The value of Good Collimation

[alan potts]

I was not sure where to post this but as it uses eyepiece I thought it would not hurt here, if any other Mods thing it would be better elsewhere please feel free to move it.

I used my LX 12inch scope last night which sits in the observatory on a rather large tripod that looks big enough to hold up the sky. I set is working with the laptop and as it is parked and almost finds things from the off so I though I would take a look at Mercury and very close by Mars, in the semi dark sky. As you would expect they didn't exactly set my pulse racing, loads of abberations from the atmosphere with both being so low. Turned to Sirius which is also lowish now and even that didn't sing the normal songs, even the Moon didn't really jump out at me.

I then notice a very slight comet like appearance as I brought Sirius to focus, this prompted me to look at the collimation, so I defocused the star, not the best to choose but I have done this before a few times so sort of know what I am up to. With the 31mm Nagler the magnification was about X 98.3225, I say this because with the SC type of scope the focal length changes so you never really know what the focal lenght is. Anyway at this power the de-focused Sirius lookd fine, a bit colourful but fine. So it was off to the house to bring some shorter eyepieces to whop up the voltage, a 6mm Delos should suffice I thought with an eye watering X508, I would never use this type of power on a target with this scope, maybe with any scope.

So I manged to get Sirius in the middle and sure enough the shadow of the secondary was slightly off centre and I do mean slightly, you would never notice using a lower power. So I tweaked 2 of the alen screws about a 1/20th of a turn it may have been less and now the shadow was absolutely in the middle. Put the 31mm Nagler back in the diagonal and my oh my what a difference, a tight and much smaller Sirius, I almost thought it was another star, much more controlled and showing lovely diffraction rings, that sort of woke me up everything had a snap about it.

This really brought it home to me just how complacency can find its way in even when you think you are on top of the game, on the whole though these scopes and Maksutovs do hold collimation well but it pays to check as I was about to blame the seeing. It was almost like I had a new scope and if you could only see the amount of adjustment I carried out you would never credit it and I am not totally sure I really believe it either..

Hope this helps someone a little

Alan

[John]

Good piece Alan

The SCT's I've owned were certainly capable of providing great views but the sharpness and contrast reduced markedly if the collimation was out even just a bit.

I'm sure you have seen this web page but it certainly made an impression on me in terms of illustrating the issue when I first came across it:

http://www.astrophoto.fr/collim.html

[alan potts]

John,

I had not seen that page and I have to say it is very good, at least I feel better after reading it because the amount of adjustment I made to the SC would in my books hardly account for the improvement. The slap around the face was though the realisation that I have become complacent, in some ways it was good to have a kick in the pants as it sort of put a new lease of life into the session.. I even found a mag 13.6 galaxy, sorry the goto found it .

Alan

[deepspacehunter]

Alan

 I realized the IMPORTANCE of PRECISE COLLIMATION several years ago...( although it took me years to realize it ) I was living in the country and I had a HARDIN OPTICAL 12" DOB... I tweaked the collimation via the STAR TEST METHOD and WOW...The view of the STAR FIELD was actually looking 3 Dimensional.... I had been observing with a C11.. and decided that I wanted to get a 12" DOBSONIAN again... I found a 12" CELESTRON STARHOPPER...it had some issues.. but the guy told me he would take $450 for it... I cleaned the mirror when I got it home ..( standard procedure when purchasing a used Reflector for me ) Anyway, when I took the mirror out ...it was actually in real good shape, then I noticed on the side of the mirror... it said ROYCE... I looked up ROYCE MIRRORS.. and Man, did I get lucky !!... I have since equipped it with some really fine Eyepieces and I get INCREDIBLE VIEWS through this Telescope... so now I am 58 years old and I FINALLY HAVE GOT IT RIGHT !!!   My ASTRONOMY HOBBY has never been more fun and rewarding ever in my life....CLEAR SKIES TO ALL...

Mark

[goodricke1]

Another +1 for collimation, took the plunge last night and was rewarded with stunning views of Izar - gold and blue/green pearls with clear black space intervening. Pulcherrima, the most beautiful, indeed.

[alan potts]

Goodricke 1,

I really think we can never over stress the importance of collimation being spot on.

Alan

[michael.h.f.wilkinson]

I should check my C8 next time. Got hopelessly bad resolution on the sun in white light (could also have been tube currents), although the last Jupiter shots i made where very sharp. Still pays to check

[alan potts]

Any time the scope temperature is at odds with the ambient it's always bad news, I used to get problems all the time but now it is outside it is one less thing to worry about, the sun does hit the roof of the obsey but a walnut tree offers shade long before I can use the scope most of the time.

Alan

[astromackem]

Goodricke 1,

I really think we can never over stress the importance of collimation being spot on.

Alan

If you zoom out on a star and you see the secondary mirror in the middle and the clips of the primary nice and symmetrical..is that enough?

[alan potts]

I am talking for SC scopes here they don't have clips that I know of, if you have a newtonian then it is a different process.

However on SC scopes,

It pays to do this but increase the magnification until it is fairly high. On the piece I posted at the top of the thread the set-up looked well enough on X74 and not even that bad at X90, but it was there I started to see a small failing, as said I made my adjustments at over X500, you really need only the tiniest tweak at that power and always re-centre the star after any movement.

Alan.