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Collimator - not as hard as a thought it would be!


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I’ve just finished collimating my 200p dobsonian, as it was my first time doing it I was worried it would be really hard. It turns out it wasn’t, it was only the primary mirror that was out, and it only took about ten minutes turning the adjustment screws to get it collimated. It was quite simple using the instruction manual and a guide online. I can’t wait to use it now it’s properly collimated, maybe at the weekend if the sky is clear!

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Posted (edited)

“ I can’t wait to use it now it’s properly collimated, maybe at the weekend if the sky is clear!”
 

… and then you can apply the ultimate test - a star test! 🤞 Have fun!

Edited by Floater
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First time I did it it took 4hours I had to leave it over night that was on a 150p (6") 3/4 years later I stripped a 200p down flocked it did another little mod using a thin washer and a circle cut out of a milk carton. 

Put it back together collimated it in about an hour that was only because had to use two pieces of flocking. 

Now I can collimate in 5 minutes or less and that's both mirrors its like riding a bike once you have done it a few times it's easy. 

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My 1st attempt at collimation was today. Watched loads of videos to find out how it is done (what did we do before YouTube?). A friend came round to just oversee what I was doing. In the end it took me over an hour. Next I made a cuppa and by the time I came back my friend had put it all out of alignment again!

At first I was a bit miffed lol. He then explained that practice makes perfect but this time should be much easier. Even though it was really bad this time it only took about 20min. I'm fairly confident that I will find it even easier next time it needs doing. I'm quite practically minded and love to get into the technical details of things.

Looking promising for some nice clear skies this weekend where I'm looking forward to the ultimate "star test". If all is good my first target will be epsilon lyrae as I'm still to fully split the double double. Only had the scope out twice so far and I knew it needed collimating just needed to wait for the Cheshire to arrive. Always knew it was unlikely to be collimated as it was a 2nd hand buy from someone who used it twice and shoved it in the loft for 4 years. 

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I have to take out and set up my 200p every session and I find that it does go out of collimation fairly regularly so it is worth practicing. I discovered one time that one of the locking screws on the main mirror adjustment had loosened which I think caused some problems but I'm afraid to overtighten in case I distort the mirror.

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I noticed @Broadymike mentions a Cheshire.

I was just interested in how many of you use the laser type collimator.  I bought one after seeing this youtube video...   

 and also found it that easy.

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As long as the laser itself is collimated, it's ok. But if the laser doesn't sit straight, you're compensating for one error with another. You can use a barlow with a laser collimator and align the center ring of the primary on the laser collimator target. Anyway, always finish off with a star test.

http://w1.411.telia.com/~u41105032/kolli/kolli2.htm#barlowlaser

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I have a well collimated laser and a cheshire eyepiece but I tend to use the cheshire eyepiece 99.9% of the time. My 12 inch dobsonian holds its collimation well and rarely needs more than a little tweak of the primary tilt. Often not even that. Despite that I do check the collimation at the start of each session and my first observation is usually Polaris for a quick star test at high power.

Having owned the scope for quite a few years now I've become accustomed to what the collimated view through the cheshire eyepiece looks like so can see immediately if it's out and which collimation screw to adjust.

I think what can catch people out is the small amount of adjustment that is required from a collimation screw to apply enough tilt to the mirror to make the necessary difference. Often it is a very small movement of the screw - sometimes literally just a touch, that does the trick.

 

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1 hour ago, woodblock said:

It's worthwhile checking the collimation of your laser collimator. When I got mine it was miles out.

 

A cheap and quick way to do this is to roll it along a flat surface (kitchen worktop) whilst it's switched on, and look at the dot projected on the wall behind.  The dot should move in a flat line.

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I was able to align both mirrors of my 200P with a homemade cap but I now use a Cheshire sight tube . From new it was well aligned but I did need to make a small adjustment to the primary and have since tweaked the secondary. I have regularly checked both and I have found it has held its alignment.

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6 hours ago, Capt Slog said:

I noticed @Broadymike mentions a Cheshire.

I was just interested in how many of you use the laser type collimator.  I bought one after seeing this youtube video... 

I know this may sound strange but I want to start my journey into astronomy with as few technical aids as I possibly can. Yes I know a properly set up laser may be quicker/more accurate but I like the getting stuck in approach. Certainly for now a goto mount is not on my radar either. I feel like I'm cheating if I just go for the easy option. 

I had seen that video in my research already. But there were others that tempted me into the more traditional Cheshire. 

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On 11/06/2021 at 21:57, Broadymike said:

Yes I know a properly set up laser may be quicker/more accurate but I like the getting stuck in approach

I'm not sure a laser is necessarily quicker or more accurate. However, I use the laser for last minute adjustments of the primary when it is dark in the field. In daylight I would use a Cheshire.

With regards collimation of the laser the cheap ones are usually miles out. I made a little collimation rig out of a few bits of lego and it is now spot on (or at least a mm or two at 8 metres).

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