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ETX60/70 as a finder scope?

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#1 Jerry-rigged

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Posted 14 August 2012 - 09:10 AM

Howdy gang-

Let me start by saying I like to "think outside the box", but I know sometimes I just end up making things more complicated. So if this sounds too far out in left field, let me know.

I am looking for a finder scope for my 10" dob. I have a Telrad, but I would like something to go with it that give a little bit of light gathering and magnification to help cut thru the sky glow for star hopping. The basic, no base, straight thru 7x50 GSO finder is about $45, and the GSO RACI 8x50 with base is about $80.

But then I start thinking about "other options", small scopes that I could use as a finder scope, but also have the option to use as a stand alone scope, a "grab and go" for quick trips outside... The first two or three options I though of would have set me back $300-$500 (options like the Astro Tech 72mm F6 refractor, almost $400 for the OTA) Then I noticed that ETX60/70's on ebay are often going for $75-$100, sometimes with a few eyepieces or a tripod. If my math is right, one of these scopes with a basic 25mm eyepiece (that I already have) would give me about 14x, and almost 4deg TFOV. A cheap wide field 25mm would give between 4.25 - 4.8 TFOV. (the 7x50 GSO gives about 5 deg, TFOV, I think. Also, the AT72 could get to 5.6 TFOV with a 2" 35mm, 68 def FOV eyepiece, but would cost over $500 for the scope + diagonal + eyepiece)

So with the ETX60/70 - how do they unmount from the forks? My ETX90 has 4 screws, two on each fork. I can de-fork or re-install the OTA in about 5 minutes. Are the smaller ETX's the same? Also, my EXT90 has a "foot" on the bottom of the OTA that mounts directly to a photo tripod - do the smaller ETX's have this?

Last - how is the ETX60/70 as a stand-alone scope? Some places I read it has a built-in barlow? How well does that work? If you push it up to 100x-150x, how well does the image hold up? How would the ETX70 compare to the above mentioned AT72?

Any other thought on these scopes, or using the OTA from one as a finder?

#2 *skyguy*

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Posted 14 August 2012 - 03:13 PM

Why not just "bolt" the entire telescope assembly ... scope, fork arms and drive base ... directly onto a flat area on the dob. The Coulter dobs are so heavy and the ETX 60/70 so light ... a little extra weight shouldn't make a difference! It would certainly save you the additional cost of buying finder brackets.

#3 Stew57

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Posted 14 August 2012 - 04:00 PM

Deforking the ETX 60,70,80 is not a 5 min job but not difficult. I wouldn't want to have to put it back together for a quick vies as the time defeats the grab and go purpose. I think the ETX 80 is the one with the builin barlow. You would need rings to mount the smaller ETXs.

#4 Jerry-rigged

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Posted 14 August 2012 - 05:13 PM

Mounting, I am not worried. If it has the foot for a camera tripod, Like my ETX90, then it will be easy. If no foot, it will be toughter, but still do-able.

How do you De-fork the smaller ETX's?

#5 Jerry-rigged

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Posted 14 August 2012 - 05:18 PM

Google is my friend today...
http://www.cloudynig...28/Main/2010728

Yeah, that is not good for what I want to do with it... :(

Oh well... I guess I could still use it for a finder, but it would be a one way trip. Maybe I can find a cheap one on ebay with a dead mount.

#6 nytecam

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Posted 21 August 2012 - 03:27 PM

I've used a spare ETX-70 deforked and mounted on 'rings' on my 12" SCT for some years - currently an excellent e-finder and autoguider via a tiny SX Lodestar cam :grin:

#7 burb scope

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Posted 22 August 2012 - 12:54 PM

I bought a used ETX-70 OTA from someone who de-forked it from a trashed mount. I bought used 100mm tube rings, mounted them onto a piece of wood, then mounted it all to the top of my NexStar 6SE. Cost me $100 total.
I now having an ETX-70 with working goto. (ha ha!)
I keep a wide-field eyepiece in one port, and a 12mm illuminated reticle eyepiece in the other. Anything that lands in the square of the illuminated reticle is in the middle of a high power eyepiece of the main instrument.
The versatility of a flip-mirror on the ETX outweighs other conventional finders in my opinion.
As an added bonus, the Sun (and Moon) almost fill the entire field of view of the ETX-70 with a Meade LPI camera. This is great for full-disk solar & lunar images, and did a nice job on the recent Venus transit.
By the way, the above poster nytecam takes better astrophotos through his ETX-70 than I ever will with any larger scope!

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#8 Jerry-rigged

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Posted 24 August 2012 - 12:03 PM

Thanks, glad to hear I am not crazy... :)

NYTECAM: nice site! I see you have torn your etx down to nuts and bolts... I was wondering - I have seen a few 60/70's on Ebay with loose mirrors or broke focusers sell for less than shipping. How hard would it be to fix these? Is the mirror a glue down affair? Is the focuser screw a standard thread size?

#9 nytecam

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Posted 10 September 2012 - 04:44 PM

NYTECAM: nice site! I see you have torn your etx down to nuts and bolts... I was wondering - I have seen a few 60/70's on Ebay with loose mirrors or broke focusers sell for less than shipping. How hard would it be to fix these? Is the mirror a glue down affair? Is the focuser screw a standard thread size? [/quote]Bit hit 'n' miss I suspect but if its low cost what's there to loose :question:

#10 Jerry-rigged

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Posted 12 December 2012 - 12:01 PM

Follow up- Well, I done and did it. Payday lined up with a EXT80 "for parts or repair" on ebay, and I won it, $62 shipped. Supposedly the OTA is fine, but the ALT motion is broke, not sure if mechanical, drivetrain, or something else. My plans are to de-fork the OTA and scrap the base, so if anyone here wants some parts, let me know. I will check out all out and see if the issue is repairable before I trash anything...
Once the scope gets here I will probably start a new thread. Or not. :)






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