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Balancing

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#1 hamdul

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Posted 07 July 2013 - 11:22 AM

I read a lot about balancing so yes I've put everything on the tube, Dew shield, Eyepiece. Finder et al. Then did the pencil thing to find the balance point. Now comes time to secure the tube to the mounting bracket. I have not seen anyone say where that should be. Where should the balance point be relative to the mounting bracket? :question:
Fred

#2 Midnight Dan

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Posted 07 July 2013 - 11:54 AM

Hi Fred:

For perfect balance, it would be right above the top of the pivot point when the OTA is horizontal. However, you really don't want perfect balance.

The issue is that the gears in the scope have a lot of slop, known as backlash. You want the OTA to be a little off balance so that it preloads the gears by pushing against them in one direction or the other. To accomplish this, put the balance point of the OTA about 1/2 inch to one side or the other of the pivot point on the arm.

Next question, of course, is which direction? If you move the OTA forward to get that 1/2 inch offset, you can run into a problem of shifting weight. When the OTA is horizontal, several of your accessories are above the centerline ... such as the finder and the eyepiece sticking up from the diagonal. This upward offset doesn't affect balance one bit when the scope is horizontal, but when the scope is vertical, they do! At zenith, these items are now positioned behind the pivot point and contribute to a rear heavy scope. So if you placed your OTA 1/2" to the front, at some point when you raise the OTA towards zenith the weight can shift to the rear. When that happens, the slop in the gears can allow the OTA to suddenly move a small amount upward. You probably wouldn't notice it, but it would definitely affect alignment.

So, from a weight distribution standpoint, rear-heavy is better. As you raise the scope to zenith, the shifting weight due to top mounted accessories with just add a bit more rear-heaviness, but the preload against the gears will be maintained in the same direction. Unfortunately for many of us, putting the balance point of the scope 1/2 inch to the rear means that the diagonal will contact the base at zenith. This is especially true if you have a 2" diagonal.

Bottom line ... go rear-heavy if you can clear the base, otherwise go front heavy.

-Dan

#3 Tel

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Posted 07 July 2013 - 11:58 AM

Relative to the Altitude GoTo Approach setting you choose, Fred.

Thus, If you choose a Negative Altitude GoTo Approach, place the OTA a little forward of your (pencil) balance point in the dovetail shoe.

Conversely, if you choose a Positive Altitude GoTo Approach setting, place the OTA slightly back, (towards the mount), of your (pencil) balance point when setting it in the dovetail shoe.

Whichever might be the better is a matter for you to decide. Try both and establish which setting is better for you.


Also remember that as a Northern Hemisphere dweller, your Azimuth GoTo Approach should be set to Positive.

Hoping this helps,

Best regards,
Tel

#4 Bob Griffiths

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Posted 10 July 2013 - 07:07 AM

By a little bit forward or backward of the balance point SEEMS to be between 1/8 and 1/4 of an inch from my own experience.. NOT a heck of a lot..

Personally I run mine rear end heavy Both Tel and I run 8i not 8Se's and both of us use Rays Bracket when we mount out scopes on the OEM mount...

No clearance problems even at Zenith

Bob G






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