Author Topic: For the last time: GM-8 15lbs vs 30lbs  (Read 3180 times)

Tyler Fonseca

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For the last time: GM-8 15lbs vs 30lbs
« on: December 28, 2017, 11:32:41 AM »
Can anyone SHOW ME the difference in tracking quality between a Losmany GM-8 loaded to 15 pounds and the same one loaded to 30 pounds? I guess some tracking plot? I don't know how to do that stuff yet, and I don't think I can even come up with the 30 pounds of equipment. Plus, I just have the stock worms and blocks.

I'm going through a Cat Crisis. I can't seem to buy an old Celestron 8 with out feeling sorry for it and getting it an old fork/wedge/tripod to put it on, instead of just slapping a bar on it and putting it on my GM-8! I'm even going to end up with an extra fork after this weekend.

My *only* recourse is to just buy a new Edge scope that was never attached to a fork. What I'm trying to figure out is if my GM-8 can handle the 9.25" scope (20 pounds) with all the extra parts for photography which will for sure bring it up into the 30 pound area. If it really can't handle it then I'll go with the 8" (13 pounds). I'm not going for National Geographic quality pictures or anything, but if 30 pounds is REALLY going to be a lot worse then I'll stick to the 8" like the mount was made for.

Are there plots on the web somewhere?

I really need to see a shrink.

Thanks!

Bob



Lance Soto

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Re: For the last time: GM-8 15lbs vs 30lbs
« Reply #1 on: January 12, 2018, 03:08:07 AM »
It's not just the 30 lbs, it's the long focal length of the scope. I don't have a GM8 or any graphs to show you, but I'd be willing to bet you'd be very under-mounted with the GM8. You would be very sensitive to even the slightest wind, and you'd have to get everything totally right to even have a chance.

Much safer to go with the Edge8 and get a reducer. There's going to be little advantage to a 9.25" vs. an 8" for AP. Even for visual (there I've had both scopes) the 9.25" is only (marginally) superior to the 8" when you're at a dark site, or if you have great optics and are in a great seeing location. And if it's a question between a regular 9.25" and an Edge8, I'd take the Edge 8 any time for AP *or* visual. Mine is super-sharp.

Devon Dank

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Re: For the last time: GM-8 15lbs vs 30lbs
« Reply #2 on: January 12, 2018, 05:40:39 PM »
That's what I'm wondering. Everyone says more weight is worse (and, yup, you're right, more mm's too), but I'd just like to know how much -- however it can be quantified. I can't imagine I won't get a bigger mount someday, but no time soon where the 9.25 will be fine. Will the 9.25" just be a royal mess to deal with until then...or maybe will it not really be that bad. I'm looking for some kind of numbers.

Otherwise, yeah, I agree with you. There was a big thread a while back about 8 Edge vs 9 regular. I think I would go Edge either way. And with the 8 the extra $1000 won't be under appreciated, either.

Thanks!

ermaudyvi

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Re: For the last time: GM-8 15lbs vs 30lbs
« Reply #3 on: January 13, 2018, 02:51:17 AM »
Thinking more about this...

If I have a C8 on the mount and it comes out to 15 pounds, then I throw a 15 pound bag of sand on top and rebalance the mount does it become twice as unstable? Four times? Only half again? Or does a weight change like that even matter much? I don't know what the units of instability are.

wagishohots

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Re: For the last time: GM-8 15lbs vs 30lbs
« Reply #4 on: January 22, 2018, 09:12:30 PM »
There's only one number in the table for the GM-8.  I see what you mean. Tricky.

Maybe I'd better not push things. The "8" was made for an "8", so...and if I ever end up getting what I've wanted all my life -- a C14 -- I'll be able to use the C8 as a finder. The C9 would be kinda big and funny looking.

Thanks!

ecapwaiwa

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Re: For the last time: GM-8 15lbs vs 30lbs
« Reply #5 on: January 25, 2018, 01:19:57 PM »
I guess that means getting the C8 is the right decision.
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Cleo Wickware

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Re: For the last time: GM-8 15lbs vs 30lbs
« Reply #6 on: January 28, 2018, 10:48:29 PM »
Quote
It's not just the 30 lbs, it's the long focal length of the scope. I don't have a GM8 or any graphs to show you, but I'd be willing to bet you'd be very under-mounted with the GM8. You would be very sensitive to even the slightest wind, and you'd have to get everything totally right to even have a chance.

Much safer to go with the Edge8 and get a reducer.

Hi Bob - I think Stelios is delivering some sage advice. I have an Edge 8, GM 8 and will give it shot without the reducer just for the sheer fun of trying it. Back in 2005 when I didn't know any better, I loaded up the GM8 with 28 pounds, legs fully extendedwith counterweights(21 + 7 ) high as they could go.I had a tent which helped. The mount had a polar alignment scope which I think was the make or break difference. This was at a star party.
About a hour's worth of nervous balancing.
At that time (just like today) I'm happy getting anything on the chip. That night I was doing 120 seconds 45 exposures throwing out six. For a cluster I had read you could get away with less time. There wasn't a great deal of correcting from the guider as I recall.
It's not great but the stars aren't eggs, so it can be done but as Stelios suggests a lot of good things have to happen to have a chance.

Good luck with your Edge decision I love mine.

David






Michael Ritchie

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Re: For the last time: GM-8 15lbs vs 30lbs
« Reply #7 on: January 31, 2018, 08:39:18 AM »
I have owned a GM-8 for years. after a while you get a "feel" for how it will behave. I "feel" like the C8 is going to be the right size Edge for that mount. The C9.25 not so much... especially after the cameras and guiding gear.

FWIW.

haigeoredis

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Re: For the last time: GM-8 15lbs vs 30lbs
« Reply #8 on: February 03, 2018, 02:44:25 AM »
There is no online database of scope/mount/setups tracking logs.
Take a look at my Rig #1 and Rig #2 side by side.
Doesn't the C-9.25 system look visually balanced with the MX+ beneath?
Doesn't the 80mm system look visually balanced with the GM-8?

C-9.25 on the GM-8? Only visual.