Adapting to the Big Picture
The 1.25” 26mm eyepiece that came with this scope provides a 0.82 degree field of view (FOV) at 73x. In order to get a bigger, better view, I purchased a 40mm Plossl that modestly broadened the FOV to 0.92, but reduced the magnification to 48x.
This was somewhat of an improvement, but I still wasn’t completely satisfied, so an ad I saw recently in Astromart really caught my attention. It was placed by CNC Supply, Inc. and read as follows:
“This 2" ETX eyepiece adapter can really open up your view. The results are remarkable. Works well even with wide field 40mm eyepieces. Anodized aluminum construction with a brass compression ring to prevent marring eyepiece barrels. Threaded for 1.25" eyepiece filters.
“Important Note: This adapter requires a fair amount of back focus and is only recommended for catadioptric telescopes with a moving mirror focus system, will not work with most reflectors or refractor. Not for ETX60/70/80 due to lack of back focus.”
This sounded intriguing. With this adaptor in my ETX, I could use my 2” ultra wide angle eyepieces in order to increase the field of view by as much as 50% or even more in some cases without reducing the magnification.
The $49 price tag seemed a bit steep for this little item, so I thought I’d check out AgenaAstro.com. I’ve done business in the past with Manish at Agena and found him to be nothing short of a class act. His prices always seem to be competitive, so I was not surprised to find what appeared to be a similar adapter for $20 shipped to my door.
For 20 bucks, it might be worth a try, but before I placed my order, I checked out Mike Weasner’s ETX website—www.Weasner.com/etx. Mike’s site has an abundance of information related to the ETX, but didn’t have any reviews on this adapter. Mike did tell me, though, that he would be concerned about vignetting and balance problems.
Vignetting was one of my concerns as well, but I had already tried hand-holding a couple 2" ultra wide angle eyepiece's--very nice, sharp, wide angle views right to the edge. In fact, my 26mm Orion Q70 has a slightly wider FOV than my 1.25” Meade 40mm eyepiece.
Though Mike’s website did not have any reviews on an adapter of this sort, it did have an article by Chris Brown dated December 17, 2005. Chris attached a 1.25” barrel to an inexpensive 2” Erfle and was pleased with the results when used in his ETX-90. “Achieving focus was not a problem, nor was the weight of the eyepiece, due to its lightweight construction.” My larger ETX-125 then should be able to handle a somewhat heavier eyepiece even with the added weight of the adapter.
I cautiously tested the eyepieces but was not terribly concerned about weight since my 1.25” 6.7mm Meade UWA eyepiece weighs about the same as my 2” 26mm Orion Q70. I’ve never had any problem with the weight of my 6.7mm UWA, however the heaviest 2” eyepiece I have is about 7 oz more.
So far, I’ve tried the following 2” eyepieces:
1. 30mm Wollensak -- weight: 19.2 oz; length: 114mm
2. 32mm Orion Q70 -- weight: 14.4 oz (+/-); length: 120 mm (+/-)
3. 26mm Orion Q70 – weight: 11.9 oz (+/-); length: 103mm (+/-)
4. 15mm Knight Owl -- weight: 9.2 oz; length: 80mm
My results were as follows:
Vignetting: No vignetting with any of these eyepieces. Just a nice sharp edge.
Focusing: No problems at all.
Balance: This scope is nose heavy anyway, so even the heaviest of these eyepieces could only help to balance the scope.
It should be noted that I did not do any extensive testing with the scope in the Equatorial/Polar mode. I did briefly put the scope in Equatorial/Polar mode (about 42 degrees) with the heaviest eyepiece to see what would happen. I can’t imagine that there would be much risk of even the heaviest eyepiece toppling things.
Slewing: I realize it’s not very scientific, but I’m just basing my conclusions here on sight and sound. When I slewed the scope at various speeds, I did not notice any hesitation nor did the motors sound as if they were straining at all.
I think I may have to qualify this though. Let’s be honest, these drives are not quiet to begin with. In fact they sound very much like dueling coffee grinders and didn’t sound any better or worse with even the heaviest eyepiece.
If you’re concerned about auto-slewing with a long, heavy eyepiece sticking out of the scope, you can always remove the eyepiece and then replace it when the slewing stops.
You definitely need to be a bit more careful when aiming at or near the zenith, but there still seems to be plenty of clearance.
Fit: I was surprised to see that the adapter seems very stable even with the longest, heaviest eyepiece—nice snug fit without any wobble.
Leverage: I would be careful at star parties. Sometimes people want to hang onto the eyepiece as if it were a handlebar. With the additional length/leverage of a 2” eyepiece plus adapter, there could be a problem here.
Conclusion: Overall, I’m very please—thrilled in fact. For 20 bucks, I’m able to significantly broaden the view through my ETX 125. Without this adapter, I would never even dream of turning my scope to the double cluster (NGC 869 and NGC 884) and expect to see both in the same field—one or the other, but not both. With this nifty little adapter and an ultra-wide-angle eyepiece, the pair just fit neatly within the field of view. I’m now enjoying a much bigger picture of the universe.
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