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

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

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