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Passive Tool Collimation and the Newtonian

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#1 mloffland



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Posted 25 August 2009 - 08:47 AM

Passive Tool Collimation and the Newtonian

#2 paul hart

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Posted 25 August 2009 - 09:09 AM

Beautiful article, thanks for writing and posting. I pretty much follow the procedure. The secondary mirror adjust with the sight tube is usually done infrequently unless something comes loose for whatever reason. I use a pretty darned close to a perfectly aligned Helix laser to get primary collimation, and the autocollimator for final adjust. I find the laser gets me close enough for faint fuzzies, but if I want to do any lunar or planetary observing, using an autocollimator is a must for final adjustments. I do use the Catseye tools and am very happy with them.

#3 helpwanted


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Posted 25 August 2009 - 08:00 PM

brilliant article, thank you Don!

#4 coutleef



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Posted 26 August 2009 - 08:01 AM

Thanks Don,

once i purchase my dob, your article will help tremendously.

#5 YankeeJeff


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Posted 27 August 2009 - 09:37 PM

The clearest explanation yet, nicely done!

#6 Sarkikos



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Posted 28 August 2009 - 09:36 AM

Great article. It merits careful reading and rereading. I find that the best course is to collimate first with a combination cheshire/sight tube and then use an autocollimator. I don't trust laser collimators. For one thing, you should collimate the laser using a v-block before you use it to collimate your telescope. Also, since a laser is so high-tech and modern, it tends to give people false confidence in them. One positive point is that you can use them to collimate in the dark.


#7 Starman1



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Posted 28 August 2009 - 12:10 PM

Thanks all for the kind comments.

It looks like there will be a version 4 before too long.
I've had requests to include instructions on how to do Classical Offsetting Collimation, and many ways to clarify statements in several sections, especially those dealing with the latest styles of autocollimator.

I've also had requests to add a section on laser collimators and how to use them. Of course, any section dealing with laser collimators has to deal with collimating the laser (some, but not most, laser collimators arrive collimated).

However, how long can the article be before it's too long to read? It may be necessary to do a thumbnail section on a "How To" for those who don't want to read 20 pages if it gets too bloated. I've resisted inserting math because I wanted a helpful field guide, but I've been requested to insert some calculations.

My original intention was to do a "How To", but somehow it's morphed into something entirely different. I don't want to write another book on collimation. Vic Menard has the definitive text (New Perspectives on Newtonian Collimation)for that.

So I have to think about what I want to add and what I don't.

#8 FirstSight


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Posted 28 August 2009 - 02:50 PM

Great article Don.

One of the problems in writing about reflector collimation is that it is much easier to succinctly understand from the experience of successful doing than it is to succinctly explain or understand from even the best explainations. Even the best, most articulate explainations sound arcanely convoluted in places to the inexperienced reader.

Perhaps that's why the "Andy's Shot Glass" video has been so widely cited and popular for giving such a clearly understandable how-to presentation that it can be readily followed even by unfamiliar novices. YES I KNOW the "Andy's" presentation contains some quite significant inaccuracies, most particularly about whether the secondary mirror's reflection should be concentric with the other images when properly aligned.

So maybe instead of (or in addition to) a future revised/extended article, it would be a particularly valuable contribution to the astro community if you or Jason could create a more accurate "how-to" collimation video to be the rival successor to "Andy's Shot Glass". Start, as you do in the article, with a *completely* misaligned, miscollimated reflector, and show not just a side-by-side pair of slides showing starting state and ideal finish, but also some of the intermediate manipulative process in getting from A to B. For example: "I've turned the bottom-left of the three collimation screws a quarter-inch clockwise turn "tighter", let's see what happened (image of where Catseye triangle is now)...looks like we need to try turning the bottom-right collimation screw about an eighth-inch counterclockwise turn "looser"...(image of where Catseye triangle is now)...well, that brought us closer, but overshot it a bit as you can see from the difference in gaps between the Catseye triangle point facing that collimation screw and the triangle points facing the two respective others. Note how turning each respective collimation screw moves the triangle along somewhat of an arc, rather than in a straight line. That's why you'll usually need to juggle manipulating two collimation screws rather than one to accomplish anything greater than a modest nudge in a given direction..."

...and so on.

I know that Vic and Nils have produced something like this for limited parts of the process (e.g. the carefully decollimated primary procedure)...but a really good complete video presentation of the whole shebang start to finish would be an invaluable contribution to the astro community.

Nearly everyone who's both *showed* someone else the process of collimating our Newt with both of us standing there next to the scope to watch what's happening....and also tried to *explain* to someone else how to go about it without any scopes handy to demonstrate (even with some pictures handy) knows how much more difficult it is to truly get the necessary concepts across with just verbal explaination and static pictures, however good they seem to us.

#9 Starman1



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Posted 28 August 2009 - 07:40 PM

Yeah, you're right.
We spend thousands of words describing what is a 3-5 minute procedure.
I've tried taking photos through the tools with only limited success. The holes aren't small enough to avoid a bit of parallax in my images.
I think a few more goodimages and photos may be called for in this text for a next version.

As for a video, I participated in the making of these videos to help a rank beginner select and use a telescope:
beginner videos
and I realize that I am not an actor and that it is as difficult to explain something in a video as it is in text.

Making a video is not my forte. I would have to employ the services of someone else who has interest in making the video. And I'm currently working 12 hours a day 6 days a week, so I have almost no time to do it. It took me months to update my last version of this article (which was also on CN) doing a few minutes a week.

Jason Khadder may be your guy. I don't think there's anything he can't do with animated presentation. I'll see if I can get him interested in supplying some animations for the next incarnation of the article.
Thanks for the suggestion.

#10 DavidC


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Posted 05 September 2009 - 10:27 PM

It's funny how you can explain to someone until your blue in the face, but you show them a few times, and they understand what you are trying to explain. I have always had great luck with the cheshire/sight tube. I use my laser for a rough alignment of the secondary, and final alignment with the cheshire/sight tube. My laser won't get the primary into great alignment, compared with the sight tube, no matter how much I try. I've double checked the alignment of the laser several times, with no luck.

#11 Mike Phillips

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Posted 12 December 2010 - 11:19 PM

This is a wonderful article, but I'm a bit confused about the statements of the newer "TELECAT XL™" and it's feature:

"Addition of the BLACKCAT XLTM reflective ring enabling the TELECAT XLTM and XLSTM to function both as a sight tube and as a Cheshire as well."

As a new user, does this mean that I would not need a telecat and CATSEYE and BLACKCAT XL Cheshires??

What's the differences?



#12 Starman1



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Posted 13 December 2010 - 12:41 AM

The Teletube XL is purely a sight tube = crosshairs on one end and a peephole on the other.
The Black Cat XL is purely a cheshire = bright ring of reflective surface on one end and a peephole on the other.
The TeleCat XL combines the two into one tool = the sight tube with a reflective ring of material inside it. If you have this, you essentially have two tools in one.
The only disadvantage of combining both into one tool is the possible confusion of having the bright ring with its dark center and the crosshairs all visible in the field of view at the same time.
If you collimate in the daytime, with plenty of light, the TeleCat works just fine.
The Infinity XL is the autocollimator, and it is independent of the other tools.

#13 Mike Phillips

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Posted 13 December 2010 - 09:08 AM

Wonderful clairification! I was thinking this was the case, but they still sell kits with both the TeleCat XL and Black Cat XL.



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