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Mount / tripod orientation

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#1 cavefrog

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Posted 13 April 2011 - 11:11 AM

I believe I read that some people prefer one of the legs of a tripod should be directly under the counterweight bar as the scope is set and pointed at polaris for stability. this make sense to me especially for heavier / longer scopes.
I have a CG5-ASGT, and was trying to understand how to do this. I have an Orion 16" extension on this setup, but no matter what screw holes I line up on, the counterweight bar will not line up on any one of the legs. It would be the same result without the extension. The only way I can see to accomplish this is to drill new holes.

the questions, is this configuration more stable than stock? If so, why did the company not make it so? Also, am I correct in assuming that new holes have to be drilled in order to do this?

As I typed out this post, I thought about just removing the bottom lineup pin that fits into the extension on the tripod. Duh! I guess that would be the easiest way to do this.

Theo

#2 RTLR 12

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Posted 13 April 2011 - 11:31 AM

Theo,

That's how it's done.

Stan

#3 Asimov

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Posted 13 April 2011 - 11:50 AM

I'm guessing they did it this way at the factory using the theory that 2 legs carry the weight evenly between the 2 thus halving the weight on each leg..Some theories work & some don't.

#4 7331Peg

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Posted 14 April 2011 - 12:40 AM

I just did that on an old manual CG-5 last week - just me and a hack saw. :smash:

I can still loosen the knob on the underside of the head just a bit to rotate the head slightly in azimuth for polar alignment. Much easier than trying to drill a hole and putting another metal post where it would sit directly over a tripod leg.


John :refractor:

#5 gustavo_sanchez

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Posted 14 April 2011 - 10:42 AM

I'm guessing they did it this way at the factory using the theory that 2 legs carry the weight evenly between the 2 thus halving the weight on each leg..Some theories work & some don't.


I don't understand. When the scope is properly balanced, the weight is distributed evenly between all three legs, no matter what. :question:

#6 jrcrilly

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Posted 14 April 2011 - 10:52 AM

It's generally preferred to have a leg under the counterweight shaft so the mount is stable while installing the optical tube; otherwise the unbalanced counterweights could tend to pull the mount over. The only time this isn't done is when the latitude is very low; it can then be necessary to rotate the mount so the counterweight shaft doesn't hit the leg.

#7 Ad Astra

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Posted 14 April 2011 - 11:03 AM

Hi,
I had the same problem with a brand new CGE Pro mount last month... turns out that I had it assembled improperly, but I was amazed that this was possible at all.

The CW shaft needs to be over a tripod leg for maximum stability - especially for long scopes. In this position, the mass is inside the support base of the tripod leg. With the CW shaft between the legs, it is possible to get the weight outside the line of support running between the two tripod feet. I nearly tipped over my Pro mount the first time I assembled it! :foreheadslap:

Glad to hear you have your problem fixed!

Dan

#8 mistyridge

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Posted 14 April 2011 - 11:04 AM

The square azmuth alignment post on the tripod can be moved and screwsd into the hole located at 180 drgrees. This puts the CW shaft directly over a leg. C did the samething on the CGEM. If your tripod does not have the second threaded hole you have no choice but to remove the post as you did.

#9 SkipW

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Posted 14 April 2011 - 11:48 AM

I'm guessing they did it this way at the factory using the theory that 2 legs carry the weight evenly between the 2 thus halving the weight on each leg..Some theories work & some don't.


I don't understand. When the scope is properly balanced, the weight is distributed evenly between all three legs, no matter what. :question:

Not necessarily. When the system is balanced, the center of mass for everything carried on the declination axis (including the axle itself) is at the intersection of the dec and RA axes. On a German equatorial mount, this point can be (in fact, probably is) well forward of the center of the mount's base, which puts the center of mass for the whole system (mount and all) to one side of the center of the mount's base. This will unevenly load the legs; if it's far enough from center to be outside the triangle defined by the tripod feet, it will tip over.

I suspect it was done to avoid interference from the leg when pointing nearly straight up, especially with longer scopes, rather than leg loading, but that's just my guess.

#10 EdTheEdge

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Posted 14 April 2011 - 11:51 AM

The square azmuth alignment post on the tripod can be moved and screwsd into the hole located at 180 drgrees. This puts the CW shaft directly over a leg. C did the samething on the CGEM. If your tripod does not have the second threaded hole you have no choice but to remove the post as you did.


Intersting.... Yes I just relocated mine.

#11 RTLR 12

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Posted 14 April 2011 - 12:24 PM

When I have my SV115T20 mounted on my CG-5 or my CGEM I need to locate the alignment pin between two legs, as it comes from Celestron. Otherwise the scope will contact the legs of the tripod. I could avoid this by the use of an extension, but I find the changed location works fine given the light weight of the SV115T20. However, when mounting my shorter refractors, reflector or SCT I move the pin to the 'over one leg' configuration. It is just a lot more stable this way. This is especially important when doing AP and/or stacking the SCT with a guide scope and all the extra weight that goes along with it.

Stan

#12 Eddgie

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Posted 14 April 2011 - 06:58 PM

Typically, the azimuth lug is placed so that it is over one leg of the tripod.

As mentioned, this is to prevent the tripod from tipping forward if you have a heavy counterweight on it.

For observers near the equator though, what happes is the counterweigths may hit the leg when the elevation is lowered enough for polar alignment.

For those users, it might be necessary to move the azimuth lug between two legs so the arc of the counterweight will dip between them.

Sadly though, this does make the rig prone to tip forward.

No one asked, but I thought I would volenteer the "Why" there is a second option.

#13 Ad Astra

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Posted 14 April 2011 - 11:08 PM

Your explanation elegantly explains a design feature that has bugged me for a long time. Typically, engineers don't do things at random! Now I know "Why???"

Thanks,

Dan

Typically, the azimuth lug is placed so that it is over one leg of the tripod.

As mentioned, this is to prevent the tripod from tipping forward if you have a heavy counterweight on it.

For observers near the equator though, what happes is the counterweigths may hit the leg when the elevation is lowered enough for polar alignment.

For those users, it might be necessary to move the azimuth lug between two legs so the arc of the counterweight will dip between them.

Sadly though, this does make the rig prone to tip forward.

No one asked, but I thought I would volenteer the "Why" there is a second option.








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