Return to the Cloudy Nights Telescope Reviews home pageAstronomics discounts for Cloudy Nights members
· Get a Cloudy Nights T-Shirt · Submit a Review / Article

Click here if you are having trouble logging into the forums

Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu… uh, User

Equipment Discussions >> Reflectors

Pages: 1 | 2 | 3 | 4 | 5 | (show all)
droid
rocketman
*****

Reged: 08/29/04

Loc: Conneaut, Ohio
Re: Andy's Shot Glass Video - Wish He Would Correct It new [Re: johnnyha]
      #5668443 - 02/08/13 08:10 AM

Still working on getting someone whos traveling south, to bring me back a bottle of rebel yell.

I find Jack daniels makes any telescope work like the hubble, rivers on the moon and all


Post Extras: Print Post   Remind Me!   Notify Moderator  
csrlice12
Postmaster
*****

Reged: 05/22/12

Loc: Denver, CO
Re: Andy's Shot Glass Video - Wish He Would Correct It new [Re: droid]
      #5668560 - 02/08/13 09:23 AM

Don't foget to take off the mouthcap first!

Post Extras: Print Post   Remind Me!   Notify Moderator  
jrbarnett
Eyepiece Hooligan
*****

Reged: 02/28/06

Loc: Petaluma, CA
Re: Andy's Shot Glass Video - Wish He Would Correct It new [Re: ed_turco]
      #5669906 - 02/08/13 10:32 PM

Andy's Newtonian was a 10" f/4.7, so fast enough that proper textbook collimation would call for offset that whould be noticeable, but...

Honestly, if you collimate even an f/4.5 exactly as he suggests, with no offset, you probably won't notice the difference visually 9 nights out of 10 in the west and 99 nights out of 100 in the east.

Regards,

Jim


Post Extras: Print Post   Remind Me!   Notify Moderator  
Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: Andy's Shot Glass Video - Wish He Would Correct It new [Re: jrbarnett]
      #5670021 - 02/09/13 12:55 AM

Quote:

Andy's Newtonian was a 10" f/4.7, so fast enough that proper textbook collimation would call for offset that would be noticeable, but...

Honestly, if you collimate even an f/4.5 exactly as he suggests, with no offset, you probably won't notice the difference visually 9 nights out of 10 in the west and 99 nights out of 100 in the east.

Regards,

Jim



Jim,
If you center the secondary in the tube and under the focuser, the process of collimation tilts the optical axis slightly towards the focuser. This is often referred to as the "New Model" of collimation. The result is actually full offset for the secondary and the angle of intersection at the secondary is slightly more than 90 degrees. You see the same off-center shadow of the secondary you would were the secondary mirror offset in the tube and the optical axis coincident with the center line of the OTA.
The point is, you cannot achieve a complete concentricity to all images and be collimated. THAT'S what is wrong with the video.


Post Extras: Print Post   Remind Me!   Notify Moderator  
johnnyha
Postmaster
*****

Reged: 11/12/06

Loc: Sherman Oaks, CA
Re: Andy's Shot Glass Video - Wish He Would Correct It new [Re: Starman1]
      #5670035 - 02/09/13 01:26 AM

Quote:

The point is, you cannot achieve a complete concentricity to all images and be collimated. THAT'S what is wrong with the video.




Perfectly spoken.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Nils Olof Carlin
Carpal Tunnel
*****

Reged: 07/26/04

Re: Andy's Shot Glass Video - Wish He Would Correct It new [Re: jrbarnett]
      #5670126 - 02/09/13 04:11 AM

Quote:

Andy's Newtonian was a 10" f/4.7, so fast enough that proper textbook collimation would call for offset that whould be noticeable, but...




Maybe "offset" could be better understood than it usually is now.

Think of the position of the fully illuminated field:
You would want it (at least reasonably) centered in the focuser. This is perhaps easiest acheved by centering the secondary using a suitable sight tube (for want of one, you could, usually with poor precision, use the focuser drawtube). If you do, the shadow of the secondary reflected in the primary, will necessarily be decentered relative to the reflection of the focuser and the cheshire, collimation cap etc. The decentering depends on the focal ratio, but how obvious it is depends, I think, more on the relative size of the focuser and the secondary - if they are fairly close, as in smaller instruments, the more obvious it is.
And that is of course the heart of the subject at hand - a few of the posters apparently have never noticed, others have. Beginners trying to learn collimation can, as we know, be utterly confused by the fact that they fail to get everything concentric as some unsuitable video or manual will say. (They probably do not try the non-obvious trick to center the reflections of the secondary and focuser - you move the secondary away from the primary. This, of course, makes the secondary (not reflected) be displaced, very obvious in a sight tube, less so without one. Also not so obvious is that the fully illuminated field is shifted in the same direction, the negative aspect particularly in beginner size instruments.)

Don't think offset - think optical centering of the secondary, and do it simply with a sight tube (easily made!).
But most of all, avoid instructions that suggest that everything seen in the peephole will be nicely centered. It simply can't be done!

Nils Olof


Post Extras: Print Post   Remind Me!   Notify Moderator  
rmollise
Postmaster
*****

Reged: 07/06/07

Re: Andy's Shot Glass Video - Wish He Would Correct It new [Re: Starman1]
      #5670286 - 02/09/13 08:27 AM

Quote:


Jim,
If you center the secondary in the tube and under the focuser, the process of collimation tilts the optical axis slightly towards the focuser. This is often referred to as the "New Model" of collimation. The result is actually full offset for the secondary and the angle of intersection at the secondary is slightly more than 90 degrees. You see the same off-center shadow of the secondary you would were the secondary mirror offset in the tube and the optical axis coincident with the center line of the OTA.
The point is, you cannot achieve a complete concentricity to all images and be collimated. THAT'S what is wrong with the video.




But the other point is, a beginner can collimate using the easy instructions on Andy's video and get excellent images. Images indistinguishable from someone whose umptysquats and thises and thats are CONCENTRIC!


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jason D
Postmaster
*****

Reged: 10/21/06

Loc: California
Re: Andy's Shot Glass Video - Wish He Would Correct It new [Re: rmollise]
      #5670402 - 02/09/13 09:51 AM

Quote:

But the other point is, a beginner can collimate using the easy instructions on Andy's video and get excellent images



I believe you are still missing the point of this thread. This thread is not about "offsets" or about getting soft views at the eyepiece. This thread is about many beginners getting confused and frustrated following Andy’s video because their actual collimation cap view shows non-concentric circles unlike the illustrations used in the video.
Jason


Post Extras: Print Post   Remind Me!   Notify Moderator  
FirstSight
Duke of Deneb
*****

Reged: 12/26/05

Loc: Raleigh, NC
Re: Andy's Shot Glass Video - Wish He Would Correct It new [Re: rmollise]
      #5670459 - 02/09/13 10:26 AM

Quote:

Quote:


Jim,
If you center the secondary in the tube and under the focuser, the process of collimation tilts the optical axis slightly towards the focuser. This is often referred to as the "New Model" of collimation. The result is actually full offset for the secondary and the angle of intersection at the secondary is slightly more than 90 degrees. You see the same off-center shadow of the secondary you would were the secondary mirror offset in the tube and the optical axis coincident with the center line of the OTA.
The point is, you cannot achieve a complete concentricity to all images and be collimated. THAT'S what is wrong with the video.




But the other point is, a beginner can collimate using the easy instructions on Andy's video and get excellent images. Images indistinguishable from someone whose umptysquats and thises and thats are CONCENTRIC!




SO: What exactly would one need to physically do during initial setup of the secondary/primary and the collimation process to be able to get the perfectly concentric end-result shown in Andy's video? Under what circumstances would following the steps indicated in his video in fact lead to perfectly concentric results (are there any unstated assumptions necessary to make it work?). Corollary question: under what circumstances would this result in a well-collimated vs miscollimated scope? (As distinguised from say, a result which produces, especially in slower focal-ratio scopes or at lower magnifications, a plausibly-enough viewable image that is nonetheless not an optimally tuned one?)

One common set of circumstances where it will assuredly NOT result in neat concentricity is if the secondary is first centered under the focuser with a sight tube. The reason why has been explained in several posts above.

Edited by FirstSight (02/09/13 11:02 AM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: Andy's Shot Glass Video - Wish He Would Correct It new [Re: rmollise]
      #5670519 - 02/09/13 11:09 AM

Quote:

Quote:


Jim,
If you center the secondary in the tube and under the focuser, the process of collimation tilts the optical axis slightly towards the focuser. This is often referred to as the "New Model" of collimation. The result is actually full offset for the secondary and the angle of intersection at the secondary is slightly more than 90 degrees. You see the same off-center shadow of the secondary you would were the secondary mirror offset in the tube and the optical axis coincident with the center line of the OTA.
The point is, you cannot achieve a complete concentricity to all images and be collimated. THAT'S what is wrong with the video.




But the other point is, a beginner can collimate using the easy instructions on Andy's video and get excellent images. Images indistinguishable from someone whose umptysquats and thises and thats are CONCENTRIC!



Actually, my earlier statement was poorly stated. It should have read:
"The point is, you cannot achieve a complete concentricity to all images. The process of collimation guarantees they won't be. THAT'S what is wrong with the video.



And judging by the number of threads that start out with confusion over that fact, the number of videos and books with inaccurate information must be large.
Look, align the mirror tilts ignoring concentricities and secondary mirror placement and you will be collimated and have fun with the scope. It's simple. Even if the field is not perfectly illuminated or the focal plane is even slightly tilted. But the video doesn't tell people to ignore that, and the images shown are misleading.


Post Extras: Print Post   Remind Me!   Notify Moderator  
astro_baby
scholastic sledgehammer


Reged: 06/17/08

Loc: United Kingdom
Re: Andy's Shot Glass Video - Wish He Would Correct It new [Re: Starman1]
      #5670727 - 02/09/13 01:11 PM

When I came back into this hobby from an age when there were no fast scopes I did use Andys video and I did in fact find it misleading as it showed a concentric pattern that was impossible to achieve with my F5. LOTS of other guides online showed the same thing and this created confusion to my brain...

After much pulling of hair out, wailing and gnashing of teeth I finally got it sorted about offset largely through a thread on here and some PM to/from Jason.

The result was me building a collimation guide which I hoped would find a mid point between high end collimation guides and the overly basic ones but which would cover off all of the issues.

The guide gets a lot of use judging from page stats on my site but I too have taken stick from people about some areas of it.

The fact is you have to strike a balance between a complete guide covering every possible aspect (with the risk a newbie just passes out from fear looking at it) OR you create a guide covering the basics and hope the reader if confused with take on further reading. I get people moaning about my guide saying its too basic and also people moaning that its too complicated. They are few and people who find the guide useful are many so I am happy with that.

I always amend my guide if I get a few people saying the same thing.

I'd always encourage people to have a go at writing one themselves and getting it reviewed for accuracy because the more info available the better.

I did find Andys guide confusing but I cant knock folk who are willing to invest time and effort to get this stuff made. I know from experience my own guide took a boatload of time to do. Its getting the pictures, making diagrams, writing text, proofing it, turning it into a nice page layout. I cant recall how long the collimation guide took but I would bet it was at least two days work and probably more.

My view is if it helps a single person not to have frustration then its worth it.

If I had clearer skies I wouldn't bother writing guides cos I aint that altruistic but when you live in a country where clear skies are rare then its at least something to do to keep your own interest up and maybe help a tyro.


Post Extras: Print Post   Remind Me!   Notify Moderator  
rmollise
Postmaster
*****

Reged: 07/06/07

Re: Andy's Shot Glass Video - Wish He Would Correct It new [Re: FirstSight]
      #5670874 - 02/09/13 02:49 PM

Quote:

SO: What exactly would one need to physically do during initial setup of the secondary/primary and the collimation process to be able to get the perfectly concentric end-result shown in Andy's video?




Who cares? Joe or Jane Novice can collimate easily with his instructions, point the scope at objects in the sky, and have a hell of a good time. The images will be good, and they will not have spent time when they should be under the stars worrying about pea-picking collimation.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jason D
Postmaster
*****

Reged: 10/21/06

Loc: California
Re: Andy's Shot Glass Video - Wish He Would Correct It new [Re: rmollise]
      #5670894 - 02/09/13 03:07 PM

Quote:

Who cares? Joe or Jane Novice can collimate easily with his instructions,



Our concern is not Joe or Jane who can follow his instructions and accept the final results but our concern is with John or Jan who follow his instructions and get frustration with the lack on concentricity collimation view.
You seem to belittle the challenges of collimation for beginners. Try to tell a frustrated beginner who comes to CN seeking collimation assistance that collimation is way too easy. This is the last thing that frustrated beginner wants to hear because it implies he/she is incapable of executing what is perceived to be an easy task.
Collimation is easy for me today but I always remind myself on how difficult, frustrating and scary it was when I attempted it for the first time including the confusing non-concentric view. I never tell anyone who seeks collimation assistance that collimation was too easy because I know it is the last thing frustrated beginners want to hear.
Jason


Post Extras: Print Post   Remind Me!   Notify Moderator  
rmollise
Postmaster
*****

Reged: 07/06/07

Re: Andy's Shot Glass Video - Wish He Would Correct It new [Re: Jason D]
      #5670900 - 02/09/13 03:14 PM

I think you are worried about nothing. The beginners will be OK. Amateur astronomy survived seveal generations of collimation tools made of 35mm film cans with icepick holes in the bottom, afterall.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Jason D
Postmaster
*****

Reged: 10/21/06

Loc: California
Re: Andy's Shot Glass Video - Wish He Would Correct It new [Re: astro_baby]
      #5670903 - 02/09/13 03:19 PM

Quote:

When I came back into this hobby from an age when there were no fast scopes I did use Andys video and I did in fact find it misleading as it showed a concentric pattern that was impossible to achieve with my F5. LOTS of other guides online showed the same thing and this created confusion to my brain...




Hello Mel,

It is always good to hear from you. I can't count the number of replies I read in astro forums that include statements such as: "Refer to Astro_Baby's guide. It shows the secondary mirror shadow shifted due to offset especially for fast scopes". All these replies are in response to beginners who get confused by the lack of concentricity and your guide has been assisting them to alleviate that confusion.

Jason


Post Extras: Print Post   Remind Me!   Notify Moderator  
astro_baby
scholastic sledgehammer


Reged: 06/17/08

Loc: United Kingdom
Re: Andy's Shot Glass Video - Wish He Would Correct It new [Re: Jason D]
      #5671076 - 02/09/13 05:29 PM

Thanks Jason and hi to you too and hope you are well.

The lack of concentricity totally messed up my head. More so because I was used to old fashioned slow scopes collimated with a glorified film cannister. My reflector circa 1977 had a colimation tube supplied with the scope. I cant recall its exact F ratio but it would have been about F8.

I just found the inability to get the circles concentric AND centred under the focuser was a real brain ache. Not being an optical expert I just clildnt understand why it was impossible. I cant be the only one as I see this come up on forums so often.

I have to be honest, unlike you Jason I just dont respond to collimation threads these days because it does my head in and its so hard to diagnose what a users peoblem may be from screenshots.
I know that sounds like I am being a bit of a cow but i found all my time was being absorbed answering collimation issues.

The other reason is I am not that expert, i can collimate my scope and most other scopes in my hands but I lack the theoretical knowledge to handle much else.

With regards go Andys tutorial it was one of the things that baffled me but it did at least get me to a kind of first base so it dis have its uses. Pesonally I think lasers in the hands of a novice cause more problems than they ever solve not least because most scopes dont have an accurate enough focuser to make a laser useful.


Post Extras: Print Post   Remind Me!   Notify Moderator  
droid
rocketman
*****

Reged: 08/29/04

Loc: Conneaut, Ohio
Re: Andy's Shot Glass Video - Wish He Would Correct It new [Re: astro_baby]
      #5671293 - 02/09/13 07:38 PM

My dear old dad alwasy said if you want something done right ,do it your self.

Sounds like a plan ,who wants to do it???

Its easy just make a video and post it on the net.....


Post Extras: Print Post   Remind Me!   Notify Moderator  
jmartin
super member


Reged: 08/25/08

Loc: Corpus Christi, TX
Re: Andy's Shot Glass Video - Wish He Would Correct It new [Re: droid]
      #5671417 - 02/09/13 08:54 PM

Worrying about the concentric rings is where collimation anxiety comes from (oh my god, it's not 1000000000% correct). Enjoy your scope and forget about it. Or make your own video simple as that. I used Andy's video and it worked great for me.

Post Extras: Print Post   Remind Me!   Notify Moderator  
FirstSight
Duke of Deneb
*****

Reged: 12/26/05

Loc: Raleigh, NC
Re: Andy's Shot Glass Video - Wish He Would Correct It new [Re: droid]
      #5671650 - 02/10/13 12:14 AM

Quote:

My dear old dad alwasy said if you want something done right ,do it your self.

Sounds like a plan ,who wants to do it???

Its easy just make a video and post it on the net.....




I said that back many posts ago in this thread, at least twice. That's Andy's privilige to decline to accept the constructive criticism that's been well-articulated on this thread, and keep his video the way he wants. And it is up to those of us offering the constructive criticism to eventually come up with an alternative (there, that's at least three times). The major hurdle in doing so isn't so much understanding how to present accurate material in a manner suitably clear and straightforward for beginners; rather the challenging part is creating material with high-quality production values, graphics, and animations. I'll grant Andy that his video has superb production values and graphics, is stylistically well-presented, and shows that he put a lot of effort into it, regardless of the issues many of us have about certain substantive particulars.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jason D
Postmaster
*****

Reged: 10/21/06

Loc: California
Re: Andy's Shot Glass Video - Wish He Would Correct It new [Re: jmartin]
      #5671752 - 02/10/13 02:39 AM

Quote:

Worrying about the concentric rings is where collimation anxiety comes from (oh my god, it's not 1000000000% correct). Enjoy your scope and forget about it. Or make your own video simple as that. I used Andy's video and it worked great for me.




Good advice but how do you suggest passing it to beginners? Beginners do not know which alignments are critical and which ones are not. Beginners do not understand why their collimation cap view is non-concentric and if they should ignore it or not. Passing the correct knowledge to them and help them avoid getting frustrated is the point of this thread.

If Andy's video is in some obscure website then this thread would not have existed. Because Andy's video is popular and google directs beginners to it, it would be a good place to pass on these collimation related messages.

Jason


Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1 | 2 | 3 | 4 | 5 | (show all)


Extra information
22 registered and 17 anonymous users are browsing this forum.

Moderator:  ausastronomer, Phillip Creed, JayinUT, okieav8r 

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled


Thread views: 4123

Jump to

CN Forums Home


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics