Collimation help

[gooseholla]

No matter where I tilt, or twist or move the secondary mirror to, it is incapable of showing the three mirror clips together in one image - no matter what the position of the focuser or cap. Help!

[umadog]

The mirror clips will not all be visible if the secondary is too small or if you're looking at it from too far away. Examine the reflection of the primary. Does it look like it is larger than the secondary? If so, you won't be able to see the 3 clips at the same time. I this case, ignore this step of the procedure and do everything else. You'll lose a little light but it won't matter terribly much and you can still get good axial alignment, which is what really counts.

[gooseholla]

I fear I may have to get someone to actually show me the first time how to do it, and how to do it best with the constant shifting of the focuser.

[umadog]

Why is the focuser shifting? What do you mean?

[gooseholla]

Fully racked in, it is one position - say if you were dead centre on the primary spot. Move it 2mm or so up, and it shifts to a different position (say the spot moves down in the view a cm or so) - it will then stay in that position until it is fully extended, where it will then move again. However, if you are drawing it up and then decide to rack it back in, it then shifts to a different angle again ( say the spot moves up a cm or so and then left a bit).

However, it shifts quite radically sometimes, and can mean that the central black spot is now way off the centre of the eyepiece tube.

[AlBoning]

If using a sight tube it could be that it is too long. A properly sized sight tube has the same ratio of length to diameter as the focal ratio of the primary mirror.

[gooseholla]

Well I purchased - albeit a 2nd hand one - the celestron one for a celestron scope. However... I seem to have, via trial and error, got it pretty damn close - the views are definately sharper.

[umadog]

Collimate it with the focuser in roughly the position you would have it when viewing. This sort of thing can happen at the extremes of focus, especially with a cheaper focuser. Collimation doesn't have to EXACT for your image to be good. There are tolerances. Your goal is to get it looking as good as possible so that if slop does occur in the mechanics of the scope, these will hopefully not exceed the tolerances.