Laser Collimation Vs. Collimation Cap

[Arcane]

Hi there. I received my telescope yesterday and unfortunately it has been cloudy so I haven't been able to use it yet, but I did set out to collimate it.

I have an 8" dob reflector made by Orion, SkyQuest XT8 model to be exact.

Anyway, so I set out to collimate this thing having never collimated a telescope before. I used the Collimating cap first and finally go it to where it looked perfectly lined up. Then I used the laser collimator to see how accurate my results were. Well, to my dismay, according to the laser everything was WAY off. So I lined everything up perfectly with the laser. Then I put the collimating cap back on and to my even greater dismay, everything was completely screwed up. I couldn't even see half of the main mirror and secondary mirror was all of kilter as well.

So my question is, is my laser collimator messed up, or not accurate?

I set everything back into alignment with the collimating cap and took it outside to look at some near objects (maybe half a mile away, which I know is not a good test) and everything looks fine and crystal clear. So it only leads me to believe that the laser collimator is not working properly.

It says in the instructions that if dropped or roughly handled the laser could become misaligned, so maybe it was dropped during shipping...

I have done a lot of reading on collimating and I am sure I am doing it correctly, but I just can't believe the laser is off by that much.

Thanks for any input.

[SanitysEdge]

The collimator sits very loosely in the focuser. Too loosely to get any sort of accuracy out of it.

Also, congratulations on the XT8. I got mine about a month or so ago. Ive used it every clear night since and I love it. Its also my first (decent) 'scope.

[Arcane]

Cool man. Not to get off subject, but how are the views in this thing? Do you use a Barlow and did you get any other lenses or are you just using the two sent with the scope?

Back to the subject. Are you saying the laser collimator is completely useless because there is play in the focuser slot it goes into?

The good news is, I called up Orion and told them I thought the Collimator is not functioning properly and without hesitation he said they are going to send me a new one. I didn't even have to go into detail about what I thought was wrong with it. And I don't even have to send back the one I have. Man, talk about customer service!

I guess I will just have to wait until I get the laser collimator and try collimating with it to see what the real issue is.

Thanks for the response. Any more input is appreciated!

[Arcane]

I just checked out the fit of the collimator again and it does have a tad bit of play if you just set it in the hole without tightening it up. However, if you tighten it up in there it is very steady. BUT, maybe that tad bit of play is forcing the collimator off to one side when it is tighted up just enough to make it no perfectly centered.

Hrmm, interesting.

[SanitysEdge]

I got a celestron E-Lux 6mm eyepiece which gives me a magnification of 200x to help with planets. I find that higher magnifications really help with mars to help disperse the brightness. Mars is bright at lower magnifications and it washes out the detail. Even with the 6mm eyepiece its still pretty bright and I find the best views of it are when light clouds roll in front of it. Id like to get a barlow but I'm not sure about which one to get.

The first time I looked at the orion nebula I almost passed out because it was so awesome. The amount of detail that is resolved over my old crappy scope, a 60mm tasco refractor, is incredible. I don't really have any other telescope to compare it to other than a bottom of the line tasco but overall I am very impressed. I wish it wasn't so cold outside so I could stay out longer at night and use it more often.

As for the collimator, I was reading up about it when my scope arrived and found that you could make it more accurate by putting a layer of scotch tape around the part that sits in the focuser to reduce play. I haven't tried that yet so I don't know how well it will work.

[Arcane]

Well, I got the new laser collimator today and it is doing exactly what the other one is. It is a good 2 inches off the center of the primary mirror. If i collimate it to line up with the laser I wouldn't be able to see anything out of the scope.

There is a very tiny amount of play in the fit, but that is to be expected since if it was any tighter it would be really hard to fit in the hole. No matter how I jiggle it in the slot there is no way to line the laser up even close to where it should be.

I am just at a loss for words on how this laser collimator could be so badly off. I thought they were supposed to give you perfect precision, not be so widly off as to be unusable.

But any way, they make fun toys for playing with the dogs heh.

[RickJ]

Something is wrong with your collimation. Best to find a club in your area and let one of the guys take a look. If you rotate the laser and it stays way off then collimation is off. Could be the focuser isn't at right angles to the tube, the secondary isn't where it belongs or is tilted. I assume when you say it is 2" off you mean it is hitting the mirror 2" off center. If it is hitting the mirror's center but is 2" off on the return then the main mirror is tilted.

Anyone in a local club will be able to tell you in a couple seconds where the problem lies.

Rick

[Arcane]

yah it is 2" off center of the main mirror. I have collimated it to line up ecaxtly perfect with the laser on both mirrors, but when I do that the scope is unusable. And I get great crystal clear views of the moon by using a cillimating cap and when I do a star collimation test I get perfect circular rings, so someting makes me think it is a problem with the laser moreso than the collimation.

It would be nice to have someone with years of experience look at it. But I doubt I will have the time or gumption to drag it to some stranger in a club to look at it.

Thanks for the suggestion though, I may end up doing that eventualy if I notice any real collimation problems when viewing other objects.

[aurora]

Well, I got the new laser collimator today and it is doing exactly what the other one is. It is a good 2 inches off the center of the primary mirror.


I'm with RickJ, not sure what you mean. If you mean that the red dot is 2 inches away from the center of the primary mirror, then how would you adjust it? Should be with the adjustments on the back of the primary mirror, and not with the adjustments on the secondary or on the focuser (which should have been aligned already).

If the above is the case, then I can't fathom why that adjustment to the primary would result in you not being able to see anything out of the scope. Which leads me to suspect you are adjusting the secondary instead of the primary at a middle step in the collimation process.

[aurora]

yah it is 2" off center of the main mirror. I have collimated it to line up ecaxtly perfect with the laser on both mirrors, but when I do that the scope is unusable.

That is possible to do, depending on the order in which you do the collimation steps.

Just to double check that it isn't the focuser, here's a question. With the laser collimator in the focuser, what happens to the red dot on the primary as you move the focuser in and out?

[Arcane]

Moving the focuser in and out has no affect on the placement of the laser on the primary mirror.

[RickJ]

Rotate it in the focuser. If the laser is bad (highly doubtful) the spot will rotate in a circle on the primary mirror. If it stays in one spot the laser is fine. Use the site tube to put the center of the secondary on the cross hairs then tilt the secondary until the cross hairs are centered on the primary. At this point you should see the circle of the edge of the sight tube, the circle of the edge of the secondary and the circle of the far end of the tube and the circle of the outer edge of the main mirror are all perfectly concentric. Each slightly smaller than the next closer to your eye.

First adjust the secondary up and down the tube until it is concentric to the sight tube's edges (not user adjustable in some scopes-check your manual), then adjust its tilt until the tube and mirror are concentric. If this is done right the laser should now hit the center of the main mirror or very close. If off slightly (yours is WAY off) you can safely adjust the tilt of the secondary to bring it to the center of the mirror.

Once the sight tube says all is fine then adjust the three screws on the main mirror to move the reflection of the secondary to the center so it is concentric with everything else and dead on the cross hairs. Now the laser should it the center of the main mirror and its reflection double back perfectly on itself. If it misses the center of the main mirror slightly then tweak the tilt of the secondary. Then if it doesn't perfectly double back on itself you can tweak the main mirror until it does.
At f/6 a small error in collimation is not a real problem but what you describe sure is.

Again, this is an issue quickly solved if you join a local club, they usually have a member or two assigned for helping in just this type of situation. This is easy to fix with access to the scope, nearly impossible via keyboard.

I would think the Orion manual covers all this. But it can be confusing the first time. Few of our members mastered it from instructions on the net or with the scope. It is something easily grasped once someone leads you through it once and you actually see what you need to see and what to ignore.

Rick

[Arcane]

Hey Rick, thanks for the reply and sorry for the delayed response, I've been out of town. But I will try to follow your instructions here.

Rotate it in the focuser. If the laser is bad (highly doubtful) the spot will rotate in a circle on the primary mirror. If it stays in one spot the laser is fine. Use the site tube to put the center of the secondary on the cross hairs then tilt the secondary until the cross hairs are centered on the primary. At this point you should see the circle of the edge of the sight tube, the circle of the edge of the secondary and the circle of the far end of the tube and the circle of the outer edge of the main mirror are all perfectly concentric. Each slightly smaller than the next closer to your eye.

Ok I did the rotation thing with the laser and one of them is bad, the laser rotates in a circle as it is turned, but the new one does not. However, when I stick either one in they both point at the same location, about 2" off center of the main mirror.

When looking thru the site/focuser tube I see everthing in perfect alignment. Even when using the collimation cap everything is perfectly centered. I see the main mirror with the secondary mirror centered, the focuser tube centered in that and the dot in the center of the mirror centered on that and the hole in the collimating cap centered inside that hole. Everything looks perfect.

First adjust the secondary up and down the tube until it is concentric to the sight tube's edges (not user adjustable in some scopes-check your manual), then adjust its tilt until the tube and mirror are concentric. If this is done right the laser should now hit the center of the main mirror or very close. If off slightly (yours is WAY off) you can safely adjust the tilt of the secondary to bring it to the center of the mirror.

This is where I lose you. The secondary mirror seems to be perfectly concentric to the site tube, no adjustment was needed. The laser is in the same place. So I am not sure what to do.

If I move the secondary mirror so the laser aligns in the center of the primary mirror then the secondary is no longer concentric with the site hole.

Anyway, thanks for you help and patience.

[RickJ]

If one laser makes a circle but the other doesn't yet both hit the same spot doesn't make sense to me. A circle defines an infinite number of spots, all different. You mean the new one hits a spot on the circle the other one made when rotated? Even that doesn't make sense as the correctly aligned one (doesn't move when you rotate it) would be in the center of the ring or at least near to it.

This is one of those many cases that a fellow from a local astronomy club could solve quickly but makes little sense from a distance.

For now go with the eyeball. Then when seeing is good look at a star in the center of the field at high power just out of focus. It should be round with a dot in the center with some dark concentric circles around it. How many depends on how far out of focus you are. The farther out of focus the less sensitive this test is. If you have 2 or 3 rings and they are concentric when the star is centered you are in great shape. When seeing is lousy seeing this can be difficult however.

Rick

[Arcane]

Right. Thanks Rick. I have done the Star test and I get concentric rings like you described. What is going on with those lasers I don't know, but I am determined to find out. Maybe I will find a local club or astronomy store that has someone who can check it out for me.

Thanks mate!