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Quite worried about my first collimation..


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Hi everyone,

My viewing has finally got quite bad so it's definitely time collimate. I've been putting it off for ages, and have read some guides, but am just a bit concerned about totally wrecking it without someone to help me!

Plus theres the fact it'll be pitch black when I attempt it..

I don't have a collimation tool at the moment but use a bottle cap with a tiny hole made in the centre, I think it works okay...Should that do? Also, where should I start? I have never moved the primary mirror but I have adjusted the secondary, which do you think I should start with?

I realise it's quite a simple process but am still a bit worried about it!

Thanks :D

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Go for a laser collimator if you can. It took me 45 minutes on the first go, due to being completely inexperienced and ultra careful, thinking it was complex. It isn't and now it takes less than 2 minutes. Once you've done it, you'll wonder what the fuss was about. It really is straightforward with a laser collimator.

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what scope do you have?

the speed (f5 is fast and f11 is slow) to some extent dictates how accurate you need to be; it's more important with faster scopes than slower scopes to get the collimation spot on.

as others have said, it's really straight forward and once you have done it a few times it's a doddle.

the only way you can cause irrepreable damage is by dropping the secondary onto the primary but if you follow the rules (eg tube not vertical) then you'll be fine.

I have tried barlowed lasers, 'proper' cheshires and also a cheapo collimator which came free with a previous scope; I genuinely prefer the latter along with a home made collimation cap. my scopes have a long focal length (both 1.6m) and I find it easy to just move back and forth to check how the image moves when I make the adjustments.

read the suggested guides and this one Collimating a Newtonian and you'll understand it.

if you let us know where you are, there may be a kind soul near you to help and why do it in the dark? it can be done inside.

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Which scope do you have? Can it be easily removed from the mount? If so then i would suggest laying it on a table, with a couple of blocks to stop it rolling off! and then following the instructions mentioned above. Take your time and do things logically. If both you and the scope are in the warm and you cannot drop things onto the mirrors most of the worries have been eliminated - you will soon get the idea of what to do. After a couple of goes the whole thing will become second nature and you will be able to work outside with the scope on its mount.

Edited by Bizibilder
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It really is straightforward with a laser collimator.

A bit too simple sometimes. First of all, you're never going to evaluate the placement and rotation of your secondary that way, and I've seen people with obvious problems when they tried to compensate a 30° (!) rotational error with the laser collimator and the usual tilt screws ("I've run out of thread on those screws!").

Secondly, these are sometimes miscollimated or don't fit well in the focuser.

Thirdly, the return beam is an easy reference but not a very precise one.

So it's fair to say that cheap laser collimators are often deceptively simple. Though of course you can still get away with it on most slow scopes (e.g. f/8), as the collimation tolerances there are quite lax.

Edited by sixela
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Usual health warning that I have to give with this video: it gives the impression that everything will be concentric but that's not true, especially on fast scopes.

Ignore spider vanes and ignore the fact that the silhouette of the secondary you see in the primary is offset away from the front of the scope: that's actually correct and the video is not! Trying to "fix" this has driven many people to the brink of despair.

The following is normal:

Collimationyellow.png

Edited by sixela
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My advice for the original poster?

Given you have only a collimation cap:

-Don't touch that secondary! you have no tool for tweaking it yet, so just assume it's OK.

-Insert the collimation cap, preferably close to the focal plane (if you put a piece of paper in front of the focuser and then point your scope to the moon, that's where the moon's image is in focus. And congratulations on your first prime focus astrophotograph, albeit a fairly volatile one :D ). If there's no moon, rack the focuser in roughly like you do when you focus your 25mm Plössl and look at stars.

-Tweak the tilt of the primary until the collimation cap pupil reflection (i.e. the reflection of the round peephole you're looking through) is exactly in the middle of the doughnut of the centre spot.

-Done!

It's only a third of the whole collimation routine, but it is both the most simple step and the most important!

Edited by sixela
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Plus theres the fact it'll be pitch black when I attempt it..

I realise it's quite a simple process but am still a bit worried about it!

Thanks :D

one simple piece of advice......DONT!!!!! attempt in the dark make life easy and do it in daylight until you feel more at ease with the process:D

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I agree with gedmac. DONT attempt it in the dark. Once you have collimated the scope..........it will be a breeze every time. Its just jumping that first hurdle that seems scary. Its not really. The diagram above is what you are aiming to be able to see through the collimation cap you have. It wont be perfect but as good as.

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Before you start do a star test to check the state of collimation. Focus on a bright star then take it out of focus slightly, first inwardly, then outwardly. As it goes out of focus in both directions, all the circles you see should be perfect and concentric. If they are then the collimation is fine and no need to adjust.

It's common practise to do a star test after collimation as well to check that your adjustments are ok :D

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