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stabilizing a cheap alt-az

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#1 jacobm3

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Posted 12 August 2009 - 11:36 PM

i just bought an orion spaceprobe 3 - http://www.rocketrob...probe3altaz.htm

the optical quality is way better than the cheap department store refractor we had a few years ago, but the mount is really shaky. adjusting focus causes the image to jump and bounce all over the place, as does barely touching the eyepiece by accident.

is there any way to stabilize it, maybe with some weights or something? would a larger dob, like an orion xt8 have that problem?

thanks!
jacob

#2 Luigi

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Posted 13 August 2009 - 06:15 AM

Mounts are as integral to observing as the scope. Larger more stable mounts are generally expensive and it is not uncommon to spend more on a mount than on the OTA (telescope). The point behind the Dob design is to provide a smooth, stable, inexpensive mount for large aperture Newts. A well executed Dob mount will be smooth and stable. Off the shelf Dobs often benefit from a little tweaking to get them a smooth as possible, but the bottom line is the XT8 will be much more stable than the Spaceprobe 3.

#3 deSitter

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Posted 13 August 2009 - 08:17 AM

i just bought an orion spaceprobe 3 - http://www.rocketrob...probe3altaz.htm

the optical quality is way better than the cheap department store refractor we had a few years ago, but the mount is really shaky. adjusting focus causes the image to jump and bounce all over the place, as does barely touching the eyepiece by accident.

is there any way to stabilize it, maybe with some weights or something? would a larger dob, like an orion xt8 have that problem?

thanks!
jacob


Yes - suspend a gallon jug of water from the tripod as follows - make a loop of some strong cord that will fit snug over the legs at about the level of the tray. Use this loop to support the jug in whatever way possible. Try to be unsymmetrical in placing it, to dampen the mode about the vertical axis, where most of the problem arises.

Don't hang the jug from the tray, which might crack or even break the thin plastic struts.

-drl

#4 gnowellsct

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Posted 13 August 2009 - 09:58 PM

drl's suggestion is clever.

another possibility is to substitute wood for the aluminum legs. Some people have the tools and what not to make their own wood legs. Ash is good.

Your scope can also be made into a Dobson with a little ingenuity:

Gil McFarlane's Soap Scope

You have learned the profoundly important lesson that the mount which holds the telescope is an integral part of the optical performance. Odds are your inexpensive Newtonian is a reasonable instrument.

But it won't be worth using till adequately mounted.

Greg N

#5 Pauls72

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Posted 14 August 2009 - 01:19 PM

You are fighting a number of problems.
1) Lack of weight and stability with the aluminum legs. Wood or steel would be the best bet. A gallon jug of water will give you mor problems. If you get any movement in the water it will be very slow to dampen out. Other options are to fill the tripod legs with sand or Quickrete.
2) Flex or movement is another problem. Adding a good spreader helps a bunch to stiffen it up. Take a look at what one of our members Al Canarelli sells in his tripod accessories as an idea for a spreader. He calls it a leg locker.
3) I don't know how much flex or slop there is in the actual mount assembly, but I suspect you have some problems here too. You might be able to tighten up some of the pivot points. With out seeing the mount up close it's hard to say how.

Looking at what needs to be done, you are probably way better off just getting another mount. You can find some good deals on use ones both here on CN and on Astromart's classifieds.

Dob's are very stable mounts.

Here is a picture of what I did for leg spreader.
Posted Image

#6 Deep13

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Posted 14 August 2009 - 01:31 PM

If you use the gallon jug method, don't fill it all the way until you know the tripod will support the extra 8 lbs.

And yes, a commercial 8" Dob will be far more stable.






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