SkyWatcher 200P Collimation Issues

[AweSIM]

hi..

i brought a skywatcher 200p last year.. put it to limited use before i was forced to put it away for almost a year till i finished my studies.. it didnt require major collimation back then but now i feel it needs it badly.. ive tried to follow AstroBaby's collimation guide to the letter but two things make me feel im doing something wrong..

1. stars still dont focus to pinpoints of light..

2. even when ive achieved the sharpest focus i could (pinpoints of light).. i cant get the finderscope to point at the same object as the optical tube..

the finderscope has two adjustment screws.. last year i was able to perfectly align the two things.. this time, when the OTA has the moon in its sight, the moon doesnt appear at all in the finderscope.. this makes me believe that the collimation is out somehow..

ive been trying to collimate it for 2 days now.. trying to collimate it during the day and testing it at night.. im still not close to being satisfied.. any ideas or advice what should my course of action be? i do have a cheshire and sight tube but the sight tube's cross hair wires have become lose.. i do have a laser collimator too but i cant guarantee if its collimated itself or not..

thanks..

awesim..

[Ben Ritchie]

1. stars still dont focus to pinpoints of light..

This sounds like collimation, but can be atmospheric or (lack of) cool-down - if the seeing is poor or the telescope hasn't cooled down to ambient then stars can appear soft even if the telescope is in perfect collimation. There's not much to suggest here other than practice, the Cheshire is a good option IMO and at f/6 the 200p shouldn't be too demanding

when the OTA has the moon in its sight, the moon doesnt appear at all in the finderscope.. this makes me believe that the collimation is out somehow..

This isn't a collimation issue, just that the finderscope isn't aligned with the main tube.

[umadog]

1. stars still dont focus to pinpoints of light..

Not enough information. In fact, stars never focus to a pin-point in any telescope. Light diffracts when it passes through an aperture (your primary mirror in this case), which means it spreads out a little. At higher powers you can see the spread: it's known as the Airy disk. In addition, when the atmosphere is turbulent, stars balloon and bloat. All these things mean you will never see pin-points.

If stars look asymmetrical, that's an indicator that your instrument is not collimated. If they simply don't look like pin-points (but are symmetrical) then chances are that the instrument is collimated.

So examine stars at high power and tell us what you see. In addition, defocus a little at high power (so that you see--hopefully--concentric rings, not the shadow of the secondary). If the rings are concentric you are collimated. If not, you're not. Check out this image: http://lh4.ggpht.com/_F63aizeYQms/SjJmkFf5_UI/AAAAAAAAEx0/HxbW9cN_Py8/s800/star_test.jpg What you see in the eyepiece will look smaller than is suggested by those images.

If the sight-tube's wires are loose then it's useless. You can tell if the laser is collimated. Put it into the focuser and rotate it 360 degrees whilst watching the spot. If return beam (I guess you're not barlowing the laser?) moves by more than a mm across the surface of the target plate then you need to collimate the laser. If it doesn't move then you're laser is collimated. Simple. If it does move then use Google to learn how to collimate it.

[NGC 1502]

There are two issues here, as suggested by the previous posts.

One is collimation of the telescope mirrors, the other is adjusting the finder to correspond to the eyepiece view.

The scope could be correctly collimated, but needs the finder adjustments sorted, number 2 in your posts suggests that could be what you have.

Have you run out of adjustment on the finder ? Maybe the finder has had a knock, you may need to move slightly the finder shoe where it attaches to the tube. If you can, try this in daylight, find a fairly distant object in the main scope, do your best to align the finder with the adjustment screws, if you cant get it close, then what I've suggested could be what's needed.

I'd read and reread the previous posts and think things through.

Hope you sort it, Ed.

[WaveSoarer]

Just to add to Ed's note. Make sure that the rubber ring is correctly fitted on the finder. It will wobble around dramatically otherwise. It took me a little while to work out what the rubber ring was for - no mention in the instruction booklet as far as I can remember. You can also align the finder during the day. Just line up on a distant object at low magnification with the main scope and then tweak the adjustment on the finder. You can fine tune on higher magnification. I usually have to tweak the finder on each session but it usually doesn't need much adjustment.