Expert: Tom Whiting - 8/6/2007

Question
I have many questions, especially about cosmology & deep space, but right now you're my only resource for a little problem I have. I hope you can help. I just had first light on my 'new' Antares 14.5" truss dob. It has a bit of 'rebound' when I try to position it on the object - that is, I push it into position but when I release it the object moves out of the FOV (laterally). I don't want to start oiling, greasing or disassembling until I get an idea from someone with experience as to what I can, should, or should not do to correct this (if possible at all). I got the scope used, but I believe it to be in great shape; it could be I just don't have enough experience and will simply have to adapt. I appreciate your thoughts on this. Thank you.

Answer
Hi Tom,
Sounds like either a simple balancing problem or perhaps
you aren't setting up on a very level piece of ground.  Balance problems can be solved by simply adding weight on the mirror end, or adding additional weight on the diagonal cage.  You can easily check for balance by placing the scope at both a high angle and a low angle, and see if the scope maintains, without drifting up or down, it's present position.

If it's an azimuth problem, which appears to be your problem, usually it's because your scope isn't level, and/or it's TOO free to move in azimuth.  In your case it sounds like the azimuth bearings are TOO free to move,  and TOO well oiled.  In that case, you need to add some resistance....the simple addition of a couple of teflon pads on the bottom of the  rocker box riding on the "other" surface will provide enough resistance to stop the backlash drift, while still providing a smooth operation.  You know your scope is too free-wheeling (in the azimuth) if the slightest breeze, say 5 mph, causes the scope to weathervane.  Any scope should stay perfectly still in a 5-7 mph wind.  Fortunately, it's easier to solve this problem as opposed to too much resistance.  But, even with the addition of a couple of teflon pads, if the scope still
"rebounds" then it's just a matter of adapting to that amount
of rebound.  With my own 30 inch truss, I have a similar
problem with the altitude bearings...I already know it will
"drop" about 1/8 degree when I release it (probably due
to it's large size) so I always aim just a tad high on an object
then when I release it, the scope will "drop" right on the selected object.....each scope is slightly different, but with time and practice, you get used to it.  But in your case, I think it's a simple problem of providing just a touch more of azimuth resistance.
OR, perhaps the azimuth bearing has TOO much lubricant, so
you need to remove some oil, to "tighten" the movement
up a bit.  Maybe this would work instead of, or in addition to, installing the teflon pads.
Hope all this helps,
Clear Skies,
Tom Whiting
Erie, PA
PS...Antares scopes are currently one of the finest optical
instruments made, in addition to Orion and Discovery scopes.  We highly recommend Antares Scopes to our new
members, in fact, my 6 inch finderscope on the 30 inch is
an Antares model, and I find it has outstanding optics.
And if you have any further questions, please feel free to
contact me directly at bwhiting@velocity.net



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