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1.25" Laser Collimator

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#1 asaint

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Posted 19 May 2005 - 10:58 AM

1.25" Laser Collimator

#2 Vic Menard

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Posted 19 May 2005 - 12:29 PM

Where to start...

Let's start at the end. You can get a quality 1.25-inch laser collimator from Howie Glatter for $100--and for $85 more you can add quality holographic and Barlowed laser attachments. Now that's about twice (and a half) as much as the laser reviewed, but it's much more useful and the resulting collimation is meaningful!

As the reviewer indicated, the instructions for these lasers are often oversimplified. Quoting from the article:

"In theory, if your telescope's collimation is pretty close to "on," the returning laser dot should appear somewhere on this grid, then you simply use the primary adjustments to move the beam until it disappears back into the same hole it came out of.  That's the gist of it as explained in all the catalogs, but there's more to it than that."

I'll say! Following these instructions is more likely to result in a miscollimated primary mirror, especially when you consider the loose tolerances quoted in the article. If the beam doesn't accurately intercept the center of the primary mirror to begin with, the return beam seen inside the window of the target area will have an error equal to the vector sums of the errors at both contact points! This is the main reason the Barlowed laser is enjoying so many positive reviews--it's relatively insensitive to focuser axis (diagonal "aiming") errors. For this reason, I recommend using a simple point source laser only for setting the focuser axis (diagonal "aiming"), and only using the return beam as a rough estimate to be corrected later with a Cheshire or Barlowed laser.

On the subject of collimating one of these inexpensive lasers... I tried collimating a non-window variety at a star party last week. I could get it close, but I couldn't get it close enough to use. I didn't have my dial calipers with me, but I suspect the barrel was egg-shaped.

My sincere advice is to save your money and get a better tool that doesn't need to be taped to fit properly--one that will deliver consistent results. If you're a serious amateur, you'll appreciate the difference immediately. If you're a beginner, you will have a tool you can trust, and the good images to prove it.

#3 Andy S.

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Posted 19 May 2005 - 08:30 PM

I don't have much to say to this other than that my Orion Laser Collimator Deluxe works great and fits snugly into my crayford focuser. Yes, I have to tighten the set screw a bit but there is no wabbling arround. Maybe the review should be for the particular make and model reviewed and less intendet as a broad overall reviev for the less expensive lasers??

#4 Guest_**DONOTDELETE**_*

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Posted 22 May 2005 - 10:06 PM

Just a couple of thoughts:

On an equatorial mounted reflector, place the focuser so it is vertical. That way the heavy laser can't sag and mess up things.

A quick check of the laser aligment is to simply rotate it in the focuser. The spot on the primary should not scribe an arc.

With the laser in place, rack your focuser in and out a bit. If the spot swings around on the mirror, you're probably doomed....

Daniel

#5 Vic Menard

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Posted 23 May 2005 - 08:00 AM

On an equatorial mounted reflector, place the focuser so it is vertical. That way the heavy laser can't sag and mess up things.


Assuming of course, that the laser is heavier than the most massive eyepiece you plan to use :). This is probably more of a focuser/adapter (if used) issue.

A quick check of the laser aligment is to simply rotate it in the focuser. The spot on the primary should not scribe an arc.


I agree that an arc would be unacceptable. A small circle caused by an unsecured laser could be caused by precession. Tightening the lock screw on the focuser drawtube (and adapter) eliminates precession and should deliver a consistent "read". A helical focuser, unless it's very well made, will probably cause the laser beam to precess uncontrollably...

With the laser in place, rack your focuser in and out a bit. If the spot swings around on the mirror, you're probably doomed....


If the laser is properly secured in the focuser, this indicates that the focuser has potentially serious mechanical issues.

Each of these points demonstrates the sensitivity of a simple point source laser to focuser axial errors--alignment, drawtube function, and mechanical registration and tolerances (and we haven't even considered the diagonal mechanicals!) As long as the cause of the axial defect can be positively identified (and either corrected or allowed for given the specific "acceptable" tolerances), the laser is just doing its job!

#6 Andy S.

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Posted 23 May 2005 - 10:15 AM

I think it is a fact that it is one thing to Collimate the primary and diagonal with a croshairs EP and laser and another to put in your observing ep's.
If you have a crummy focuser, you may collimate as much as you want, there will always be a little wiggling in the bad focuser, especially the rack and pinion ones that come with soo many of the "cheaper" scopes. But that obviously has nothing to do with the laser. I believe that if you know what you are doing, you kann use the laser for quick in the field collimation and the cheshire EP for a more refined collimation at home during the day. I only use the laser and it works just fine for me. Startests are generally successfull. So I must be doing something right.

#7 Vic Menard

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Posted 23 May 2005 - 10:38 AM

Andy,
I think we're in agreement (assuming the laser is properly collimated of course!) At f/4.9 your primary mirror axial collimation tolerance (for "good" performance) is about 0.022-inch. That's pretty easy with a Cheshire eyepiece or Barlowed laser--but with a simple point source laser, because the primary mirror collimation (on the target inside the window) is the vector sum of both axial errors (focuser axis AND primary mirror axis), you will need to read both alignments to an accuracy of about 0.01-inch. It's doable, but, generally speaking, the Cheshire eyepiece or Barlowed laser is easier and more precise (which makes a BIG difference as the focal ratio gets even shorter!)

Still, you say you're getting good results, and that's what counts! My concern is for those individuals who have less expertise than you and cannot understand why laser collimation results can vary so dramatically.

#8 Matthew E

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Posted 23 May 2005 - 11:39 AM

i have a Synta Stock focuser and am running in circles with collimation, if i rack in and out just a 1/4 of a turn the laser will have changed position, i have ordered a moonlite CR1 and am waiting for it, until then i think i will not bother collimating.

#9 mnaf

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Posted 21 April 2007 - 01:55 AM

After doing a lot of research on laser collimators I finally bought one, second hand, similar to the model in this review. A "certified" unit, it came with it's own very nice oak v-block with a rubberized bottom and a magnetic sheet between the v's to hold the adjustment allen wrenches.

I really wanted a Glatter but several things swayed me to this model:
It's collimatable.
Has the rear view port.
Came with it's own v-block.
Was supposedly already aligned.
Was $30-120 cheaper than a Glatter.

When I received it, it was not aligned as stated. The laser dot (which isn't as much a dot as a short dash) rotated visibly. However, after about 15 min. I was able to align the laser to within 1/16 in. (0.06") over 21 ft. - virtually unnoticable rotation. Only having it for a week, I don't know how well it will hold this accuracy but having done it I know I can repeat it.
With time and determination, I think a user-collimatable unit like this could be very, very accurate. (This unit was supposed to be pre-aligned to 0.1" over 6.6')

Oh yeah, and it needed 2 layers of cellophane tape for a snug fit. :p

As I write, I'm waiting for clear skies to try it and to use it barlowed - the real reason I wanted a laser. I already have a combo cheshire-sight tube and a reasonable understanding of collimation. The idea of barlow-collimating from the back of my f/4.9 reflector is pretty interesting. Can't do that with (or collimate) a Glatter.

BTW, I totally agree that the marketing for "typical" laser collimators over simplify the process and ignore the issues and pitfalls of accuracy and laser-collimation!

Mike

#10 Jon Isaacs

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Posted 21 April 2007 - 04:55 AM

>>>Where to start...

Let's start at the end. You can get a quality 1.25-inch laser collimator from Howie Glatter for $100--and for $85 more you can add quality holographic and Barlowed laser attachments. Now that's about twice (and a half) as much as the laser reviewed, but it's much more useful and the resulting collimation is meaningful!

....

My sincere advice is to save your money and get a better tool that doesn't need to be taped to fit properly--one that will deliver consistent results. If you're a serious amateur, you'll appreciate the difference immediately. If you're a beginner, you will have a tool you can trust, and the good images to prove it.

-----
Hi:

I think Vic makes a nice case for the quality laser, I can just add my personal experience. I have used a few lasers but mostly my 8 year old Howie Glatter. My main scope for most of those years has been a 12.5 inch F/4.06 Discovery, a serious challenge to collimate.

The Howie Glatter arrived collimated, it has never needed collimation and it is a nice "slip fit" in the focuser. I have replaced the battery once during that time. It cost $100. It is not fancy, it is a quality tool, simple, well made and robust. In the long run, I believe a quality tool is the cheapest way to go because you only spend make one purchase instead of two.

Jon

#11 Vic Menard

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Posted 23 April 2007 - 09:53 AM

...The idea of barlow-collimating from the back of my f/4.9 reflector is pretty interesting. Can't do that with (or collimate) a Glatter.

http://www.collimator.com/
All Glatter lasers "feature" accessible collimation screws (although I've never had to touch them.) There is also a Glatter "window" attachment pictured on the website, which would make Barlowed laser alignment from the rear of the scope possible. I know Howie prefers the Barlow target to be mounted inside the OTA for a balanced alignment, and as long as you can see past the primary mirror, there's no need for a window attachment.

The Glatter Blug is a good solution for many users. When I use one, I prefer to position the Blug so it's facing toward the front opening of the OTA to improve the accuracy of the critical primary mirror axial read. At f/4, my primary mirror axial alignment needs to be almost perfect (less than 0.025-inch.) It's much easier for me to see the alignment up close than from the rear of my scope (although I can get a good coarse alignment from the rear.)

#12 sixela

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Posted 25 April 2007 - 01:37 AM

Personally, I tend t use the BLUG from the back and then a BlackCat from the front for the final touches.

#13 lunar mike

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Posted 26 April 2007 - 02:15 PM

I have never had any tools cheshire/sight tube, laser , artificial star, I always start test ed and I thought I was pretty good at aligning my sct and reflector.
I just got an 8 inch tube for my svp mount things are a little shaky anoter matter. I use the cheshire to align my focuser to the secondary first with cheshire . Then I line the main mirror up and then I use the orion deluxe laser sight on the primary at the end to see how all else is . I find my laser to beeing really good. then the star test and occasional artificial star test. so I use a couple methods and I know know how far off I actually was but I knew where to start first

#14 Starman1

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Posted 01 May 2007 - 12:34 PM

This article eloquently makes my point that an inexpensive laser, if used as directed, will result in poor collimation of the scope. That wasn't, I know, the intention of the article, but it was it's inadvertent, between-the-lines, conclusion.

There was another thread here on CN where someone was arguing in favor of the out-and-back single beam laser collimation until someone showed how a scope could be grossly out of collimation and still give a perfect out-and-back beam alignment.

It means a sight tube, at least, is necessary for proper secondary alignment.

And an autocollimator is necessary to eliminate the residual errors in read on the other tools, whether laser or passive.

And if you already have the sight tube and autocollimator, why not buy a good cheshire and simply avoid the laser in the first place?

I think a laser is a powerful tool in the hands of someone who has already learned the ins and outs of collimation, but that doesn't describe the beginner just seeking to collimate the scope for viewing. And the inaccurately-collimated lasers (with small rectangles for "spots") that are often provided or purchased just make miscollimation a surety.

I know that many people understand and use lasers for collimation, and if you already have that level of skill in collimation, a laser can be a useful tool. I use one for a "check-up" in the middle of the night.

But I can't recommend lasers for collimation to anyone who doesn't already have a set of passive tools. And neither should any of the other experienced collimation experts on this site. If a scope owner can't afford both types, the passive tools should win out for the proper selection of collimation tools because they can do more than a laser and they are more likely to be collimated "out of the box". That there is one exception (Glatter) doesn't invalidate my assertion.


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