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Convert an EXT 70 into a finder scope for my DOB

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#1 lfinn

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Posted 11 August 2013 - 05:13 PM

Hi,

I have an EXT 70 which I don't use and seeing as i'm more of a deep sky observer i doubt I will ever use it. I have been thinking of mounting it on my big Dob as a finder.
Do you think it would make a good finder for deep sky objects and if yes what recommendations on mounting rings would you have to do so?

Thanks in advance for your advice

#2 jgraham

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Posted 11 August 2013 - 06:53 PM

Why sure, the ETX-70 should make a great finder. I use an ETX-60 as a guide scope on my de-forked 10" LX6. I'm not sure where the rings came from as they were on the LX6 when I bought it. (I moved the rings from the OTA to the dovetail to improve the balance.

This shows my present setup.

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#3 jgraham

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Posted 11 August 2013 - 06:58 PM

Here's a thought as a possible Plan-B. Instead of remounting your ETX-70 as a finder, add a laser pointer to it and use it as a point-to system for your Dob. I did this with my Lightbridge 16 and it works great! I originally took a bunch of spare parts including a #884 field tripod, a DS-2000 mount, a 2045s 4" SCT spotting scope, and a laser pointer to make my first point-to system. The idea is to align the laser pointer with the ETX, use the ETX to point to a deep sky object (if you can't see it in the ETX just synch it on a nearby star, it'll be close enough when you GoTo the object), then follow the laser out to the end with your Dob. I recently built a second point-to system using an ETX-105, and it works great!

This is my original point-to system set up with my Lightbridge 16. I set the point-to scope just north of my Dob so it doesn't get in the way.

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#4 jgraham

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Posted 11 August 2013 - 07:00 PM

My ETX-105 set up as a point-to system. I just replaced the original finder with green laser pointer. The laser looks really neat through the scope. :)

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#5 lfinn

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Posted 11 August 2013 - 07:52 PM

I like both ideas but the tracking on ext 70 is garbage. Thats why i stopped using it in the first place. If you have recommendation on the size of rings needed or any inexpensive rings and mounts would be ideal.

My DOB is a strut style and i have wooden brackets that mount on the strut so i can mount the dovetail or something like that.

Any ideas?

#6 jgraham

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Posted 12 August 2013 - 11:42 AM

Astronomics has some nice finder ring sets (they have an 80mm set on sale right now). I'd suspect that the usual suppliers (OPT, Orion, etc.) do as well. As for the size, I'm not sure which end of the ETX-70 is smaller. You may want to cut some circles out of cardboard and see how small of an opening you can slip the telescope through.

#7 David Castillo

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Posted 29 August 2013 - 03:21 PM

I have thought of this same conversion on my scope, but I don't know if there will be a balance issue on my fat-a$$ 16" LB. It already weighs a ton and I don't want to de-fork it to find that it could be an anchor mounted to the OTA. Does anyone have any idea how much this weighs?
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#8 jgraham

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Posted 30 August 2013 - 08:20 PM

Not much. I'd be tempted to mount it on the lower tube assembly instead of the upper. On my Lightbridge 16 and my homebuilt 16.5" I've worked hard to keep the upper tube assembly light and simple. Opitical finders on the lower assembly, laser pointers on the upper.






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