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How hefty a mount for 10" RC

Started by agJohn, 06/13/2013 07:55PM
Posted 06/13/2013 07:55PM | Edited 06/13/2013 10:05PM Opening Post
I'm building a 10" Ritchey-Chretien scope (using wonderful Star Instruments optics) that I have almost got ready to put on a mount. What I'm wondering is, how reliable are the manufacturer's ratings of what a mount's load-capacity is? And are those values likely to be substantially different in terms of reliability from one manufacturer to another? Is there a minimum price-range I should be looking at?

OTA specs:
Weight w/o eyepiece ~20 lbs.
Tube is 12.4" diameter and 30" long
(not counting the eyepiece holder--so with a decent eyepiece, it'll be between 36 & 40" sky-end to exit-pupil).

I don't want to get something that will be jiggly (been there, done that), but I also don't want to get something that will be a real pain to move around (so I'm hoping to keep the weight of the mount/tripod low enough that I won't not use it because it's a beast to move around). I do not anticipate doing long exposure astrophotography or even spending the money to get the gear to do it. I'm mostly interesting in viewing and would like to get back into school outreach (which I enjoyed doing some of in my younger days).

As a concrete example, I've looked at the iOptron iEQ30 which is supposedly rated at 31 lbs capacity. Assuming there's a decent finder and perhaps (if I ever tried it) a piggy-back camera or moderate refractor on the thing, it would seem that ~30 lbs would be a reasonable amount of actual weight. So, is that mount really going to be hefty enough or should I be looking at the iEQ45 (rated at 45 lbs)? Another mount I've considered is the Celestron CGEM (which one place lists as having a 40 lb capacity--overkill or about right if the ratings are optimistic?). Interestingly enough the CGEM DX appears to be exactly the same mount on a heftier tripod and the same place says it's rated at 50 lbs. The lower-down-the-price-chain VX says it will take 30 lbs, but a review I found suggested that was optimistic and you'd be better off w/ half that.

So, suggestions, experiences, advice, tales of woe or joy--all most welcome!

Posted 07/04/2013 08:23PM #1
Hello John
That sounds like quite the project that you are undertaking. In terms of what mount capacity that you need, it depends on what you are planning to use your mount and telescope for. If you are planning to use your scope for only visual use, then you can probably go with a mount that is rated at the weight of your equipment (i.e. if your scope weighs 20 lbs, then you can use a mount that is rated up to that capacity). For astrophotography, one has to have more carrying capacity, by a factor of 2 (i.e. if your telescope and equipment weighs 20 lbs, then the minimum mount capacity should be up to 40 lbs). Generally, it is better to have more capacity than you may initially would need. Astrophotography involves a lot of equipment (e.g. cameras, guider & guidescopes, filter wheels, etc.) all of which requires mount capacity. More is better is the general advice in regards to astrophotography. Good luck with your project.
Posted 07/08/2013 03:50AM #2
The biggest concern is the moment arm of your mount. Once you exceed 36 inches you have to start considering the shake and oscillations that might happen from all sorts of factors including wind.

I'm using a G11 with Geminin on a C 9.25 and a ton of stuff hanging off the back for photography. But if I were to have something 2 or 3 times as long there's no way the G11 could handle it.

But the Losmany Titan might work. You might consider buying a used Titan, put a Gemini 2 system on it and upgrading the worm if you need to with an Ovision worm from France.

By the time you get done it will be pretty pricey but when it comes to mounts you only want to do this once. Buying and selling back and forth to get the right thing only wastes money.

And then there's Astrophysics...

Tom P.

Some astronomers see things as they are and say WOW!

Some astronomers see things that were never really there and say it's AVERTED VISION.
Posted 07/24/2013 11:47AM #3

I have a scope that is about the same size as yours, but weighs quite a bit more (that old-school construction, you know). I use a Losmandy G-11 for visual-only observing and it's fine, when it's carefully balanced. However, take seriously those that are cautioning you about moment arms and off-center loads. I'm sure my G-11 would handle a 60 lb scope really well if it were 4 3/4" in diameter and 12" long. However, if I don't balance my actual scope very carefully, then I can hear motors whining (and sometimes stalling) while the scope is moving, and it gets the shakes. Even changing from heavy eye pieces to light eye pieces can cause a motor stall at times.