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Andy's Shot Glass Video - Wish He Would Correct It

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#1 FirstSight

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Posted 04 February 2013 - 09:13 PM

Andy's Shot Glass Collimation Video is a well-known web resource with wonderfully good intentions to help instruct new owners of newtonian reflectors how to go about collimating their scopes. The graphics are very clear, the explanations are very articulate and understandable, and it's very well-produced: in short, this would be, should be the kind of resource the astro community should be very grateful to have available to steer people to to learn the basics of collimation with elementary tools.

UNFORTUNATELY, it contains some items of egregiously incorrect information which undermine an otherwise solidly sound presentation. I know it takes a fair amount of effort to produce a good-quality, clearly understandable technical instruction video, but nevertheless the particular flaws in this presentation have been known for quite some time now, and I'm perplexed that Andy has so far apparently made no attempt to issue an updated, corrected version of his video.

Here's the main flaws:
1) He states that when the collimation process is successfully complete, all the reflections are lined up neatly concentric. This is not true of the innermost reflection of the secondary in the primary, which (in order to hit the optical rather than geometric center of the secondary mirror) is offset toward the focuser such that its outline will appear to rest tangent to the next circle out rather than concentrically centered within. This effect is *not* merely an artifact of using a fancy toolkit such as the Catseye Blackcat (cheshire) instead of a simple collimation cap; the effect is the same viewd through my Orion combo tool, which for purposes at hand is effectively nothing more than an improved version of a collimation cap. See, e.g. this picture from the Catseye website of how this proper offset looks, although in this case we are also seeing artifacts of using the BlackCat Cheshire, which does not however negate the essential point.
2) He states that the Orion Lasermate is "accurate", when the sub-premium 1.25" lasers in this class (and Orion's in particular) are notorious for themselves being significantly out-of-collimation right out of the box. So long as this miscollimation-of-laser isn't too severe, secondary mirror alighment is more forgiving than primary alighment in that so long as the secondary alignment still reflects the entire primary and isn't otherwise very severely off, the consequences from mild misalignment are merely slightly uneven illumination or loss of a few percentages of illumination efficiency...barely noticeable, if at all. And so, overlooking flaws in the laser beam's own alignment can be forgiven in the context of the secondary. NOT SO WITH RESPECT TO THE PRIMARY. The Orion Lasermate deluxe is equipped with a white screen projecting the return beam of the laser off the primary, with a hole in the middle of the screen which the user seeks to align the beam with. However, despite the superficial resemblance of this to e.g. the screen of a TuBlug in a barlowed laser setup, the Orion Lasermate is NOT a barlowed laser setup, but rather projects the direct image of the return beam itself, which even with an accurately collimated laser is NOT sufficiently accurate to insure reliable collimation of the primary mirror, especially in scopes whose f-ratios are closer to f/5 or below than f/6 (and Andy's XT10 scope shown in the video is f/4.7!!)
3) At the outset of the video, Andy states that the larger the scope, the more often it needs collimation, which is only accidentally, inconsistently sometimes so because the true relationship is that mis-collimation tolerance diminishes as the scope's focal-ratio grows shorter (and larger scopes often tend to be made with shorter focal-ratios than smaller scopes, but this isn't necessarily true, e.g the f/4.0 Orion Starblast 4.5".)

If I had a camera setup suitable for shooting a more accurate collimation video, this is something I'd love to undertake. Actually, not to put other folks up to tasks instead of doing work myself, but Jason and Don Pensack have each advanced vastly further in constructing accurate, well-illustrated tutorials than I have, and so have Vic Menard and Nils Olaf Cardin, but these all tend to be presented on a more sophisticated level better absorbed after a bit of experience with the equipment. No one has yet produced a good substitute for Andy's popular, but in too many important respects, misleading basic video for beginners. I wish Andy himself would undertake to correct his otherwise good video: he would richly deserve the praise and gratitude of the astro community if only he would do so.

Chris Mohr
 

#2 ed_turco

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Posted 04 February 2013 - 09:18 PM

If you weren't making short focus telescopes (f/4.5), this offset business wouldn't even trouble you. Perhaps Andy was speaking of f/6 or f/8 mirrors.

Why not write to him listing your concerns?
 

#3 FirstSight

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Posted 04 February 2013 - 09:24 PM

If you weren't making short focus telescopes (f/4.5), this offset business wouldn't even trouble you. Perhaps Andy was speaking of f/6 or f/8 mirrors.

Why not write to him listing your concerns?


I'm using CN as a sounding board to critique (and if necessary, correct) my analysis *before* trying to contact Andy. However, I'm far from the first person who's noticed these particular flaws in his presentation, and similarly it's unlikely I'd be the first person informing him of these concerns.

As you say, the purported inaccuracies probably have forgivably mild impact on f/8 scopes, but lots of relative beginners who access his video have sub-f/6 scopes e.g. lots of Zhummell scopes are f/5 for example. Also, these alleged errors are not at all necessary for clarity and simplification, but are each easily correctible without introducing needless complexity in the presentation.
 

#4 David Pavlich

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Posted 04 February 2013 - 10:16 PM

Andy's a pretty good guy. He would have probably been happy to discuss his tutorial with you. Is there a reason that you had to voice your opinion here first other than being a sounding board? I'm sure Andy would want to be made aware of his need for correction, so since I know Andy personally, I'll make him aware of your concerns.

David
 

#5 FirstSight

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Posted 04 February 2013 - 10:30 PM

Andy's a pretty good guy. He would have probably been happy to discuss his tutorial with you. Is there a reason that you had to voice your opinion here first other than being a sounding board? I'm sure Andy would want to be made aware of his need for correction, so since I know Andy personally, I'll make him aware of your concerns.

David


Don't get me wrong, I think he deserves kudos for taking the effort to put together such a quality, well-articulated presentation but/for the small (but potentially important) handful of flaws I mentioned. Critiquing isn't the same as condemning. But why not run my own critique before a knowlegeable critical audience first, before contacting Andy? Seems like a good idea to me...especially since I don't dismiss the possibility that in some respects, I myself could be wrong or could stand correction or clarification.
 

#6 Jason D

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Posted 04 February 2013 - 10:48 PM

In Chris's defense, many of us over the years pointed out that major error in the video's illustration that shows everything concentric.

Here is a 5 year old post -- one of many made by me and others
http://www.cloudynig...ber/2144693/...

I do not know if Andy is still active in astronomy or if he would have the interest to edit his old video.

Jason
 

#7 GeneT

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Posted 04 February 2013 - 11:03 PM

Maybe Andy can re-shoot and correct his original video.
 

#8 johnnyha

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Posted 05 February 2013 - 12:01 AM

Yes it's more a case of, how could he NOT know by now? The most egregious mistake is the concentric circles, this has been responsible for countless threads from people upset that their secondary shadow is not concentric even though they have done everything apparently right - and they have! The shadow should be offset towards the focuser. Because of this video it has to be repeated over and over and over.
 

#9 David Pavlich

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Posted 05 February 2013 - 08:58 AM

He got the message and video will remain. It's meant for a neophyte that wants to see stuff, not read a PhDs disertation and not spend a lot of money on barlowed lasers that cost more than their $250 Newt.

David
 

#10 FirstSight

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Posted 05 February 2013 - 09:40 AM

He got the message and video will remain. It's meant for a neophyte that wants to see stuff, not read a PhDs disertation and not spend a lot of money on barlowed lasers that cost more than their $250 Newt.

David


The mistakes I critiqued aren't even remotely graduate-level material, but instead rather elementary, and potentially quite substantive errors that many folks will later need to un-learn to gain consistent collimation proficiency. They're not even justified as simplifications for the sake of introductory clarity for relative beginners, when accurate information would be just as clear and straightforward to present as inaccurate information.

BTW: the notion that a "barlowed" laser setup is a $250 investment is another needlessly (and wildly) inaccurate statement on his part, if that's what he said. First, anyone can easily convert an ordinary inexpensive barlow, e.g. the $30 Astro-Tech 2x barlow to a barlowed laser setup using little more than a piece of pierced white cardboard. Second, even the most elegant high-end prefab commercial barlowed setup, the Glatter TuBlug, is only $75 in 1.25" format.

Andy may indeed be generally a "pretty good guy" and I give him abundant positive credit points for taking the effort in the first place to create a well-produced collimation video for the benefit of the astro community. I could understand and respect his reluctance to do a corrected update to his video if his reply was along the lines: "yeah, it would be good to do that, but it took so many hours to create the existing version that it's difficult to find the time to re-do it." However, instead his response (at least as you report it) now comes across more as bullheaded stubborness and unwillingness to accept constructive criticism.

I should state what provoked my recent attention to this in the first place. Our local astronomy club periodically stages "telescope tune-up" clinics for neophyte non-members, which are regularly led by one of our members who has put together a really nice introductary general presentation of nuts and bolts of telescopes and observing which he presents at these events. However, he's primarily an SCT guy, and he's been using Andy's Shot Glass video at these presentations for the reflector folks in the audience. I've pointed out the flaws in this video to him, but unfortunately it's also true that there's not really an alternative good basic instruction video available (yet, anyway). At these clinics, I sometimes find myself explaining to newbies why the innermost reflection isn't concentric after I've finished helping them collimate their reflector, contrary to Andy's video. And so, I didn't just tee this subject up randomly in order to be a smarty-mouth curmudgeon, but because it's sowed actual confusion I've had to try to clear up.

Also David, why didn't you wait and let me attempt to contact him after I had vetted my critique here to insure its accuracy before approaching him? I get the impression that the cup is now a bit poisoned for me to attempt a diplomatic approach to him, regardless of whatever manner you may have communicated it to him first.
 

#11 rmollise

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Posted 05 February 2013 - 10:00 AM

1. Some folks offset their secondaries. Some don't. Not critical IMHO, and certainly not necessary for longer scopes. Also, it is just confusing for novices who much of Andy's excellent material is aimed at.

2. Orion's widget can produce a good collimation. I know because I have used it for field collimation clinics at star parties. I still prefer my good old combo Cheshire/sight tube, but plenty of folks would consider it SUB PREMIUM, too. A beginner most assuredly doesn't need to go all OCD on collimation and spend for barlowed 400 buck gadgets. That is the kind of stuff that just bogs 'em down for no good reason. ;)

3. I don't find the StarBlast needs collimation frequently at all if it is done right in the first place and locked down. In general larger scopes _do_ require more frequent collimation. That's the penalty for larger, heavier primaries in lighter truss tube bodies.

My verdict on Andy's Shotglass? Extremely well done and valuable for novices. ;)
 

#12 FirstSight

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Posted 05 February 2013 - 10:22 AM

2. Orion's widget can produce a good collimation. I know because I have used it for field collimation clinics at star parties.


I still have my Orion widget, even though I don't use it any more for my own scopes because I also now have the Catseye and Glatter tools. I keep it especially for use at telescope tune-up clinics or any other setting where the person I'm helping owns similar tools. I even still have my Orion 1.25" laser, which is useful when helping folks with similar tools or whose focuser is only 1.25" since my Glatter is 2" only - but it's nevertheless a good idea to teach others what the flaws of the Orion laser are, and when and how to they need to work around these flaws to make it a still-useful tool.

If the matters I mentioned were just graduate-level theoretical stuff which was nevertheless always inconsequential in practice, there would be no reason to stir the pot over Andy's presentation as-is. If accurate clarity was difficult to achieve in a basic presentation without indulging some potentially problematic simplifications, likewise there would be inadequate reason to stir the pot.

However, I'll just have to respectfully disagree with you on this Uncle Rod. I mean no disrespect to the service Andy has tried to bring to the astro community with the tremendous effort that obviously went into creating his presentation. However, that fact does not immunize his work from valid constructive criticism.
 

#13 Jason D

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Posted 05 February 2013 - 10:23 AM

He got the message and video will remain. It's meant for a neophyte that wants to see stuff, not read a PhDs disertation and not spend a lot of money on barlowed lasers that cost more than their $250 Newt.

David


David, I believe Andy got the message years ago and the fact the video remained shows that he decided long time ago not to change it.
Your response is little harsh. Those who get confused by his video and by most scope manuals that show perfectly concentric circles do not seek PhD level knowledge. I for one was very confused with the shift of the secondary mirror silhouette when I started on this hobby.
Having said the above, I do not believe Andy is obligated to change his video. If he does not want to change it, that is OK. Those who get confused will eventually be shown the way in forums or by knowledgeable friends.
Jason
 

#14 rmollise

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Posted 05 February 2013 - 10:29 AM

You're free to criticize him, I'm free to criticize him. That's not the point. The point is that his pages are clearly aimed at beginners, and that the things you find disturbing will really be of no consequence for them.

Me? I ain't that sophisticated, I guess, but I would much rather a novice collimate with a dadgum collimation cap and start looking at and enjoying the sky than begin obsessing over offsets and other things that will, frankly, have an extremely minor effect on images in any telescope. ;)

I have no doubt that your criticisms come from the heart, and that you think these things are important and want to spread the word. And for some venues they indeed might be. For Andy's starry-eyed beginner, though, I'd have to say "not so much." For them, simple, or even "quick and dirty" is better. Something I've learned from my own missteps with novice amateurs and my university astronomy students over too many years. :cool:
 

#15 FirstSight

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Posted 05 February 2013 - 10:34 AM

He got the message and video will remain. It's meant for a neophyte that wants to see stuff, not read a PhDs disertation and not spend a lot of money on barlowed lasers that cost more than their $250 Newt.

David


David, I believe Andy got the message years ago and the fact the video remained shows that he decided long time ago not to change it.
Your response is little harsh. Those who get confused by his video and by most scope manuals that show perfectly concentric circles do not seek PhD level knowledge. I for one was very confused with the shift of the secondary mirror silhouette when I started on this hobby.
Having said the above, I do not believe Andy is obligated to change his video. If he does not want to change it, that is OK. Those who get confused will eventually be shown the way in forums or by knowledgeable friends.
Jason


Since Andy is apparently unwilling to update his video, the alternative is to either live with it and hope most people eventually grow out of any early misimpressions they get from this otherwise good aid, or else...take the trouble to create an alternative video for the web. As fable of the hen making bread goes, unless and until I'm willing and able to help make bread on this (and not expect e.g. Jason or Vic etc. to do it for me)...I'll just have to live with helping newbies one-on-one with gaining accurate understanding whenever they're confused by any oversimplifications or inaccuracies about collimation. Perhaps this would be a worthwhile project to undertake, but it's just words of good, but empty intentions unless and until I actually got going on it.
 

#16 David Pavlich

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Posted 05 February 2013 - 11:17 AM

Lose your present knowledge and you're in your living room with your new XT8 with your collimation cap and you want to get out and see stuff. You look at the directions and read:

" This is not true of the innermost reflection of the secondary in the primary, which (in order to hit the optical rather than geometric center of the secondary mirror) is offset toward the focuser such that its outline will appear to rest tangent to the next circle out rather than concentrically centered within."

I know exactly what you mean, but what do you think the beginner sitting in his living room is now thinking? Was I a bit harsh? Perhaps, however, unless this beginner is an optical engineer or a Physics major, the above just sent the beginner into a tailspin.

The natural progression is to get the scope out, clean up the collimation as best he can with his cap, see things and then ask questions. Andy's video will improve the cap results. Then he can dig deeper and find ways to refine what he's seeing.

It was my wording about the balowed laser. Again, put yourself in the beginner's living room. He has no clue about barlowed anything, let alone building one.

I'll leave it at the fact that Andy's video is a help to simplify things for a beginner which is how it was intended. When the beginner gets a bit more knowledgeable, he can dive into the nuances of collimation.

David
 

#17 csa/montana

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Posted 05 February 2013 - 11:27 AM

My verdict on Andy's Shotglass? Extremely well done and valuable for novices.



Agreed; this video was a great help to me in understanding the mystery of collimating, when I first started with my 8" dob. I was hopelessly confused. This video gave me the basis of collimating to go on & enjoy astronomy. Was it precise & 100% correct? I didn't know or care, as after applying his instructions, I actually could see something with my scope! :grin:

As I gained knowledge (from these forums), I refined my collimating further, with better tools; I don't feel the video stunted my understanding of how to properly collimate at all, rather got me on my way to a very enjoyable life of viewing.
 

#18 Nils Olof Carlin

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Posted 05 February 2013 - 11:38 AM

I can only agree with Chris' very constructive criticism of the video.
As Chris writes, and Johnny reinforces, and Jason and others have pointed out since long ago:
showing and claiming that all "lines up so nicely" will indeed confuse (and has indeed confused) many a the beginner, trying in vain and in desperation to make things concentric. Does anyone think a correct statement here would really make things more confusing than that?

All that is needed is a short comment that the reflection of the collimating cap and the dark shadow of the secondary may not appear quite concentric even if everything else is, and need not be - it's all right that they are not. This is not PhD stuff, but it is basic telescope optics, and David, there is no need at all to bring up offset in the context.

Less critical:
The illustrations show a frame of black around the optics, with a distinct circular opening in which you center the secondary. This, I think, poorly represents reality, where the focuser drawtube may be much too short and wide to reliably make the secondary "centered in the whole view" (cf. the diagram in the beginning of the video).
Inexact centering will make the focuser axis off, more or less - then again, maybe the beginner really does not need to worry about the focuser axis (cf. Gary Seronik's collimation article in S&T last sept.).

In the process of adjusting the primary, Andy says: "I see the reflection of my eye down there". The beginner might take this to mean that the collimating cap is removed at this stage, which it should not be. You can't then literally see your eye - without the centered peephole, you can not center your eye in the focuser to a meaningful accuracy.

Also, even if the laser collimation is done, it would be prudent to check the primary's adjustment with the collimation cap - easily done to get the best precision that simple collimation can get.

David wrote: "He got the message and video will remain." ??
All the more reason for somebody skilled with video to make something better suited to the needs of the beginner. I am not aware that any of the many collimation videos on Youtube qualifies (I am sure I have not seen them all).

"Everything should be made as simple as possible, but not simpler."

Nils Olof
 

#19 ed_turco

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Posted 05 February 2013 - 11:50 AM

Gee, after all this discussion and dissertating :), all I've used on my f/6s and longer is a thread spool, which came in 1.25" diameter and has a 6mm hole in it. And it was free. :jump:

Never had a worry about collimation.

Ed :bow:
 

#20 Jason D

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Posted 05 February 2013 - 12:05 PM

" This is not true of the innermost reflection of the secondary in the primary, which (in order to hit the optical rather than geometric center of the secondary mirror) is offset toward the focuser such that its outline will appear to rest tangent to the next circle out rather than concentrically centered within."


How about:

"Refer to the attached illustration. It represents what you will see through the collimation cap for a well collimated scope. Note: Ignore the spider vanes reflection position and the secondary shadow indicated by the arrows. These might look out of alignment"

Attached Files


 

#21 Jason D

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Posted 05 February 2013 - 12:18 PM

Even better, why can't the video and scope manuals include a real picture of what is expected to be seen via the collimation cap for a well-collimated scope. Something similar to the attachment.

Posted Image
 

#22 David Pavlich

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Posted 05 February 2013 - 01:11 PM

Jason, I have no beef with you or anyone else's capability. After I learned the basics, I dug around and found the sites that show how to fine tune a Newt. All Andy did was make a video that simplifies what some consider a black art when they enter the world of Newtonians.

I would suggest that someone produce an Advanced Collimation Video and post it. There's enough people here with the expertise to do it. Include all the proper tools and how they work as well. It's like processing a CCD image. Tony Hallas can take my data and make it look like a Hubble image. But guess what....Tony didn't do that when he had his first images sitting in Photoshop. It took him a lot of time and effort to get to the top in his field.

At any rate, I'll leave it there. I don't want to give my fellow moderators a headache. :grin:

David
 

#23 Jason D

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Posted 05 February 2013 - 01:46 PM

I believe you are reading too much into our posts. I believe the general theme of replies is that Andy's video is good and it could be better with a minor update.
Jason
 

#24 FirstSight

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Posted 05 February 2013 - 01:55 PM

I believe you are reading too much into our posts. I believe the general theme of replies is that Andy's video is good and it could be better with a minor update.
Jason


Exactly. The proposed corrections under discussion do not require introducing anything at all difficult to correctly explain or present, nor to understand by a neophyte. They do, however require someone, whether by way of Andy himself or someone creating an alternative basic collimation tutorial video, to apply the necessary time and effort, which may not be quite so trivial an undertaking.
 

#25 Nils Olof Carlin

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Posted 05 February 2013 - 02:02 PM

I would suggest that someone produce an Advanced Collimation Video and post it.

So far, this thread has been about wanting a basic collimation video, much like like Andy's, with the confusing and potentially misleading parts (look back the thread to see them specified) corrected - not more complex, just more right. If Andy is satisfied leaving his own video as is (see the title of this thread), our hope goes to someone else. We are a couple here who know collimation at any desired level (some can make not only beautiful but also correct illustrations!) - but who is good at video making?

Nils Olof
 






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