Collimation Help

[Skiddins]

Hello all

Having had my Celestron 130 SLT less than a week my 18 month old niece has manged to pull the scope over and bang the end with the mirror, slightly denting the case (I was so gutted I nearly cried )

It now won't focus very well and certainly requires collimation.

What would be the best tool to get for this with my scope?

I have had a go using the eye through the focuser method and managed to improved it, but it's still nowhere near as good as it was.

I was looking at the Baader Laser Collimator, would this be suitable for my scope?

Any helpful hint's/tips to get it all sorted or should I leave it to someone who knows what they're doing?

Sorry my first post is a bit of a downer.

Just to show I have already had better times with it I took these using an iPhone held in cold shaky hands. In the eyepiece they were much sharper to the human eye.

Skiddins

[chemtom24]

you should be be able to collimate it pretty well yourself without using any 'tools'. a better way to do the eye-through-the-focusser trick is to get a cap to fit over the end of it, or paper, anythign that will block it, and put a pinhole right in the centre, then look through the pinhole to centre the mirrors.

if its badly out then it might take a while but theres plenty of collimating guides out there, this one has some good pics to help explain the process, what your are trying to achieve etc, and what it should look like when its done (last one was most important for me! )

How To Collimate a Newtonian Telescope - The Galactic Fool

a tip someone told me on a building site once which has stuck with me... dont be scared of it. ( we were concreting.. work that one out..) anyway, dont be afraid to make adjustments, youre not going to break the thing! and once you get it right, its a lovely feeling

[kniclander]

a cheshire collimator is better than a laser in that the laser might be inaccurate (uncollimated) and the laser (unless you use more complex methods) depends on the secondary being right to get the primary right. IMHO the best guides are Astrobaby's guide (on SGL) and Andy's shot glass (google). The latter is less thorough but maybe simpler.

[NGC 1502]

Good advice already given. The good news is that dents in the tube are only

cosmetic (unless really massive) and once collimated, your scope should work fine.

Best regards, Ed.

[Adamski]

Astrobabies is very helpful on collimating, using a plastic 35mm film case and some cardboard.This is the method I use and have had no problems at all. Sorry to hear about your unfortunate mishap.

[TheThing]

Without doubt, the easiest guide to collimating a scope is from Andy's Shot Glass and you don't even need any special equipment, just your eyes!

[Skiddins]

OK, after struggling a bit with the film cannister approach (probably down to my drilling) I decided to try the technical approach.

So I now own a Hotech SCA Laser Collimator.

It's main selling point is that the rubber rings around it can form a nice tight 'seal' inside the focuser so that you know it's dead central, great, except that the eyepieces are never quit central due to the thumb screws etc.

I therefore reduced the diammeter of the rubber rings until they were very close to the size of my eyepieces (measured with a vernier), then used the thumbscrews to hold it in place.

The secondary mirror was out of alignment so I tried to straighten that out first. The only problem being that my primary mirror doesn't have a 'doughnut' in the centre so I had to judge it by eye.

I then adjusted the primary, then tested using an eyepiece, then adjusted again. I repeated this a few times until I seemed to be getting consistent results.

Does anyone have any recommendations for how to ensure the secondary mirror is properly aligned?

Thanks

Skiddins

[Skiddins]

I'm still having huge problems with this

I bought a Cheshire eyepiece so I could try to line up the secondary.

After a lot of fiddling I manged to get the secondary mirror to be an almost perfect circle just slightly smaller than the end of the cheshire.

When I try the Hotech in it I notice that the laser is nowhere near central on the primary. If I adjust the secondary so that the laser dot is as central as I can judge it to be (there is no 'doughnut' or mark on the centre of the primary) the secondary is not a perfect circle and subsequently doesn't appear to be quite properly aligned.

Ironically, I started messing with the secondary due to all the pictures I've seen etc the secondary looks dead central and the Cheshire reflection is also dead central, later I found that on fast Newtonians (F5) the cheshire reflection is always slightly off, so nothing on the secondary probably needed doing at all.

As far as I can tell the focuser is dead straight (when I look along the outside of the OTA at a shallow angle I can't see any distortion in the relections around the focuser and I have also tightened up the rack and pinion system so there is virtually no play in it.

I think I may have overtightened the screws slightly that hold the primary in it's cell but this is easily solved.

Although this image is from another site it shows roughly what I see from a de-focused star. Note, my off centre secondary switches from top to bottom depending on whether I'm intra-focus or extra-focus and the outer circle of light is not round, more of an ellipse.

Does anyone have any other idea's

[Adamski]

Honestly mate, if you print off astrobabies guide you won't have to buy anything and it will show you how to set your secondary mirror, with the film case and a peice of card to block the reflection from the primary. Takes about 15-20 minutes, once this is done you move on to the primary which is a bit quicker. After the secondary mirror is set you won't need to do it again very often and the primary will just need tweaking from time to time. You can do it indoors or out but be careful not to drop any tools down the ota. A small cross head screwdriver and small allen key are the only other tools you will need. Good luck.

[franco]

another "big up" to astro babys guide!

my first time collimating and had no idea what i was doing, its very fiddly and i dis throw one or two toys out the pram while trying but managed to align everything up in the end.

"stay calm and carry on"

[damnut]

Hi There,

I had similar issues with an 8" newt, took to local astro shop RVO, left it there, they collimated it £10.

It may be woth finding a local dealer who will put it back a 100% and then when it goes slightly akilter with use diy!.

Good Luck

Damian

[faskunji]

I lost allen key for my Celestron Nexstar 130 SLT.
Can you tell me if it is really 6 sided allen key or 4 sided robertson key? I do not remember.
And also please give the key size so I will try to buy it.

Thanks

[freewheeler]

I would just like to give a word of warning based on personal experience when using a laser. When it shines down the eyepiece it is deflected by the secondary to the primary and back to the secondary. The laser beam never escaping from the telescope. As a newbie doing my first collimation, not knowing which way to turn the adjusting screws etc. I made things worse before I made them better. In fact, at one stage, the return journey of the laser beam missed the secondary mirror completely and escaped from the end of the telescope. In this event the laser would shine right into the eyes of the person peering in the open end trying to collimate the scope. Fortunately I had read all about this possibility and always held a piece of paper near to the end of the scope to check that there was not a tell tale red dot hitting the paper. I did this after every adjusment and in my case it was a good job I did.

[freewheeler]

Deleted due to duplication

[Dave In Vermont]

9 hours ago, faskunji said:

I lost allen key for my Celestron Nexstar 130 SLT.
Can you tell me if it is really 6 sided allen key or 4 sided robertson key? I do not remember.
And also please give the key size so I will try to buy it.

Thanks

I don't have the Celestron, but they are made by Synta in Taiwan, China. As such their dimensions are quite likely the same in the many brand-names these telescopes are sold under: Celestron, Skywatcher, Orion-USA - maybe others? Don't know. But the usual dimensions of the secondary-mirror are their collimation-bolts are 2mm or 2.5mm and they are hexagonal Allen-Bolts. Allen-wrenches can be found in a set with 2mm through 6mm or so, and are less expensive bought as a set rather than one-at-a-time.

A warning for you and others: Work with the telescope either level, or the front-end slanted downwards. This way when you drop the wrench, it won't hit the optics on it's way down.

Take your time,

Dave

[freewheeler]

16 hours ago, faskunji said:

I lost allen key for my Celestron Nexstar 130 SLT.
Can you tell me if it is really 6 sided allen key or 4 sided robertson key? I do not remember.
And also please give the key size so I will try to buy it.

Thanks

I have a Celestron Astromaster 114 and it uses a totally standard 3 mm 6 sided allen key, a very commons size available as part of sets from DIY stores. The first thing I did was grind off the short leg, grind the end of the long leg to a point and hammer it into a small rat tail file handle. It made it so much easier to use. Of course I was just being a cheapskate as you can buy single allen keys set into a tee handle.

[Dave In Vermont]

3mm? That's news! Thank you!

Seems Celestron likes to be unique. I'll toss that in my stacks.

Happy collimating,

Dave