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Collimation Proving Difficult...

flapjackboy

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flapjackboy

flapjackboy

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After having a good look around last night my scope seems to be out of collimation (I did a star test and the image was 'skewed' to the left, i.e. there was more of an aura there...came I think its called?). Ive attempted collimation today but have run into a problem or two, even after reading the collimation guides on here. Ive moved the secondary mirror and adjusted the tilt, but the problem is the bottom right of the image has a black area which I cannot seem to get rid of. I've moved the image to there I think it should be, and would be able to see all the primary mirror clips, but the bottom right one is blocked by this black spot. Theres also a rectangular bit sticking out of it (its not my focuser), which I cannot identify. I havent touched the primary mirror adjustment screws so Im not sure if it could be something to do with that (I dont want to make it worse), but I cannot tell how to get rid of that black area. Any suggestions on what it could be and how to fix it would be massively appreciated! Thanks.

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flapjackboy

flapjackboy

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Cheers outlash :D After wtaching that video I had a fiddle and it turns out my secondary mirror has a little metal clip thats at the bottom, and thats what was showing. My secondary mirror was way off :lol: Its now in line but I had to move it so far toward the primary mirror the adjusting screws wouldnt reach...its much better than it was but I need to get some longer screws to adjust the mirror. Its progress though, thanks :D

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Black Shuck

Black Shuck

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Interesting that you've had to move the secondary so far that the adjusting screws aren't long enough though.

Got to say that doesn't sound right! The secondary will be a bit precarious at the limit of the screw thread. Stating the obvious but you really don't want it falling off! :shock:

I would be inclined to take it back a few turns and start from the begining again, if you can. The link that outlash sent is excellent, helped me no end when I was in a similar situation!!

Bill£

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flapjackboy

flapjackboy

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Righty...I had a fiddle and am still a tad unsure so Ive attempted to take some photos. The first is how it was aligned (as closely as possible) before I fiddled with it yesterday, and the second is how it was yesterday (i.e. the tilting screws only just reach). Not perfect I know but it seems to look more how it should. My photography isnt up to much...

Before

After

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Black Shuck

Black Shuck

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Allowing for the camera angle I don't think you're too far off. The advice I was given is that if you can see all three primary mirror clips in the collimation eyepiece then you are about there.

It is very difficult to explain but remember when you are adjusting the tilt of the 2ndary the three screws work against each other so you may need to loosen one before you tighten another. I found it handy to take a gentle hold of the post that the 2ndary is attached to (not the mirror itself) and apply light pressure (be very gentle) with my hand to see which way the mirror tilted when I moved it. This gave me an idea of which way it needed adjusting.

My scope handbook told me never to touch the centre screw but having seen the "andys shot glass" link that outlash posted earlier I definitely needed to adjust this (my scope was quite a way out when it arrived). This is the bit where you can drop the mirror so be careful.

Keep watching the video posted earlier (I needed to watch it many times), keep going back and take a look and take your time. It can be very frustrating at first - my first attempt took all afternoon!!! :shock:

Perhaps one of the more experienced SGL members will be able to explain better or have some more tips for you. Once you get the hang of it you will breeze through it.

Hope this helps.

Bill£ :D

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proflight2000

proflight2000

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Flap, from one very junior collimator to another, try what I did and just practise. Get the lid off an old film cannister and put a hole in it dead center so that you can see through it, does not need to be massive just a tiny hole. Put the cap into the eyepiece holder of your scope and look through it. Firstly, un tighten the center screw on your secondary mirror and jiggle it very nicely until you can see the 3 primary mirror clips, once you can see all 3 of them slightly re tighten the scondary mirrors center screw.

Whilst still looking through the end cap, use an allen key or whatever you need to turn the 3 tiny screws/grubs/allen key grubs and then center the middle part of the view, in effect you want to center everything. Once you are happy with all the centering, get your collimator out and put that in the eyepiece, line up the cross hairs so they are roughly on top of each other to some extent, then carry on adjusting the 3 little scres until it again is all centered.

One word of warning, if the secondary is unscrewed too much focus can be a problem, so it may be an idea to bring it all the way to the back again and then centering it using the cap. Its not brilliant I know but I have found that it is getting easier,today I made a point of knocking it all out of sync so I could play around getting things in place again, took me 10 minutes where before it took me hours.

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flapjackboy

flapjackboy

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Win! Thanks a million proflight and bill, Ive managed to get the secondary mirror as it should be now; Im not dure I would have done without your help. I was using a 35mm film cap, but a canister works better. Its taken me around 2 hours to get to where I am, but I can actually see the 3 clips now. I did move the secondary down a lot and had bought some long screws yesterday...I managed to get it all aligned a long way down the tube from where it was originally, but put the shorter screws back in and with the secondary at a different tilt it has the same effect. Just the primary mirror to go now :D Cheers.

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Kaptain Klevtsov

Kaptain Klevtsov

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but put the shorter screws back in and with the secondary at a different tilt it has the same effect. Just the primary mirror to go now :D Cheers.

No it absolutely doesn't have the same effect. A cone centred on the focus tube axis should just touch the edges of the secondary mirror, it must be in line with the focuser tube or the light will enter the eyepiece at an angle and it will be horrible.

Use the film canister with a hole in it by all means, but another way to do it (secondary in-out position) is to just look down the focuser tube. You need to make sure that you eye is central by viewing both sides of the tube and keeping the view the same, then move your head back and forth towards and away from the focuser. You should see the secondary mirror touch the edges of the focus tube evenly if its in the right spot.

Captain Chaos

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Black Shuck

Black Shuck

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Thanks CC, I knew one of the "big guns" would eventually come and help out. 8)

FJB, take on board CC's advice and keep watching that video clip - it's priceless!! If you are like me you will have a eureka moment when the realisation of what you are looking at hits you!!

It also helps if you are collimating the scope pointing toward something quite bright - i.e out the window or outside -taking due care with respect to the sun :sunny:. (My scope manual told me to point against a white wall (not good enough -IMO).

At the risk of making a complete a*se fool of myself see the image below, I believe this is correct - if it is wrong please can some one advise!!! :D

image.jpg

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flapjackboy

flapjackboy

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Thanks Bill & Chaos for your patience and input on this topic. Ive watched the video some more, and have re-done my collimation of the secondary mirror using the method captain chaos described. My collimation looks like bills only the spider vane is off (meaning I need the primary adjusting...I hope); as for the clips on the sides it looks the same. I'll leave the primary mirror adjustment for tomorrow in case I botch something tonight. Cheers.

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Astronut

Astronut

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Probably a bit late this but...

As excellent as that collimation video linked above is, this link might also prove useful.

http://www.backyardvoyager.com/CollimationFAQ.html

It's one of the most detailed tutorials I've seen so far on collimation.

You might want to have a look on this one too.

http://legault.club.fr/collim.html

This one concentrates on the final fine adjustments using a star test.

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flapjackboy

flapjackboy

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Awesome links Astronut, they provided a good read. Ive managed to get my primary alogned today, which thankfully went without a hitch. Everything seems to look as it is in Bill's photo, so im thinking its all correct. Thanks for helping me through it :D

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