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Importance Of Good Collimation


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I have learned this evening that spending time and getting spot on collimation can be very rewarding especially when your losing heart with poor views. Lately I've been getting very murky views of Jupiter even with medium power and DSO's have been hopeless, I was putting it down to poor seeing conditions and my impatience to let my eyes get dark adapted.

In another topic I mentioned wanting a higher power eyepiece and worrying how the views would be affected on Jupiter, I mentioned poor views on prior obs session and collimation was mentioned, (I think it was even myself who brought it up) probably taking my own advice, I collimated the scope the other day and took it out just now, my impatience didn't let me bother with a star test, I just pointed the scope with x214 mag straight at Jupiter..........

Damn!!! What a difference!!!! I had never before seen the GRS until Now!

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I wonder if this is an issue for me.

When I completely unfocus Jupiter so its a big blur of light- I can see an eliptical image of the mirror- but its only half of the mirror. Is this normal or do I need to collimate?

What do you get when you try this with a star, say Polaris ?

Try going inwards from the point of focus and then go through sharp focus and outwards so the stellar disk expands again. You should see a small "doughnut" shape with the a dark circular shadow in the centre either side of sharp focus. If you get that then the collimation is at least more or less OK.

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I tried with a star and I got similar.

Heres a rough drawing to what I see..

Untitled.jpg

Does it look like

post-5330-0-87497500-1429574310_thumb.jp
if yes then your primary mirror optical axis is way off which could be caused by a misaligned secondary mirror. Basically, the OTA edge is in the light path as shown below:
post-5330-0-13725400-1429574343.jpg
Jason
Edited by Jason D
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I don't know if you've seen this collimation-guide. It is, hands down, one of the best. Easy to understand and not full of technical gibberish you don't need:

http://www.astro-baby.com/collimation/astro%20babys%20collimation%20guide.htm

The author of this is a member of these forums. Say 'thanks' if you bump into him!

Clear & Perfectly-Spherical Skies,

Dave

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Does it look like

attachicon.gifstar_collimation_4.jpg

if yes then your primary mirror optical axis is way off which could be caused by a misaligned secondary mirror. Basically, the OTA edge is in the light path as shown below:

attachicon.gifstar_collimation_5.jpg

Jason

Its half of one of the photos so you can only see half the mirror.

Whats the cheapest and easiest collimation tool? A cap? Or could I just use a star?

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Its half of one of the photos so you can only see half the mirror.

Whats the cheapest and easiest collimation tool? A cap? Or could I just use a star?

If you want to achieve good collimation, you need a good collimation tool. I recommend the chesire/sight-tube combo tool -- something like;

http://www.firstlightoptics.com/other-collimation-tools/cheshire-collimating-eyepiece.html

Forget star collimation. It did not work for you. Star collimation can't be used to align the secondary mirror anyway.

Jason

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Agreed regards the Cheshire/Sighting-Tube. They work very well. More accurate than using only a cap. A laser (a well collimated one) also works, but i'd suggest not using a laser as a stand-alone collimator. I use a laser and a Cheshire/Sighting-Tube. It's always nice when the two agree with each other. But I'd get the Cheshire first and becoming adept in using it before adding the laser into the equation.

Don't be scared-off by the prospect of collimating your scope. It's really not as hard as some instructions would have you believe. I think I know why people seem to be fond of publishing instructions that would make Einstein roll-over in his grave. But that would involve a course in analytical-psychology.

Clear Skies & Putting Up The Sandbags...

Dave

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It was the Astro-Baby collimation guide that I used when doing my scope, very easy and clear to understand, getting the primary mirror clips into view was difficult when aligning the secondary as I haven't made a cap yet, but the Cheshire tool really helps.

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It was the Astro-Baby collimation guide that I used when doing my scope, very easy and clear to understand, getting the primary mirror clips into view was difficult when aligning the secondary as I haven't made a cap yet, but the Cheshire tool really helps.

So is a cap not needed?

It's this bit i'd not be sure on.

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I wouldn't say a cap is "not" needed as it helps in identifying the primary mirror clips when aligning the secondary mirror, I centered my eye as well as I could on the eyepiece holder but using a cap would be more precise. If you can view the clips in a Cheshire then all the better.

Word of advice also, don't mix up the primary lock nuts with the adjustment screws like I did because it gets you nowhere!

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Agreed regards the Cheshire/Sighting-Tube. They work very well. More accurate than using only a cap. A laser (a well collimated one) also works, but i'd suggest not using a laser as a stand-alone collimator. I use a laser and a Cheshire/Sighting-Tube. It's always nice when the two agree with each other. But I'd get the Cheshire first and becoming adept in using it before adding the laser into the equation.

Don't be scared-off by the prospect of collimating your scope. It's really not as hard as some instructions would have you believe. I think I know why people seem to be fond of publishing instructions that would make Einstein roll-over in his grave. But that would involve a course in analytical-psychology.

Clear Skies & Putting Up The Sandbags...

Dave

Thanks. I'm not gonna be scared off. The thought that I'm not using my scope to its maximum annoys me!

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Not really. You will need eyeballs, a Philips Head (slotted) screwdriver, and some fingers or equivalent. And the tools of your choice: A Cheshire Sighting-Tube, a Collimation Cap, and, maybe a Laser Collimater. And patience.

It's not rocket-science. Just take your time, and feel free to ask here if you get stuck. Once again - here is Astro-Baby's Collimation Guide:

http://www.astro-baby.com/collimation/astro%20babys%20collimation%20guide.htm

Clear Skies,

Dave

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Perhaps this is a stupid question but are there any autocolumantion tools out there? 

The answer is "no"

In theory, such a tool can be made. It will involve servomotors to adjust both mirrors, a special camera in the focuser, and a computer. However, such a system will be extremely expensive compared to a simple cheshire/sight-tube combo tool. No manufacturer will be crazy enough to invest in building and marketing such a product.

Actually, someone built and marketed a simple servomotor system that controls only the 3 primary mirror knobs many years ago. The system came with a remote controller. The idea was to use the system to adjust the primary mirror remotely for large scopes. Needless to say it was not a marketable product. I am not sure if the inventor sold any units before he called it off.

There is a collimation tool called an "autocollimator". It is an interesting tool but it is not collimate scopes "automatically" as the name might suggest.

post-5330-0-97591300-1429679653.jpg

Jason 

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Well.. I put a cap on and my secondary mirror was indeed way off. I've aligned it now so that I can see the clips. Next job is to sort out the primary.

I'm assuming that if the ring in the middle of the mirror isn't dead centre then it needs doing

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