Collimation secondary Mirrors?

[TwistedJester]

Im currently collimating my Dobsonian Skywatcher 200P. Im on to the part of the 3 secondary mirror tilt screws. How much of the three parts from the secondary mirror is ment to be visable when looking thrrough cheshire?

Thanks

[scuffer]

Do you mean the 3 clips on the primary ? I have just had my first attempt and couldn't get all 3 clips in view using my Cheshire so I am going to source a 35mm film container for this part . Google astro baby's collimation guide

[LukeSuppalot]

The secondary mirror is the one nearest the focuser. The primary is the one with the clips holding it in place.

When you look through the Cheshire you should be able to see part of the clips. It doesn't matter how much of the clips you can see, just the same amount of each.

I agree with Scuffer, Astro Baby has a good guide thats easy to follow.

Luke

[Black Knight]

Astro Baby's collimation guide is here: http://www.astro-baby.com/collimation/astro%20babys%20collimation%20guide.htm

[TwistedJester]

Thanks for the replys. I have been using astro babys guide, and have been trying to collimate for about a week. I have the crosshair of my cheshire fairly central to the circle on the primary mirror. And the secondary mirror is quite central to the focus tube however I can only see one of the primary mirror clips. Is this ok or is it a mt to see all 3?

[umadog]

This particular instruction seems to generate the most confusion. The guide should probably be modified. This is what you need to know.

You want to be in a situation where you see all of the primary when looking from the peep-hole with the peephole at the focal plane. If you can't see all of the primary then you are loosing some light. Probably not very much light, but some light. One way to explain this to people is to tell them to get all three mirror clips in view. This is just an easy was of getting people to centre the mirror. In fact, if you do all of the other steps correctly and ignore this one then the step should take care of itself. Still, you can try to do it if you like. The problem comes if the secondary is too small. On some telescopes the secondary isn't big enough for all of the primary to seen at the same time. In this situation you will never be able to see all three mirror clips. With your eye at the focal plane and looking through the peep-hole you should be able to tell whether or not it is physically possible to see all of the primary. If the image of the primary in the secondary looks bigger than the secondary itself then you won't be able to complete this step. If that it is the case you should just ignore it.

You won't lose much light (it will be impossible to notice the difference) and the light you do lose will be from the mirror edge. On many mirrors the edge is the part that's the least good and so you might actually be getting a better view if the edge is not visible.

[TwistedJester]

Thanks. I think im gunna leave it as it is. Everything is fairly central. But when I look down the focus tube without any lens or collimator. Not all of the primarry mirror is visible is this correct?