Problems with Collimation

[SkyGuy228]

I got an Orion Dobsonian XT-10. I'm using a laser collimator and when I get everything aligned, I come to see that the secondary mirror is slightly rotated and the offset is at 45 degrees off to where it needs to be. I spent over 5 hours trying to correct this yet it keeps ending up in the same spot! I tried turning the screws ever so slightly, but those 3 adjustment screws seem to always cause the secondary mirror to rotate to the same spot over and over again! Any ideas to what's wrong?

[jetstream]

I'm not trying to dis your equipment, but buy a Cheshire collimator, problems will be over. I use one with my 10"  f4.8 and collimation from scratch after reinstalling mirrors is about 5 minutes.

The Cheshire "automatically" provides the proper alignment for the secondary offset (one) and makes it easy to "get it round"... obviously we still make manual adjustments to the mirrors using the Cheshire as a guide. Your sec holder may have divets worn in it that the screws keep coming back too. Hold the stalk while adjusting and then snug with the centre screw.

[SkyGuy228]

Tried holding it in place. Also tried it with a friend holding it, but the stupid thing keeps rotating!

[SkyGuy228]

And I don't think it has anything to do with the collimator tool. The adjustment screws keep rotating the mirror.

[jetstream]

Well, have you heard of the " milk jug washer trick"? I don't use one but many do it seems... I'm sure someone who does will be along!

[SkyGuy228]

No, what is that? I was thinking about going to home depot to buy some washers to put between the mirror and the screws.

[jetstream]

Basically you cut a washer out of the milk jug plastic so the screws contact it and not the stalk (divets) - are the divets so deep that holding sec colli won't happen?

[Qualia]

Aye, the Moonshane Plastic Milk Bottle Wonder 

I don't care if the idea was whispered elsewhere in the esoteric caverns of dark collimation secrets, Shane carried the light and passed it on to mere mortals like ourselves .

Not being a previous owner of a reflecting telescope, I used to wonder what those two little white disks of milk bottle plastic were sitting under my secondary. After collimating the secondary for the first time, I thought to myself what geniuses were the manufacturers! How tight everything remains, tilt and tweaks rock steady at all times! I had no idea that this effective addition was a homemade mod!

It's quite simple and will save you a lot of grief. Using a standard plastic milk bottle, you cut two circles the size of the secondary holder (where the big screw keeps it in place) and put a hole in the middle of each one (so the screw goes through) They work superbly and make fine tuning the secondary a breeze.

[SkyGuy228]

Cool! I'll give that a shot! THanks!