Collimation

[jdg600]

I have just got my new Skyliner 200p and, in the absence of anything to look at with it, have been fiddling with the collimation. I have made a collimating cap from a 35mm film canister but am a little confused about what I'm looking for to get the collimation right.

When I put the cap in the eyepiece holder and look through it I can see all three clips on the reflected image of the primary (hough one clip is slighty less prominent than the other two) so I'm hoping this means that the secondary mirror position is OK (or within tolerance anyway) and I don't need to mess with it. I can also see the outline of the secondary mirror (which appears slightly oval), the reflection of the eyepiece in the secondary and the reflection of the center spot on the primary in the secondary and I'm not sure which of these three things I'm supposed to centre in my field of view. For now I have centered the spot on the primary as best I can, is this right?

Also I'm not sure how much to tighten the locking screws on the primary. I found that they were only just finger tight as it came from the factory, is this how they should be?

Any help or advice would be much appreciated.

John

[James Albinson]

To answer the last question first, the primary retaining screws should just NOT touch the mirror - if you can squeeze a playing card through the gap between one screw and the mirror when the other two screws contact the mirror, this is about right. The main thing is that the mirror NOT be squeezed, but rest on two of the sideways supports. Mirrors are very sensitive to sideways pressure... The topple stop clips above the mirror should likewise NOT actually contact the mirror, but be just above it. Their function is to stop the mirror falling out of the cell, not hold it down. The mirror should rest on the back supports. The idea is that the telescope should go beyond the horizontal. Not intentionally!!!

As to collimation, have a good google around the web - I am sure there are reasonable instructions around - I will get back here if I find good ones. I have a set of Tectron tubes/collimators - old style, and they were worth every penny. They had instructions so I didn't bother web searching... Basically though, everything has to line up centered in everything else. This will be a good start and you can enjoy using the scope while you gain experience. More later if I can find it...

Regards, James Albinson, Support Group Keele University Observatory.

[jimmyjamjoejoe]

Astro Babys Guide to Collimation

That seems to be the collimation bible, i see it posted here every day. It doesn't seem to give instructions on solely using a collimation cap, but it gives some decent idea of what you should expect to see.

[MorningMajor]

That seems to be the collimation bible, i see it posted here every day. It doesn't seem to give instructions on solely using a collimation cap, but it gives some decent idea of what you should expect to see.

Astrobabys site is great and in conjunction with - you can't really go wrong!

Good luck

[umadog]

You're going to need more than a "cap with a hole". That won't be enough to get you accurately collimated, although it will work better than a slap in the face. Typically people use a Cheshire/sight-tube combination tool. Here are good instructions for using one: John Reed Home Page Collimation - Cheshire

[jdg600]

Thanks for all the advice. Astro baby's guide seems particularly informative. Will order a cheshire eyepiece and try again.

John

[LukeSkywatcher]

The main thing to keep in mind is not to be afraid of collimation. If you go into it afraid then you are likely to mess up and never do it again. Its just simply aligning the mirrors.

A cheap home made cap with a hole in it will get you about 95-97% of the way which is fine for most people who do only visual observing. For imaging, you really want it to be 100% on the dot (pun intended).

Also................larger scopes will need it done more often then smaller scopes,especially if your scope is being moved around a lot over any sort of distance.