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Demonperformer

WORRY-WART! ... or "What was all the fuss about?"

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To put this in perspective, I bought my first SCT nearly ten years ago. And in all that time, there has been one word that has scared me witless (no, that's not a spelling mistake :)) ... collimation!!!!

There are so many horror strories around of people scratching corrector plates and simply messing it up completely and making a scope unusable, that I have always avoided it like the plague ... once even preferring to sell the scope I had and buy another one to avoid having to do it [don't you just love the logic of that one?particularly when there is no guarantee they will arrive collimated!]. I've always belonged to the "I don't care about winning, I just don't want to lose" brigade.

Six months ago, I bought an RC6 and recently picked-up a cheshire eyepiece. No corrector plate ("But don't drop the allen key into the tube," the websites warn!). If I'm ever going to do this, now is the time. A quick look earlier this week showed the dot well out of position, so yesterday ... I procrastinated ... o come on, you didn't think it was going to be that easy, did you? But there are clear skies predicted for tonight, so this morning I went outside, set up my NEQ6, plonked the RC6 onto it, pointed it slightly downwards and went and made a cup of coffee. Returning to the scope I started to have a play.

I kid you not. In less time than it had taken me to set up (excluding the coffee), I had the black dot slap-bang in the middle of my white circle. The allen bolts were tight, yes, but not "wheel-nut" tight; not "you need three feet of metal bar wrapped around the allen key to lean on in order to loosen it" tight. And yes, my first move was in the wrong direction ... so what??? It was so monumentally, stupidly easy ... why all the horror stories on the internet?

Am I pleased I set it up outside where there was plenty of space, rather than struggling in the lounge? Yes. Am I pleased I got a cheshire so I could do it in daylight? Yes. Were the ten years of worry that I had endured dreading this day a waste of energy? You bet!

So my message is to anyone who looks at the word "collimation" and immediately becomes a rabbit in headlights ... Action Cures Fear ... seriously, just do it ... if I can do it, ANYONE can.

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Yes, I've collimated scopes - not that difficult and well worth it.

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Can I bring the horror back into this story? :D

You are collimating RC scope, and while it's not difficult, it's not easy as that either :D

RC has hyperbolic surfaces, and although you have your mirrors centers aligned, it does not mean that scope is fully collimated. You need to adjust tilt of both mirrors properly as well. This can't be done with simple tool like collimation eyepiece.

If you don't have laser collimator, best way to do it is by measuring curvature across sensor. It sounds complicated, but it's not. You need to focus on a star in center of the field and then move that star to each of the corners. Any defocus that you get from field curvature needs to be the same in all for corners.

You can easily know if you need to do it - just take an image with the scope and check the corners. If all four corners have round stars, you are good, but if any corner displays astigmatism more then others (or combination of corners) - you will need to fix the tilt of primary.

Here is a good guide how to do it:

https://deepspaceplace.com/gso8rccollimate.php

And don't worry, it is as easy as the first step you have done, just lasts a bit longer as it's iterative - adjust secondary, adjust primary, then secondary again, then primary ... :D just a few rounds should be enough to get you good collimation.

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TBH, I have yet to try with my Mak 150. (I sense it is a "bit out"!?) ?

But my "cheap & cheerful" TS F/4 Newt arrived with the 2nd'ary
almost hanging off. lol. I had to: "Be Bold...  Be Bold" (Mr. Horne) ?
(This is doubtless only understandable by our older UK readers!)

It's a balance between putting people off and learning DIY stuff. ?
I have sometimes missed out by delaying "having a go" at stuff...

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As per Vlaiv, it's not as easy as an SCT, it's a different beast all together and there are a few folk on here that ended up getting rid of RCs after spending / wasting hours trying to take decent images with them.

Just saying :grin:

Dave

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I've collimated Newtonians and sct's and it's been ok so far. The only bit that is a pain is star testing where you can't physically look through then eyepiece and adjust the primary at the same time, resulting in some back and forth, especially if you forget which way is which with the adjustments.

You can take collimation to a higher level, for example I know my newtonian focuser isn't quite square but it's plenty good enough and I wouldn't dare mess with focuser alignment as I fear I would get into a pickle.

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I've just purchased a Howie Glatter laser with the concentric ring attachment to do the same thing on my RC8....... I may attempt to do it tonight.

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2 hours ago, martin_h said:

I've just purchased a Howie Glatter laser with the concentric ring attachment to do the same thing on my RC8....... I may attempt to do it tonight.

It's supposed to be real easy with said collimation laser - you should be able to do it even indoors against any flat surface like regular wall.

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My question is, when you sold the scope to avoid collimating it, did you up grade in size.

I could possibly fool SWMBO by saying, "you know, I'm saving money!!"

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Best of Luck D, just make sure you collomate with the extentions in place that get your camera in focus or collomate to the intended point of focus as that's where collomation matters most and with the added extentions and standard crayford focuser if disassebled and reassebled pryor to  your next imaging session collomation will likely be off as it was the case with my RC. Of course I was using mine for visual but I imagin the same constraints would apply...

                          Freddie...

 

                           

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9 hours ago, maw lod qan said:

My question is, when you sold the scope to avoid collimating it, did you up grade in size.

Getting a larger one was the excuse I use, but I am now in the process of downsizing again, hence the RC6.

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9 hours ago, SIDO said:

Best of Luck D, just make sure you collomate with the extentions in place that get your camera in focus or collomate to the intended point of focus as that's where collomation matters most and with the added extentions and standard crayford focuser if disassebled and reassebled pryor to  your next imaging session collomation will likely be off as it was the case with my RC. Of course I was using mine for visual but I imagin the same constraints would apply...

                          Freddie...

I'm not picking on you particularly, but I think this demonstrates one of the problems facing the collimation-newbie. So much of the information that is available is conflicting. The advice I read on t'internet about RC collimation is (1) don't add the extension tubes, and (2) you will only need to do it every couple of months.

Then some people say that you can only do it properly with a star (so why buy a cheshire eyepiece??). They tell you to tilt the telescope downwards (so you don't drop anything into the tube) but, from my location at least, there are precious few stars that are visible when the tube is pointed downwards ... particularly stars that are at the zenith - that's when they're not telling you to use one at “about 45° altitude”. In addition to which, even ignoring the dewshield, I can't see of collimation screws when the scope is on the mount and pointing to the zenith.

Is it any wonder that people get scared-off of even attempting it?

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1 hour ago, Demonperformer said:

I'm not picking on you particularly, but I think this demonstrates one of the problems facing the collimation-newbie. So much of the information that is available is conflicting. The advice I read on t'internet about RC collimation is (1) don't add the extension tubes, and (2) you will only need to do it every couple of months.

Then some people say that you can only do it properly with a star (so why buy a cheshire eyepiece??). They tell you to tilt the telescope downwards (so you don't drop anything into the tube) but, from my location at least, there are precious few stars that are visible when the tube is pointed downwards ... particularly stars that are at the zenith - that's when they're not telling you to use one at “about 45° altitude”. In addition to which, even ignoring the dewshield, I can't see of collimation screws when the scope is on the mount and pointing to the zenith.

Is it any wonder that people get scared-off of even attempting it?

Oh I get it, did you notice my advice came from past experience with the RC6 ?

The unit I toyed with had focuser run out issues so I wound up selling it at a loss...My own fault I guess for wasting my 90 day warrenty thinking I could remedy the problem, don't know if that's a typical issue though I thought to mention it...

Its ok to pick on me a little, All part of the collomation fun ?

 

 

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Posted (edited)

Hmm... maybe I won't buy an RC6!  Oh!  I wasn't intending to...  ?  I'm skint!

Edited by Gina
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I think I've all the telescope I need, want and can afford now.

I went years with bad collimation after fitting the C8 SCT with a set of Bob's Knobs. Tried to collimate a few years back and made it worse. Last summer tried again and got it pretty damn close.

Strange thing was that last summer it was easy whereas before no adjustments improved it, no matter how hard I tried.

 

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