Quote:
Originally Posted by Aster
Lee
How have you balanced the side by side scopes?
One has to be heavier then the other, unless both are the same size and have the same equipment attached to it.
Imagine a circle, place the side by side instruments, with the centre of the side by side conciding with the centre of the circle, in the circle. Now, do you think if you would rotate the circle that it would stay in one postion if you stop the rotation or would it continue to rotate and find it own balance point, heaviest side of the side by side.
I have found the same problem, does not matter how accuratly you are aligned with the pole, with Newtonians, SMC, etc. if you are not balanced aroung the circumference you will get drift in RA. In one position the heavier side will pull the scope, the drive will be constantly fast, in another position it will be the oposite.
Found that from my own experience, and from others, in 40 years of being in this hobby, a lot of it in deep space photography, the old way, that radial balance is just as important as alignment. Doesn't matter how good your mount is.
For a Newtonian I normally make two end plates with a short stubby shaft, bolt, in the centre. Sit the tube with the endplates attached in a couple of vees. Attach the focuser to the tube and balance around the circumference untill the tube stays, anywhere I rotate it, in place. I then attach the camera, or other equipment, one at a time, and rebalance, etc. The result is, that I now know exactly where and how much weight I have to attach to keep everything in balance. Sliding counterweight bar in the right position, with various weight works wonders, especially in the dark.
SMC and Refractors I used to balance, around the circumference, by having a board with two ball bearings, arranged in a vee, at both ends of the board. Sit the instrument on the ball bearings and watch it rotate of its own accord. the counter balance.
Two side by side instruments are harder to balance but the above might give you some ideas.
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You might have hit the nail on the head Alex!
I have a similar prob with my newtonian in a side by side setup. The guidestar does not shift in PHD guiding but between every image there is a slight image shift always in RA just like what Lee is getting and I have contributed that to flexure in the OTA. But that flexure might originate due to the OTA not being balanced correctly?
Having a heavy focuser and a DSLR attached to one side of the tube would make it heavy on one side of the OTA. Maybe I should attach a counterweight opposite the focuser?
Do you have a pic of your side by side setup Lee? may help?
cheers Gary