Well, I’m still using the telescope described in this thread. Now I’m ready to move on to fixing some of the other problems I have with this scope. The number one problem being, vibration. This mount is on a steel pipe rather than the tripod most people seem to have, and the tube is aluminum, which seems to be extremely prone to long lasting vibration. I’ve seen the little pads for the tripod feet, but I believe my problem here is the tube, not the mount. I’ve got a few ideas, but I’ll bet the teemings have more. Perhaps wrapping the tube in something?
Oh, and for those who wonder why I don’t frequent an astronomy board, I have to say that I only have time for one board. And this is it.
Some photos might help here. My guess is much of the vibration is due to elasticity in the joint between the tube and the mount–a common problem with older, or less expensive mounts. Which mode of vibration seems most prevalent?
What are you resting it on? The best is to set it up on the ground. If you’re setting it up on a wooden deck or porch, you’ll get vibrations when you walk around the scope.
First, in relation to your previous thread, you should know that an alt-az mount does not need alignment. Even if the telescope comes equipped with setting circles, they are not made to be used with an alt/az mount. They are meant for an equitorial mount only, and even then…alignment is only needed if using a clock drive. Simply use your telescope as a “point and shoot”. The finderscope and a star map is your best friend!
Next, vibration is next to impossible to conquer. Toy store telescopes are especially vulernable turning many people off to astronomy because it is so frustrating. But, with patience, I have even discerned the rings of Saturn with a small, toy store reflector. Of course, every little breeze seemed to whisper trouble as I tried to observe with an unstable mount.
As for the mount, I have seen the kind of mount you mean. Usually, such mounts are for scopes to be placed in an observatory as opposed to one meant to travel. Anyhow, you might contact a university’s observatory or science museum to see what they might recommend. Personally, a stable mount can make you or break you…and then you have the optics to deal with. You’d be surprised, though… often the fancier scopes you can find at the larger Wal-Marts (as opposed to toy stores) offer adequate optics and a stable mount for a reasonable price. This should appease your needs for now without hurting your wallet.
If you dream of doing more serious observing, look into a casseigrain scope with clock drive. This will accomodate some astrophotograhy, even, with the right accessories. (A friend of mine found one used and the owner let him try it out - check the back of Astronomy or Sky and Telescope magazine for such ads.)
Over and beyond this, make sure your skies are dark enough before shelling out major bucks for deep sky observing equipment.
OK, a bit more info: the mount is, in fact, and equatorial, not alt/az. I didn’t know the difference when I got this telescope.
The surface I set up on is solid reinforced concrete. I don’t think that is the problem. The vibration seems to be coming from the aluminium tube; I considered the steel rod holding the secondary mirror, but I think the stiffness of the rod would preclude vibrations of the low frequency that I’m seeing.
I’ll go out now and take some photos, and as soon as I can figure out where to post 'em, you’ll get to see them.
Sign up to the Cloudy Nights message board and post there. Their message board allows you to upload images, and it’s more on-topic anyway. (Yes I know you said you don’t have time for another message board, but it’s your own loss if you don’t make the time.)
The first thing I’d do is check for play on the various parts of the mount. If there seems to be none, it might very well be the tube. How thin is the aluminum? Does it seem very flexible, or is it quite stiff?
It’s just over .055 thick. Pretty thin, ringy stuff. I’ve thought about a resilient material between the tube and the mount, like 1/16" hobby foam. I think part of the problem may be that the mount/tube interface is too stiff.
You could try stiffening the tube. I’m thinking something like heavy-gauge steel or hard brass strips riveted allong the length of the tube. This would provide support on the long dimension, where most of the flexion is occurring. Pop™ rivets are easy to use and pretty inexpensive. Naturally, you’ll need to protect the mirrors from drill shavings when drilling the through holes.
Actually, I’m now considering calmping a bit of padded bed rail (angle out) along the length of the tube. No damage to the tube, and reversable. I’l try it out tonight.
Just to comment on this, even without a clock drive, alignment can be useful on an equatorial mount. It’s much easier to track an object manually if you only have to move the scope along one of its degrees of freedom, and a person used to equatorial or alt-az might have a difficult time slewing with an axis in a different direction. At least point the axis roughly north.
You might want to try a few simple experiments to isolate the source of the vibration. Perhaps you could try setting the optical tube assembly (OTA) on the ground, pointing straight up, and see if the vibration is still there. This will tell you if it’s in the OTA or the mount.
Once you’ve isolated it to either the OTA or the mount, you can try exciting the vibration by tapping on various parts of whichever one seems to be the problem. You’re looking to excite vibrations of the same frequency and duration as the ones your trying to get rid of.
One possible source is the rather long, thin arm holding the counterweight. Another is the joint between the polar axis and the pier.
Even a light thin-walled aluminum tube is pretty stiff, so the pier itself wouldn’t be high on my list of suspects, although the joints at either end may be loose and causing a problem.
It’s too bad you don’t live near me. I have about 7 or 8 3’x6’ (or was it 4’x6’ ?) 1/4" thick steel plates I’m trying to get rid of, that were used to cover an access trench in an industrial building I manage. We filled the trench with concrete so now the plates are redundant. Might have made good stabilizers for the tripod as they are very heavy. I had to struggle to lift and tilt one upright. You could also line your walls with them if you live in a bad neighborhood as I’m sure they would stop most small arms fire. .
weld some two inch spikes on the end of the three legs so they dig into the ground and fill the tube with lead shot or concrete - that ought to firm things up a bit.
If I stand it straight up, the modes of vibration (band name!) that are available while on the mount will not be available. Thanks for the thought, though.
