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Another Collimation thread, but different


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Hey guys, I have a starblast 4.5 f/4 and I'm trying to collimate it, and have been trying for the past 3 days non stop. No matter how perfect I seem to get it in the collimation cap, when I point it at a light and defocus, I get something like this: http://brucegary.net/RCX/CollimationNeeded.png
I'm very patient and dont mind it taking this long, but the fact that I've made no progress over 3 days is just getting to me. I feel like theres something I'm doing wrong even though Im following all the tutorials that have been posted on this forum. When I look through my collimator cap I see this http://www.astro-baby.com/collimation/actual%20view%20slow%20scope%20collimation.jpg

Why are the results on lights differing than the ones I see in the collimation cap?

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You need at least a Cheshire, IMHO.  I've seldom seen anyone be successful using only a collimation cap on a fast scope.

Clear, Dark Skies

I didn't want to waste that money right now but I guess I have no choice, just ordered a cheshire. 

Thanks for the heads up!

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I'm not very knowledgeable when it comes to collimation, only mine! But Astrobaby's collimation guide for my make of scope says there's an offset of the secondary for fast scopes. See here:

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

But I don't know if that's anything to do with the offset that you're seeing. Probably not!

Alexxx

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Unfortunately a fast scope tends to "look" different when you perform collimation on it. The view that you get when collimating an f/6 newtonian is different to that for an f/4 newtonian. In effect what can happen is you de-collimate the scope.

To add insult to injury a fast scope needs collimating more frequently then a "slow" scope.

Have a read of astro-baby's guide (a couple of times), then give it a go.

I will also add that ultimately you are mechanically aligning the assorted optical axis and getting mirrors both central and orthogonal. The use of a Cheshire is to validate this alignment.

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Hi once you get the Cheshire it will all fall into place people over complicate the process and I have seen page after page once the secondary is set ,(usually at the factory and it hardly needs doing) the primary his easy,

I check every time mine goes out just carrying mine out side moves the primary a little it can look hard as you read the guides on line and they shlw loads of diferent pictures it's a mine field

Pat

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With a basic collimation cap my F4.8 Newtonian always looks a bit off.

A slightly defocused bright star tells the truth.

But with the collimation cap, I've learned which direction and how much it looks off, so still gives useful info.

Regards, Ed.

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I use both a Cheshire and collimation cap. The cap gives me a wider field of view. With the Cheshire I can't see the mirror clips. But that's probably just me being bad at it! :grin:

No, I get the same in my 250px; cap to see the clips, then Cheshire to align it all.

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