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Refractor/Mount Question
In article , Alan W Craft wrote:
Here is where I'd like to ask: Should the weight of the counter equal or at least approximate the weight of whichever O.T.A. one decides to mount? Will my 11 lb. O.T.A. require an 11 lb. counterweight to balance it, or would the commonly-included 7-8 lb. counter suffice? I understand that the counter may be slid up and down its shaft to compensate, but would an exact match in weight between the counter and O.T.A. be the ideal? To balance you need m*d to equal M*D where m is the mass of the telescope and d is the distance from the center of mass of the telescope to the polar axis, and M is the mass of the counterweight and D is the distance from the center of mass of the counterweight to the polar axis. To minimize vibration you want d and D to be as small as possible. Once you've bought your telescope d is fixed by the design of the mount and you can vary D inversely with M. You also want to stay within the weight capacity of the mount by minimizing m+M. The capacities quoted by some manufacturers are optimistic. Sometimes it seems that they mean the weight that just fails to collapse the mount. |
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Refractor/Mount Question
On Thu, 10 Jul 2003 23:50:49 GMT, William Hamblen ...reflected:
In article , Alan W Craft wrote: Here is where I'd like to ask: Should the weight of the counter equal or at least approximate the weight of whichever O.T.A. one decides to mount? Will my 11 lb. O.T.A. require an 11 lb. counterweight to balance it, or would the commonly-included 7-8 lb. counter suffice? I understand that the counter may be slid up and down its shaft to compensate, but would an exact match in weight between the counter and O.T.A. be the ideal? To balance you need m*d to equal M*D where m is the mass of the telescope and d is the distance from the center of mass of the telescope to the polar axis, and M is the mass of the counterweight and D is the distance from the center of mass of the counterweight to the polar axis. To minimize vibration you want d and D to be as small as possible. Once you've bought your telescope d is fixed by the design of the mount and you can vary D inversely with M. You also want to stay within the weight capacity of the mount by minimizing m+M. The capacities quoted by some manufacturers are optimistic. Sometimes it seems that they mean the weight that just fails to collapse the mount. I'd like to place a Parks 8-inch f4 "Nitelight" on a Vixen GP-DX, but thus far the only place I've seen the weight of the Parks O.T.A. even remotely specified is here... http://www.astro-optics.suite.dk/supnew.htm ....but I believe that the Parks rotating-ring system is included in the 13 kg. specification. I would, of course, use the non-rotating Vixen rings which should weigh somewhat less. With the GP-DX load capacity rated at 10 kg. I would defintely be pushing it, that is, if I incorporated Parks's rings which I wouldn't. Now off to hunt for the weight specification of ONLY the O.T.A. Alan |
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