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Celestron C8 and collimation
Hello,
I've been lurking for a bit now, nice to see such a variety of people here! I had a small question. My Dad gave me his Celestron C8 that he bought some time ago. It has never been collimated, and not only that but it was knocked over once. So, I dont get to see any stars, only little arrows (missed out on Mars as well). I've been reading a few sites on collimation, and all seem to be pretty good information, however, I cannot find any place that tells me how to get into the scope to do the adjustments. I was going to take it to someone, but it seems there is nobody here local any longer (Spokane, WA). Would anyone have any tips on where to start? I don't have the paper manuals that came with it, and the online PDF doesn't seem to have anything either. Thanks in advance! Jon |
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Jon Hunter wrote in alt.astronomy:
I had a small question. My Dad gave me his Celestron C8 that he bought some time ago. It has never been collimated, and not only that but it was knocked over once. So, I dont get to see any stars, only little arrows (missed out on Mars as well). I've been reading a few sites on collimation, and all seem to be pretty good information, however, I cannot find any place that tells me how to get into the scope to do the adjustments. I was going to take it to someone, but it seems there is nobody here local any longer (Spokane, WA). Would anyone have any tips on where to start? I don't have the paper manuals that came with it, and the online PDF doesn't seem to have anything either. If you're going to collimate it by hand, the procedure is not too tough. You don't have to remove anything but the little cap over the secondary mirror. You certainly don't have to open the tube. A C8 is collimated by tiny adjustments to the secondary mirror - on the outside. (If the correction plate (front "lens") never has been removed, that's good, as it must still be in the right position. If you ever feel the urge to remove it, be careful, there are some cork supports that should be returned to the exact, same place as it's important for the collimation as well. But it should largely be unnecessary) The secondary mirror of course is located in the middle of the corrector plate. Carefully remove the cap of the secondary mirror, and you'll see three screws. By adjusting these screws ( I guess in your case with a hexagon socket wrench) you can collimate your scope. Point your C8 to a bright star - not a planet - and move it far out of focus. Now you should see the star become distorted to a ring with a black spot in the middle. That's your secondary mirror. You should also see some concentric rings. The black spot should be exactly in the middle, and the concentric rings should encircle each other perfectly. If it's not perfectly in the middle, start adjusting the image with carefully turning the screws. Remember to give each screw an exact small turn (say one-eight turn) each time to see what happens. So you'll be able to correct it when it happens to be the wrong screw or the wrong side you turned to. Take your time and do it with very small steps. It's imperative you don't tighten the screws too much, because it will damage the secondary mirror. Don't force anything. It's precision work. And be careful not to hit the plate with the socket wrench / screwdriver, so - second time - take it easy. To see examples of the star image (on this case computer generated Airy disks) you should see, go to this page: http://perso.club-internet.fr/legault/index.html and click on "collimation" in the left frame. Now scroll down and see the pictures. It can be that you see slightly different images getting out of focus to both sides. -- CeeBee Uxbridge: "By God, sir, I've lost my leg!" Wellington: "By God, sir, so you have!" Google CeeBee @ www.geocities.com/ceebee_2 |
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On Sun, 07 Sep 2003 07:13:55 -0700, CeeBee wrote:
If you're going to collimate it by hand, the procedure is not too tough. You don't have to remove anything but the little cap over the secondary mirror. You certainly don't have to open the tube. A C8 is collimated by tiny adjustments to the secondary mirror - on the outside. (If the correction plate (front "lens") never has been removed, that's good, as it must still be in the right position. If you ever feel the urge to remove it, be careful, there are some cork supports that should be returned to the exact, same place as it's important for the collimation as well. But it should largely be unnecessary) snip Thank you so very much! All this time, I never knew (but always wondered why it was a bright orange cover!). This has helped me greatly. I really appreciate the detailed helped! Maybe now I can start enjoying the telescope, instead of getting frustrated! Jon |
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