose to not do that. The ETX has two eyepiece ports; one on top and the other at the rear. I can use either port as necessary to make viewing more convenient. Since I plan to use the Revolution Imager when using the ETX/LXD55 at star parties, viewing objects won't be a problem.
The ADM dovetail plate and mounting rings met my expectations and have given additional life to my old ETX telescopes. I can now look forward to many more years of observing using the excellent optics of the Meade ETX telescopes even if their mounts go bad. And should the LXD55 ever fail, I can get a new GEM and continue to use the ETX telescopes. The ADM dovetail and rings have been an excellent choice for me.
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Copyright ©2016 Michael L. Weasner / firstname.lastname@example.org
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