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Mount Ratings and Counter Wieghts

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#1 Doug N

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Posted 13 March 2009 - 08:27 AM

I have been looking for a new scope and have a question of the weight capacity of mounts. Specifically I was looking at the Orion EQ-G Mount which is rated an 40 lbs. For a mere :) $2000 you can get this mount and a 10" Newtonian. Given that I would add some more equipment, such as a guide scope, I was looking at the total weight as to not exceed the 40 lbs. I was fine until I wondered about the counter weights. Looking at the data the OTA is 27 lbs. It also uses two 11 lbs counter weights. Total of 49 lbs. It would seem that the mount is over matched. However, I don't see any discussion about any problems.

My conclusion is that the capacity rating of the mount does not include the counter weights. The evidence supporting this would be the fact that the mount itself is advertised with the counter weights. The question is how to interpret the capacity of a mount. It would seem in this situation that you don't have to include the counter weights against the capacity. Is this true?

This also brings up another question. There would be two mechanisms that would determine the capacity of a mount. These are the total weight where the mount would cease to function properly, and the inability of the mount to provide proper counter balance. Which mechanism asserts itself first? An interesting note from the field is that there are many complaints about the LX75 SN-10 mount being over matched. There are however those that say "if properly balanced ...". This would give credence to the 'inability to counter balance' mechanism.

The engineer in me wants to know ... :).

#2 Lane

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Posted 13 March 2009 - 08:46 AM

The weight capacity doesn't include the counterweight. It also does not take into account long OTA's. However the only reason any of this matters is if you are concerned with vibration damping time. There are plenty of people using the EQ-G on this site with over 65 lbs of equipment on top of it and are very happy with that. I am certain that it needs to be very well balanced for this to work. Obviously if they touch that scope it will vibrate for 20 seconds but that is not a problem if the scope it not in the path of the wind and you use an electric focuser. For visual use without an electric focuser and outside where the wind is a concern, this amount of weight would simply not work. In fact, I would keep the load at or below 30 lbs and definitely use vibration suppression pads. Otherwise you will be dealing with vibration damping times that you may find unacceptable.

#3 mclewis1

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Posted 13 March 2009 - 12:14 PM

The weight capacity doesn't include the counterweight.


Usually, but watch out for some older Vixen specs, in some cases they used to include the counterweights in the mount's capacity rating. That made for some very confusing spec matching exercises.

There are so many variables in this exercise of matching mounts to OTAs that you can spend eons researching the possibilities.

As Lane said longer tubes reduce the carrying capacity somewhat, anti vibration pads improve it. The quality of the tripod, how nice and snug all the bolts are (overall condition of the mount if used), the length and type of saddle on the mount, how smooth the gears are, how well balanced your scope(s) are, what type of work (imaging vs. visual), what focal length scope(s), portability requirements, budget, HC software, PC control capability, autoguiding capability, etc. etc.

Or if you want to simplify it, find out what others are doing with setups similar to your needs and try and avoid being at the manufactures spec limit, that way you're buying some extra headroom which should make up for some of the variables mentioned above.

#4 Trebor777

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Posted 13 March 2009 - 02:20 PM

The weight capacity doesn't include the counterweight. It also does not take into account long OTA's. However the only reason any of this matters is if you are concerned with vibration damping time. There are plenty of people using the EQ-G on this site with over 65 lbs of equipment on top of it and are very happy with that. I am certain that it needs to be very well balanced for this to work. Obviously if they touch that scope it will vibrate for 20 seconds but that is not a problem if the scope it not in the path of the wind and you use an electric focuser. For visual use without an electric focuser and outside where the wind is a concern, this amount of weight would simply not work. In fact, I would keep the load at or below 30 lbs and definitely use vibration suppression pads. Otherwise you will be dealing with vibration damping times that you may find unacceptable.


I put close to 50lbs on my Atlas. I use vibration suppression pads, but the "20 seconds of vibration" is way overstated IMO. Visually, if I knock the tripod or OTA, or a guest of wind comes, vibration only last for a couple of seconds. I'm not putting 65 lbs on there, so I can't comment on vibration times with that weight. But around 50 lbs the vibrations are minimal. But if only put my 7lb AT80EDT on there vibration is basically non-existant.

But the Atlas can handle more then the 40lbs it's rated for. Like with ANY mount, the more weight you put on there, the more balance is an issue and the more vibration is an issue.

#5 GJJim

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Posted 13 March 2009 - 02:41 PM

One reason for rating a mount as load+counterweights is that is the maximum load capabilities of the bearings. The axis bearings have to handle the full dead weight even if the load is perfectly balanced.

Another issue is inertia of the load. People often find out the hard way that moving a high inertia load such as a long refractor is more stressful on drive gears and motors and generally requires a bigger mount than a compact SCT, even though both have the same weight.

#6 Lane

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Posted 13 March 2009 - 02:56 PM

"vibration only last for a couple of seconds"

Look in a mirror I think your nose has just gotten several inches longer :roflmao:

#7 Trebor777

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Posted 13 March 2009 - 03:17 PM

"vibration only last for a couple of seconds"

Look in a mirror I think your nose has just gotten several inches longer :roflmao:


Have you looked through my set-up? Didn't think so.

I have close to 50 lbs on my Atlas and have not had any issues with 20 seconds of vibration. Like I said, I've had maybe 5-7 seconds of vibration after a big gust of wind or I accidentally hit the tripod or OTA.

And I don't like being called a liar. What's that quote from Full Metal Jacket about people from Texas?

Anyone who has 20 seconds of vibration doesn't know how to set up and balance a mount correctly or simply can't count and thinks a quarter past 5 means 5:25.

#8 Lane

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Posted 13 March 2009 - 03:27 PM

Sorry if you were offended.

But I never said you had 20 seconds of vibration and you never said you had 5-7 seconds of vibration. You said you had a couple of seconds of vibration.

Couple = 2

So my comment was only to point out that there Ain't-No-Way you could possibly have 2 seconds of vibration with all that weight. I would have guessed closer to 10 seconds. But 5-7 is bad enough. To me anything over about 2.5 is simply not acceptable for visual use, way to frustrating for me.

#9 Skylook123

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Posted 13 March 2009 - 03:58 PM

"vibration only last for a couple of seconds"

Look in a mirror I think your nose has just gotten several inches longer :roflmao:


I run over 40 pounds on my 10" f/10 SCT/Atlas, and without pads on concrete or asphalt it runs about seven seconds to calm down. With Celestron pads or on grass, about three at most. I'm constantly whacking something so I have a large sample size.

#10 Lane

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Posted 13 March 2009 - 04:22 PM

3 seconds? Jim am I going to have to offend you too :lol: I think I already reached my quota for the day :o

Now Jim - If you pop in an eyepiece and run it up to say about 250x aiming at some little stars and you thump the side of that telescope and start a stopwatch at the same time. Then you peep into that eyepiece and wait for every last vibration to go away and then stop that stopwatch, it reads 3 seconds :question:
Because if you can honestly say you did something like that then that would be objective data that could not be ridiculed by skeptics like me :grin:

#11 Trebor777

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Posted 13 March 2009 - 04:32 PM

3 seconds? Jim am I going to have to offend you too :lol: I think I already reached my quota for the day :o

Now Jim - If you pop in an eyepiece and run it up to say about 250x aiming at some little stars and you thump the side of that telescope and start a stopwatch at the same time. Then you peep into that eyepiece and wait for every last vibration to go away and then stop that stopwatch, it reads 3 seconds :question:
Because if you can honestly say you did something like that then that would be objective data that could not be ridiculed by skeptics like me :grin:


I'm going out tonight. I'll bring my stop watch I use for coaching basketball. There's no need to argue about vibration time, but it would be an interesting report. I'll take some notes tonight. I also have to report on my MPCC in my SN10. I'll be busy tonight.

#12 Lane

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Posted 13 March 2009 - 05:08 PM

Actually I think it is worth arguing about. Because for some of us it is very important. If a scope has to much vibration then you cannot focus it easily at high power and in general it isn't as much fun to use. In fact, this is the very reason I joined this site. I was trying to buy a new mount at the time and hoped to make sure of the damping time before I got it. Needless to say I got terrible advice out here on CN, it was in fact Mike at OPT that determined the actual damping time of the scopes I planned to buy. He was absolutely correct too, every single person on this site that gave me advice was completely wrong. So I am on a little personal campain to stamp out misinformation on this site, not necessarily for myself, but for the next poor guy that wonders out here seeking advice. And I don't believe anyone out here is deliberately lying either, I just think people basically tend to give subjective answers to questions that really need be answered objectively.

#13 Trebor777

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Posted 13 March 2009 - 05:57 PM

Actually I think it is worth arguing about. Because for some of us it is very important. If a scope has to much vibration then you cannot focus it easily at high power and in general it isn't as much fun to use. In fact, this is the very reason I joined this site. I was trying to buy a new mount at the time and hoped to make sure of the damping time before I got it. Needless to say I got terrible advice out here on CN, it was in fact Mike at OPT that determined the actual damping time of the scopes I planned to buy. He was absolutely correct too, every single person on this site that gave me advice was completely wrong. So I am on a little personal campain to stamp out misinformation on this site, not necessarily for myself, but for the next poor guy that wonders out here seeking advice. And I don't believe anyone out here is deliberately lying either, I just think people basically tend to give subjective answers to questions that really need be answered objectively.


I thought I was impatient. :shocked:

Anyhow, I mount a huge SN10 on my Atlas and vibration is rarely an issue. The SN10 w/ my dew shield is 4' 2" long.
Like I said, only when a big gust of wind comes or I knock into it.

Also note, I have a dual Losmandy/Vixen Saddle, a Losmandy dovetail on the SN10 and a thicker longer CW shaft (18"x1"), a Moonlite focuser and I replaced all the bearings and relubed everything. With my set-up, vibration isn't an issue to me, weather conditions are. I don't have vibration issues when I focus either. That's all I'm trying to get across. I don't want people who are thinking about buying an Atlas to think is shakes like crazy (20 seconds), that's simply not true.

And this is coming from someone who had a Celestron 130SLT which would vibrate by just looking at it.

I'm sorry you got wrong information on here. I've never had someone give me blantely incorrect advice - well someone from my astronomy club did once, but that's a different issue.

#14 Trebor777

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Posted 14 March 2009 - 12:40 AM

My vibration test: Actually, a lot better then I originally thought.

Fully loaded Atlas EQ-G. SN10 & AT80EDT - Mount legs were not extended, but placed on vibration suppression pads. I was on grass.

49lbs of equipment + 45lbs of counterweights. The SN10 with dew shield is 52" long.

Used a 5mm TMB Planetary in my SN10 that's 203x. No wind at all tonight. I used a stop watch to time.

I viewed Saturn, tapped OTA, usually it would stop vibrating within 3 seconds. Mostly in the 2.25sec to 2.85sec range. The longest time was 3.71 seconds. I also did it with a 9mm and my 23mm Ax, same thing, within 3 seconds vibrations would stop, somtimes a little over 3 seconds, but not once did I reach 4 seconds.

I did the same thing in the piggy-backed AT80EDT F/7 560mm. With a 4mm TMB 140x (&9mm and 23mm Ax) Vibration time was a little longer. Mostly in the 2.70sec to 3.30sec range. Still nothing over 4 seconds.

Of course wind would act differently on it but once the wind stopped, the vibrations would stop within 3-4 seconds. Vibration isn't the problem, weather is.

#15 Trebor777

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Posted 14 March 2009 - 01:04 PM

"vibration only last for a couple of seconds"

Look in a mirror I think your nose has just gotten several inches longer :roflmao:


I run over 40 pounds on my 10" f/10 SCT/Atlas, and without pads on concrete or asphalt it runs about seven seconds to calm down. With Celestron pads or on grass, about three at most. I'm constantly whacking something so I have a large sample size.


3 seconds on grass w/ vibration pads is basically exactly what I got. Usually quicker than 3 seconds though.

#16 Doug N

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Posted 14 March 2009 - 02:46 PM

Thanks for the data. It will help.

Doug N.

#17 John Miele

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Posted 14 March 2009 - 03:38 PM

For what it's worth, here is some vibration test data I posted a while back with my Atlas mount and a C11.

http://tinyurl.com/bwts6w

#18 Lane

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Posted 15 March 2009 - 06:19 PM

This is very interesting information. I would have never have believed overloading an atlas mount that much could actually stabilize the mount. Must be the inertia factor. Still over the damping time I consider acceptable but I guess a lot of people would be ok with it. I posed this same kind of question about the CGE 1400 a while back and the most common response from owners was that it had between 3 and 4 seocnds of damping time with the vibration pads in use. That mount is rated at 65lbs and the 14" is only a little over 45 lbs when it is loaded up with diagonal, eyepiece, and finder. This might explain why Celestron was considering eliminating the CGE. Maybe the CGEM was really intended as a replacement. I wonder if the guys at OPT would be willing to drop a 14" celestron on a CGEM mount and test out the damping time. It could be better than the CGE.

I also read John's information from the other post, I had a feeling that adding the mount extension would cut damping time even more and his results support that assumption. I got one on order now. I am also considering lining the inside of it with one of the anti-vibration pads that they sell at the audio stores for stopping vibrations in cars.

This has me very excited, I may go ahead and get a dual mount bar for my CGEM so I can have my C11 and the ED80 on board at the same time. Having the wide view and the narrow view at the same time would be great.

Thanks for all the info.






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