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Questar 7 and Losmandy GM8 mount

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11 replies to this topic

#1 Mike Allen

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Posted 17 January 2020 - 02:02 PM

Anyone have any experience with mating a Questar 7 with a GM 8 mount, for visual use only?  Max load for this mount is specified at 30-40 lbs.  Both Jim at Questar and Losmandy rep said there is no problem.  An additional question I have would be, what is the amount if counterweight required on the dec axis to balance the 17 lb scope?



#2 Richard O'Neill

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Posted 17 January 2020 - 02:41 PM

One can easily determine the weight required by positioning the Dec shaft horizontally and suspending various weights on a sliding string on the shaft. Easy as pie. flowerred.gif

 

PS. One could also use a fish scale instead of a string and bathroom scale.


Edited by Richard O'Neill, 17 January 2020 - 02:44 PM.


#3 Kaydubbed

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Posted 17 January 2020 - 03:37 PM

Noooo put it in a box and never use it ever! It is too pretty to use!

 

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#4 Mike Allen

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Posted 18 January 2020 - 11:00 AM

One can easily determine the weight required by positioning the Dec shaft horizontally and suspending various weights on a sliding string on the shaft. Easy as pie. flowerred.gif

 

PS. One could also use a fish scale instead of a string and bathroom scale.

I appreciate your advice, and I understand and have used the method you describe.  However, I am looking for information from someone who has already walked down this path.  Information about the dovetail adapter and general description about how well the GM 8 works with the Questar Astro 7 model would be appreciated.  I currently use a 15 lb refractor on this mount with no issues.  The Q 7 Astro weighs 19 lbs with diagonal and finder, so I think the GM 8 would indeed be fine for visual use.



#5 Steve C.

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Posted 18 January 2020 - 11:17 AM

How much does the current counterweight weigh? If it’s at the end of the shaft for a 15 lb. scope, then you obviously need a heavier weight. If it isn’t at the end, then simply moving it down may work. 
 



#6 Mike Allen

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Posted 18 January 2020 - 12:33 PM

For the 4-inch refractor I use one 7 lb counterweight that rests about 2/3 of the way down the shaft, depending on whether I use 1.25 or 2-inch accessories.  The Q7 Astro would sit a little farther out from the mount saddle because of the larger tube, therefore affecting the balance on the RA axis more than just the extra weight would indicate.



#7 HansD

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Posted 19 January 2020 - 04:41 PM

I have personally used a Q7 on a GM-8 and the mount did just fine. I could have used a little more on the counterweight side, like perhaps an 11 lb and 7 lb instead of the two 7s. But it was stable and didn't seem to tax the mount at all. The picture of Jupiter was taken at 400 feet elevation in a 5-10 mph wind.

 

Hans

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#8 Steve C.

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Posted 19 January 2020 - 04:48 PM

Nice setup!



#9 Mike Allen

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Posted 19 January 2020 - 04:57 PM

Beautiful !  A picture is worth a thousand words.  Thank you so much.

 

One additional question.  Can you tell me what size and number if bolts hold the scope to the dovetail plate?



#10 HansD

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Posted 19 January 2020 - 05:01 PM

As I recall it was either 5mm or 1/4" x 20. Also, the attachment of the dovetail plate to the scope is the weak link. There are two threaded holes in-line only a couple inches apart and so I felt like I really had to cinch down on the screws on the dovetail plate to make it tight enough so the scope wouldn't move on the plate. I wouldn't recommend removing and installing it every time you used it so we ended up trimming the foam in the case so the plate could stay in place.

 

Hans


Edited by HansD, 19 January 2020 - 05:03 PM.


#11 Mike Allen

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Posted 19 January 2020 - 06:13 PM

As I recall it was either 5mm or 1/4" x 20. Also, the attachment of the dovetail plate to the scope is the weak link. There are two threaded holes in-line only a couple inches apart and so I felt like I really had to cinch down on the screws on the dovetail plate to make it tight enough so the scope wouldn't move on the plate. I wouldn't recommend removing and installing it every time you used it so we ended up trimming the foam in the case so the plate could stay in place.

 

Hans

Thanks so much again.  You confirmed my guess about the weak attachment point of the dovetail.  That will be the very first item that I will have addressed.  The attachment holes that Questar provides must have changed over the years.



#12 RonLevandoski

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Posted 22 January 2020 - 12:36 AM

I have a friend who just purchased a Q7. He has it mounted on a Losmandy G-11. The tracking is excellent and the mount doesn't seem to even know that the scope is attached. Again, overkill in a good way. 

 

ronlevandoski


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