Collimation for a newby

[Legin (Nigel)]

Thanks for the tips

Collimation is slowly making sense now. Heck I can almost do it right. I have got my scope pretty well collimated now. The secondary mirror seems a bit out of whack though.

I think the tilt of my secondary mirror is a bit out. I go through the steps of collimation aliging the secondary mirror to the focus tube (I am pretty sure that is right). Adjusting the tilt of the secondary mirror is tricky though. I never seem to be at a point where I can see the whole primary mirror. I can almsot see all of it at times but I just seem to miss a slightest bit of one edge at most times (if that makes sense).

I have tried racking the focuser in and out to help see all the primary mirror however the most I seem to see is about 98% of the primary mirror.

Hmmm maybe I just need to fiddle around a bit. Hmmm do you think the mirror could be out of alignment with the focuser after all. I swear it looks circular and I can see the whole mirror when I go through the first steps of collimation (aligining the secondary mirror). But I am a bit unsure of myself in any case. I mean, I look through the focuser and see a nice round, centered primary so it should be ok, right?

Arrrghh, maybe I just need more practise...

I am getting better at collimation. At least now I am starting to make more sense of it all. I can not wait to get the collimation right. The views with a slightly out of whack scope are pretty GOOD so I can imagine when I get it collimated it will be awesome.

Jupiter looks pretty darn good this month. Not to mention the Moon, oh and those stars over there, and there, and there and...

[Kevnool (Kev)]

Thats good news there legin i,m glad its all coming together stick with it mate, when you get it right you,ll be glad that the money you spent yesterday is giving you the image you deserve today......cheers Kev.

[Starkler (Geoff)]

Nigel it helps to have a bit of an understanding of what alignment steps are the more critical ones.

Errors in centering the secondary under the focuser will result in uneven edge illumination at the focal place. Not critical and you may not notice any roll off in brightness at the edges.

Error in centering sight tube cross hairs over primary centre spot (secondary tilt and aiming). This results in a tilted focal plane at the eyepiece. Small errors within a few mm are ok.

Error in aligning primary centre spot to illuminated cheshire ring. This is the one you want to get as close as possible for good results.

For astrophotography all of the tolerances become a lot tighter for best results.

[Legin (Nigel)]

Ok things seem almost right now.

I have the collimation pretty good except the little ring on the primary mirror seems a bit off center. When I look through the commlimation tool I can see the three bits that hold the primary mirror on the very edge of the view. I can see the black circle and I get the little dot to line up perfectly. Except the little center cirlce and the black dot seema bit off center. Only a little off center but non the less off center.

If I get the center

The three bits holding the primary mirror to all appear at once. The best I can get is two and one barely off to the side I can barely see the edge of it (so I guess I see all three at once).

[multiweb (Marc)]

Bit of reading that may help.
http://www.skyandtelescope.com/howto/diy/3306876.html

[IanL]

It a long journey but something that everybody probably has to master.
I found it hard collimation a Dall Kirkham system and still working on it at the moment.
One thing really helped me to get a picture in my mind’s eye was to label with masking tape A, B, C on the tube where the screws are
So that when I looked at the image I could see what screws I needed to turn. Now I am going down the road of artificial star DIY.
The journey for me continues. Sometimes I feel like smashing the scope to buggery but its times like that you need a break.

Ian

[doug_parkes]

hi Nigel,

be wary when using a laser collimator. Most of them come out of their boxes poorly aligned to begin with! They need to be spun in a lathe chuck or somesuch and the beam alignment checked. If you cannot get that done then rotate the laser collimator while it is in the focuser tube and watch the projected beam to ensure that it is spinning in a tiny circle and not in a huge arc!

What suburb do you live in? You would be well advised to join an astronomy group and have someone with collimating experience guide you through the procedure.

Doug

[Jen]

Originally Posted by Kevnool

I hope Jen you watched the process and now your a champion collimator is it gunna be a call out again ( is that the same fella that lives 8 minues out of town on 60 acres of river front as i have read in another thread who offered accomodation for knowledge ?........cheers Kev.

Yep thats him
He has a very nice scope
but with all this yucky weather i still havnt had a chance to have a play with it
Yep a star party in swan hill would be great

[ColHut (Colin)]

Dear All,
I follow Don's article and the various instructions and tutorials. I use a combination Cheshire (an Orion). Unfortunately, being very short-sighted I find it hard to accurately align the secondary to centre the primary in the Cheshire and harder still to accurately align the primary as I cannot get good eye placement because of the glasses.

Any ideas? I am thinking of going to a barlowed laser for the alignment of the primary - will this help?

cheers

[Legin (Nigel)]

Ok I have improved the view significantly. The scope was pretty badly mis-collimated when I used it for the first time. All the stars looked like little comets. I seem to have made the view a bit better now but it is still a bit out of whack.

The most trouble I am having seems to be aligning the secondary mirror.

I have abit of a question about aligning the secondary mirror under the focuser. The way I am trying to do it is simple. I place a peice of cardboard or paper in front of the primary mirror. This way all I can see through the focuser is the secondary mirror. Then I use my sight tube to try and center the primary mirror.

However this brings a few problems. One it is extremely dark and I can hardly see anything and secondly when I loosen the center screw (the one you need a screwdriver for) the whole mirror seems very loose.

Hmmm. Any advice here would be appreciated. I know collimation is more practice makes perfect but it just seems a bit too tricky for me at the moments.

LOL though I did improve things over all I have to admit I really mucked my collimation up severely the first few tries . Boy oh boy I am glad I got things back to nearly perfect again. Oh well I will get sharp view one day

Oh and what about barlowing my laser? Will this help. I have heard this helps a fair bit. Heck it will probably cost me a few bucks for a barlow lens but it is worth it if I obtain avery accurate collimation tool.

[erick (Eric)]

Originally Posted by Legin

However this brings a few problems. One it is extremely dark and I can hardly see anything and secondly when I loosen the center screw (the one you need a screwdriver for) the whole mirror seems very loose.

Shine a light on the subject?

If the mechanism is like the GSOs, the three collimating screws play an important role in supporting the secondary mirror firmly in place. If you adjust the central screw such that the mirror moves away from the three collimating screws, yes it will get "floppy". You need to screw the three collimating screws in to meet the mirror holder again. The opposite - if you have to adjust the central screw to move the secondary away from the primary, you'll need to back off the three collimating screws so the secondary can move in that direction. Reach in and hold the secondary holder and adjust central screw until it is well located under the focusser, then screw the collimating screws back to meet the mirror. Then check secondary position again and adjust. Keep iterating smaller and smaller moves each time. After that, away you go adjusting the tilt of the secondary.

Another thought is that there should be a firm spring around the secondary central screw pushing the miror holder away from the spider. Is it missing? Is it really too weak? Replace it with something the right length that is firmer. Bunnings have a selection of springs - it's the compression springs you want.

Originally Posted by Legin

Oh and what about barlowing my laser? Will this help. I have heard this helps a fair bit. Heck it will probably cost me a few bucks for a barlow lens but it is worth it if I obtain avery accurate collimation tool.

Well a barlow is a useful device to have, anyway. The GSO 2" 2x ED is quite economical and will be useful with your eyepieces to obtain a greater range of magnification (and a few other benefits, but let's not start an argument about eye relief here!).

With respect to a barlowed laser for collimation, my understanding is that the physics of the barlow lens removes a key error inherent in using the laser. I just pop my regular laser in a barlow (either the 2x one above or even a Televue 3x) after I think everything is well lined up (after regular laser and cheshire), then I have a piece of white card through which I have punched a regular hole punch hole. I reach the card into the tube between the focusser and the secondary and allow the laser to pass through the hole. Invariably, the shadow of the ring on the primary is smack bang centred on the laser beam.

A bit of a fancy approach, but here is an article that will help you with the concept of a barlowed laser. (Note Scott has a laser with barlow built in).
http://www.iceinspace.com.au/index.p...63,406,0,0,1,0

[Legin (Nigel)]

I think there is a spring inside around the large central screw on the secondary mirror. I have attached a picture so you can get an idea what it looks like. It feels springy and if I turn it with my hand I can definately feel something springing around in there. At first that springing kind of scared me and I thought I damaged something but it seems normal now that I know what is going on.

Hmmm this is slowly making more and more sense to me each time I have a go at it. If nothing else I have learned a fair bit about how a Newtonian telsecope works.

In any case my secondary mirror seems to be the main problem. Aligning the secondary mirror actually seems quite easy. The secondary one is tricky to say the least. But alas I will not give up on this as I think this scope will be quite nice when it is collimated.

The scope itself is a Omni XLT 150, FL=750mm and a 150mm diameter so I figure that makes a F/5 scope. Unfortunately this means collimation becomes more critical for perfect viewing (or at least near perfect). Hmmm I am getting the impression that newbies should start with refractors (joking).

Anyway I will poke around with it again over the next few days and see what I can do. Eventually I want to take some snap shots of the planets, moon and maybe a few night sky objects. Though photography is not my primary objective with this scope I will be happy for a nice crisp view and at least ok'ish pictures.

[erick (Eric)]

Yes, Nigel - pretty standard looking chinese secondary mirror mechanism.

Here's what I did to replace the three collimation screws without buying Bob's knobs:-

"Lastly, finished off my knobs for the secondary mirror tilt. I'd grown sick of the Philips head screws, so found some long M4 bolts (cabinet handle fittings are M4), found some of the wooden plugs that fit into screw holes on furniture, drilled through these, added a few nuts and washers and I had Eric's Knobs. Only trouble, they very slightly protruded into the light path, so I filed flutes into the wood to significantly reduce this, with the added advantage of increasing the grip, gave them a paint and reinstalled and rechecked and reset collimation."

Let me know if you want a photo.

You said :- "If nothing else I have learned a fair bit about how a Newtonian telsecope works." Hurray! Once you know how things work, you are so much closer to 1) getting the best out of them, and 2) improving them.

[erick (Eric)]

Originally Posted by Legin

Hmmm I am getting the impression that newbies should start with refractors (joking).

Wash your mouth out with soap!

[Starkler (Geoff)]

Do be careful that when playing around with the secondary that you dont over tighten the screws trying to nudge that last little alignment tweak.

Its easy to damage a lot of secondary holders this way creating divots formed at the end of the screw where it bears on the secondary holder.
Once these divots form, fine tuning alignment can be a PITA as the screw ends will always want to fall into these divots.

[erick (Eric)]

Hence the work I did when I had the holder apart recently to install the dew heater:-

"While waiting, took the opportunity to do some work on the mechanicals. Took any sharp edges off the end of the central mounting screw since it may screw through the holder into the cotton wool packing. Stretched the spring a little to give a bit more rigidity. I noticed that the three collimating screws had been chewing into the washer. One at a time, I removed and cleaned up the ends of the screws, finally with some fine emery paper until they were silky smooth. Filed down and used emery paper on the washer to get some removal of the deep gouges, and decided to fix it to the end of the secondary holder with a few spots of silicon. Firstly to stop it falling off when removing the secondary holder. Secondly to make the three collimating screw ends contact clean metal away from the early marks which covered much of the surface at the radius of contact."

Take the screws out one at a time and file the end to remove any sharp edges, then emery paper it until smooth and flat, then replace, the remove the second etc.

[ColHut (Colin)]

Originally Posted by ColHut

Dear All,
I follow Don's article and the various instructions and tutorials. I use a combination Cheshire (an Orion). Unfortunately, being very short-sighted I find it hard to accurately align the secondary to centre the primary in the Cheshire and harder still to accurately align the primary as I cannot get good eye placement because of the glasses.

Any ideas? I am thinking of going to a barlowed laser for the alignment of the primary - will this help?

cheers

Bump

[TrevorW]

This link may help

http://www.skyandtelescope.com/howto/diy/3306876.html

Cheers

[Legin (Nigel)]

Hmmm I have my collimation pretty nice now. I guess. The stars look like little pinpircks but some little tails remain though it is minimal now. My main problem seems to be the fact that I can not see all of the primary mirror.

I will explain and maybe it will make sense. I align the secondary mirror under the focus tube to a point where it slooks pretty aligned. Then I try to adjust the tilt. I rack the focus tube in and out and in and out. I twist crews and whatever. I can see the three holders on my mirror but I can not seem to see all three at once. The best I can see is two and the third being right on the edge of the view (I mean needle fine on the edge).

Still I have improved my collimation a fair bit. When I first unpacked my scope the view was a little less than spectactular. The stars have less tails now and the Moon looks crisp and awesome. Heck I can even begin to see details on Jupiter, which is fast becoming my favourite thing to look at.

I really think this little scope, though it isn't the worlds best, can be significantly better.

Any ideas on this one I will try to get a picture of what I see through the sight tube. Though getting a picture of it is difficult to say the least .

What are your views of the Celestron Omni XLT 150? Is it a good or bad scope? I purchased it because it was cheap and on special. Though I am starting to think I would have been better off spending a few hundred more on a better scope. Oh well there is always my next scope eh?

[Legin (Nigel)]

Oh wow...

Ok today I got a bit adventurous. I pulled out my laser collimation tool. Then I racked the focus tube as far in to the scope as it could go I put the laser tool in and made certian it fit without being loose.

Then I looked at the spot on the primary mirror. Ewwww the red laser dot was half way to the side of the mirror. Not even close. Ok so I fiddled around adjusting the tilt of the secondary mirror. Eventually I got the red dot centered.

Then I aligned the primary mirror using the laser tool.

I then checked the red dot again and repeated the steps about three times.

Eventually everything lined up nicely. So I put the laser tool away and check with my sight tube. Usually when I do this everything looks lined up with the laser but isn't lined up in the sight tube. Holy starlight Batman the sight tube showed everything aligned.

The alignment was not 100% perfect but it was pretty darn close to it. Everything lined up both in the laser and the sight tube. I was happy to say the least. I still need some fine tuning but everything looked pretty darn good so far.

I waited until dark and went out to look at Alpha Centauri and other things :p ... The stars were little pin pricks of light with bare minimal, if any, flaring. This was using the standard eyepiece that came witht he scope (not the best eyepiece around I might add but it is good enough). Yep stars were sharp as they could be. I had a bit of a problem losing some focus near the edges of the view but I messed about witht he screws holding the eyepiece in the focus tube and it seemed to fix the problem.

After a while I turned the scope to the Moon. I was amased. The first thing that struck me was how much brighter the view seemed to be than I had on other nights. The moon was so bright I nearly had to squint to see it. It was blazing and sharp. The craters all were sharp and crisp and far more detail than ever before. I noticed all manner of things I couldn't see before. I was very impressed. The birghtness was markedly different to the badly collimated views I had before. Everything just looked sharper.

So I tried my 3.5mm Hyperion eyepiece (a nice eyepiece by the way *oh boy* it is nice :p). I saw so much detail I hadn't seen on other nights. The seeing conditions were not the best as the view was swimming around a bit but with such high magnification on this tiny scope I was not complaining. In the few moments where the air cleared enough to allow a crisper view I could see craters within craters and rills and mountains and valleys and ... and .. and.........

Anyway lets just say I am holy doollllly shell shocked at the level of improvement. The views now are like a whole new scope compared to the days when it was way out of whack.

I have the scope outside now cooling down. I am hoping to catch Jupiter when it gets high in the sky and where I can see it from my balcony. Yeah I live in a unit so I need to move around to get clear views or wait for certian times for things to move into view. Jupiter is going to look awesome I know it .


So all my trials with collimation are starting to pay off. I knew it would be worth getting right and it was. I think I can tweak it just a bit more but so far it looks "PRETTY COOOOOL".