Collimation

[meddyliol]

As my 15cm Sky Scan has not been used for a number of years, I am in the process of getting it ready for use again. I keep reading about  collimation (as if I don't have enough to worry about). I can assume that mine definitely needs some adjustment. I see that I can get a tool for the purpose which presumably negates having to cart it outside. What is a decent, reasonably priced, tool that might be recommended?

Cheers

Brian

[lonick]

Here you go;

http://www.firstlightoptics.com/other-collimation-tools/cheshire-collimating-eyepiece.html

[ronl]

I take it it's a Newtonian, scope, if so this guide will show you how,

and what you need. http://www.astro-baby.com/collimation/astro%20babys%20collimation%20guide.htm

[wookie1965]

Here is another guide i used inconjuction with the very good astobabys helped me enormously

http://www.schlatter.org/Dad/Astronomy/collimate.htm

[meddyliol]

I take it it's a Newtonian, scope, if so this guide will show you how,

and what you need. http://www.astro-baby.com/collimation/astro%20babys%20collimation%20guide.htm

My God, if that is a simple guide is I would hate to see a difficult one. Thanks for the info though. I think I will stick to photography.

Cheers

Brian

[RichM63]

Brian don't be frightened about collimation of a Newtonian telescope, it really is quite simple once you bite the bullet and have a go.

Follow all the steps in sequence, don't miss any out and you will get there.

Then in the future it will only take you 5 minutes if that.

All you are doing is aligning the secondary mirror with the primary main mirror so that the image being fired out of the focuser is aligned before it then goes through the eye piece into your eye, or if no eye piece then camera.

In other words 'unsquiffed light beams' for " Happiness is a Telescope called Collimated ".

[Charic]

meddyliol........before you buy anything, try this first!

Focus on a bright Star. Polaris is a good bet, as it wont drift across your field of view. Use a high powered eyepiece ( one with a low number on the eyepiece ) then de-focus the star one way or another either side of the correct focus. You should now  become aware of, and see something called the Airy disk? If this looks perfectly centred, ie the bit in the middle is centered, and all the rings that surround the centre appear to be concentric, equally spaced,  then no collimation is required (yet!).

Tools or not, this would be the final test/check of a collimated telescope. If the circles are good, leave well alone. If their deformed by some margin, then you need to learn about collimation. The disk looks like this, but google for more info.  https://www.astronomics.com/airy-disk_t.aspx

[Dave In Vermont]

Like so many before you, the piles of conflicting written How-To guides to collimation are quite often written by PhD physics professors, and that's very scary! I am here to tell you that collimation is really quite simple - once you get good information, and do learn the ONE cardinal-rule: Keep the scope's OTA - the scope tube - horizontal, or angled downwards a bit. This way if you drop the little screwdriver or Allen-wrench, it won't fall down the inside-tube and hit your primary mirror. With that said, you can do no harm to the scope by learning to collimate it. It's very forgiving. I promise.

So just relax and proceed slowly. If you get frustrated, or tired, go do something else for awhile. It will wait for you. Few, if any, telescopes have walked away in disgust. My one rant is that super-smart people write How-To guides for this, and they know how to do this blindfolded, but they are lousy at communicating/teaching using the written word. This goes a ways to explain why there are no less than 3 threads on this subject in these forums as I write this missive. And here's another good set of instructions:

http://www.backyardastronomy.com/Backyard_Astronomy/Downloads_files/Appendix%20B-Collimation.pdf

The guide from Astro-Baby is quite good. And do get a Cheshire/Sighting-Tube as shown in the link above. The first one is perfect, and the price is low. This one here:

http://www.firstlightoptics.com/other-collimation-tools/cheshire-collimating-eyepiece.html

You can also use a specialised laser for this, but I'll save that for a later date. Do come back and ask any further questions you may have. Or to announce your impending victory.

You'll Do Fine,

Dave

[Digger1895]

My God, if that is a simple guide is I would hate to see a difficult one. Thanks for the info though. I think I will stick to photography.

Cheers

Brian

Lol, it's really not that hard Brian. It does seem complicated to read but when you have the scope in front of you and can identify the different parts and see how they work together things will start to click into place. I can be very 'crack' handed and if you're anything like me once you have done it once you will think to yourself "is THAT it?"

[Digger1895]

*'cack' handed not crack

[meddyliol]

Thanks to everyone. I have ordered a Cheshire Collimating Eyepiece so will have a go when it comes, I was going to get a laser one but decided, after some research, not to. I haven't looked at the main mirror yet so don't know if the centre is marked. If it isn't, is it OK to take it out and put a mark in the centre? Or will that [removed word] things up even more?

Thanks again, I will try and digest everything that has been posted and will let you know how I get on.

Brian   

[meddyliol]

P.S. That Backyards guide looks useful  

[meddyliol]

P.P.P.S ? I just looked at the main mirror and it has a small circle in the centre.    

[Charic]

.........which reminds me, I need to re-apply my centre spot?

Took less than three minutes completed. And because I only removed the 6 cell retaining screws, and pre-marked the fitting, I still expect my collimaton to be good. Star test will confirm. I notice the new hole reinforcement sticker is much bigger than the original spot! The original spot just about fits inside the newer spot. There was still some of the spot left after the last 'test wash'. The new sticker is mounted on the originl, a quick blast with my Giottos Rocket, looks brand new.

[meddyliol]

Well, I have my Cheshire Collimating Eyepiece. The very, very rough sketch shown and the pic of the end of my 'scope are shown. I am not quite sure what to adjust. I am hoping that the primary mirror does not need adjustment but I suspect that it does.

Cheers

Brian

[meddyliol]

I have been adjusting the three 2.5mm allen screws and have got it better now. The mirror end has three philips screws and three allen screws. What do I do to adjust the primary mirror? I feel that I am getting there but do not want to mess about with the main mirror until I know what I am doing. What is the philips screw for in the centre of my pic?

Thanks for your help so far

Brian

[AndyWB]

The Primary mirror is the EASY big. I find getting the secondary right is the hard part.

The 6 screws should be 3 for adjusting it, and 3 as locking screws to hold the mirror in place once adjusted. I think. I'm not sure which is which, though.

The screw in the middle of the second picture is the one that hold the secondary mirror on. Think of it as a stalk, with the other 3 pushing the back of the secondary mirror mount to change it's tilt. This image should give you an idea of the overall structure, though on yours the head of the allen screw in the middle would be on the left - it's the philips one in the picture above - and that way round makes more sense to me...

But you get the idea about how it adjusts tilt. You can adjust the middle screw too, if you need to move the secondary towards or away from the primary mirror (to center it under the focusser) - but I'd loosen the other screws first, and make sure the scope is pointed down so that if you accidentally unscrew the secondary mount entirely it won't drop onto the primary mirror.

Good choice on the Cheshire over the laser.

[meddyliol]

Just about everywhere I read it mentions seeing the three primary clips. I can only see one. Is there a reason for this?

[buzzlightyear]

Try a star test mate its quick and simple, you obviously need clear skies though and north star is a good choice to test on.

[meddyliol]

Has anyone seen this video? Looks really good to me.

http://www.andysshotglass.com/Collimating.html

[Charic]

The video is ok. I wouldn't hold the edge of the secondary mirror whilst making adjustments, because there is the chance of touching the face of the mirror with your finger tips (the narrator mentions this) You only need to support the mirror by holding the mirrors stalk/holder.

A laser collimation tool by definition is accurate and reliable, but dont fully rely on your laser for initial setup of the secondary, unless the laser itself is  fully collimated, and has a perfect repetitive fitting when placed in the focuser. Lasers are ok if this standard is achieved. However a  laser, used with a Barlow for final adjustment of the primary mirror, doesn't really matter how loose the laser is, as long as it fits. Check out how to laser-Barlow  a telescope.

The Cheshire tool you have purchased will allow you to centre align the secondary mirror, and align the primary. Follow up your collimation procedures with a Star test to confirm true and proper alignment.

Have fun.

[Dave In Vermont]

I've found that keeping the laser flush with the end of the draw-tube - by holding it down by hand - and then rotating it works best. As for the Cheshire, I use both a laser and the Cheshire/Sight-Tube. When the two are in perfect agreement, then I go for the star-test. Works for me!

Happy Collimating,

Dave