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Post by Dave.B on Jun 16, 2005 13:05:20 GMT -4
What telescope and mount do you have? I don't know what sort of mount it is - it swings round rather clumsily in the horizontal plane, but has has a fine adjustment in the vertical plane - I guess that's an altitude-azimuth arrangement? Maybe you could explain to me how the Equitorial mount works? I'm a little disappointed with the mount TBH, but the telescope itself seems pretty good. As for the telescope, it says "D=76mm F=700mm" on the side, and it's a reflector. Can you tell I'm an amateur?! ;D Luckily my garden has a very wide and unobstructed view of the sky from south-east to almost north, so there's plenty of stuff to look at.
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Jun 16, 2005 14:08:00 GMT -4
As for the telescope, it says "D=76mm F=700mm" on the side, and it's a reflector. Hmm... that sounds more like a refractor. D=76mm is the diameter of the objective lens or mirror, and F=700mm is the focal length. A 76mm (3-inches) lens is very common for refractors, while most reflectors start at about 4.5-inches. I don't think I've ever seen a reflector as small as 76mm. I don't know what sort of mount it is - it swings round rather clumsily in the horizontal plane, but has has a fine adjustment in the vertical plane - I guess that's an altitude-azimuth arrangement? Maybe you could explain to me how the Equitorial mount works? Your description sounds like an altazimuth mount. An equatorial mount has one of the telscopes two axes aligned with Earth's axis of rotation. In this configuration one of the telescope's axes moves north-south (declination) and the other east-west (right ascension). Tracking an object as it moves across the sky requires that the telescope be rotated around the right ascension (RA) axis only. Often the RA axis is equipped with an electric motor that exactly counteracts Earth's rotation to keep objects centered in the field of view. Furthermore, the axes of an equatorial mount move in the same directions as the coordinate grid of a star chart, thus I find it easier to use the telescope and chart together to find faint objects. The drawback of equatorial mounts is that they are bulkier and more expensive than altazimuth mounts. I see very few equatorial mounts on amateur telescopes over 10-inches. The following Web page gives some good information about telescope mountings: www.spacegazer.com/types-of-mounts-1-g.asp
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Post by Dave.B on Jun 16, 2005 16:33:27 GMT -4
Bob, thanks for the link and the info. I may be getting confused between the Reflector/Refractor thing: mine is one where you look through the side of the telescope - it has a big mirror at the the back end of the tube, and a little thing (prism?) in the middle of the front opening. I always that was a reflector and a refractor was a straight, look in at one end and out the other?
Actually, I just checked the site you linked to and mine's a Newtonian one. Must be just an unusually small one. Anyway, no point getting it out tonight as it is very overcast. I'll probably just read that site instead...
Cheers
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Jun 16, 2005 16:58:52 GMT -4
Yep... based on the description yours is definitely a Newtonian reflector. I've just never seen one that small before, unless the D=76mm means something other then I think it does. Does the diameter of the mirror look to be 76mm?
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Post by Dave.B on Jun 16, 2005 17:13:58 GMT -4
I haven't measured it, but yes, 76mm would be be about right for the diameter of the mirror. I've just been reading that site, and now I've got a hankering for a motor driven German Equatorial mount, complete with PC cooling fans to remove the chimney effect!
One step at a time I suppose. Next clear night that comes along, I'll be out looking for Saturn.
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