3 Quick Collimation Questions

[Jasonb]

Yep, I found it helpful to check the primary first. Like I said, it seemed to work for me, and hopefully a star test will confirm that.

[AlexK]

In the long run I would highly recommend to invest ~$20 into the cheap laser collimator. If you have any Barlow lens at hands, the "Simplified Barlowed Laser Collimator" method is the easiest for quick and accurate primary's alignment checking and adjustment on most any reflector. E.g.: https://www.amazon.com/Generation-Telescope-Collimator-Newtonian-Telescopes/dp/B00OXKHZTC

I heard about decent seeing conditions rarity on the Islands, so that could be a good alternative to the star test (which requires ether great seeing or years of experience performing it with a particular instrument).
 

Edited March 5, 2021 by AlexK

[Spile]

18 hours ago, AlexK said:

In the long run I would highly recommend to invest ~$20 into the cheap laser collimator.

Interesting in that the sites I use recommend just the opposite.

Still if it works for you!. I will stick to the "KISS" approach of just a collimation cap. 

[AlexK]

5 hours ago, Spile said:

Interesting in that the sites I use recommend just the opposite.

Still if it works for you!. I will stick to the "KISS" approach of just a collimation cap. 

Collimation cap method is not accurate enough for 1:5 reflector already. You must follow with the Star Test. While the Barlowed laser has a 2x zoom getting you much closer to perfection, and totally foolproof.

[Spile]

17 hours ago, AlexK said:

Collimation cap method is not accurate enough for 1:5 reflector already. You must follow with the Star Test. While the Barlowed laser has a 2x zoom getting you much closer to perfection, and totally foolproof.

That is not my experience. If collimation using a cap results in a star test showing my telescope is collimated that is fool proof to me and demonstrates that there is no benefit in introducing another tool.

I am happy to follow the following advice...

Gary Seronik’s no-tools collimation advice https://garyseronik.com/a-beginners-guide-to-collimation
The Small Optics guide at https://www.youtube.com/channel/UCVi6UI5BvXm9lyZg5AG0X1g/videos
Collimation myths at http://web.telia.com/~u41105032/myths/myths.htm
Zen and the art of collimation http://uncle-rods.blogspot.com/2009/07/zen-and-art-of-telescope-collimation.html?m=1

 

[AlexK]

18 hours ago, Spile said:

That is not my experience. If collimation using a cap results in a star test showing my telescope is collimated that is fool proof to me and demonstrates that there is no benefit in introducing another tool.

I am happy to follow the following advice...

Gary Seronik’s no-tools collimation advice https://garyseronik.com/a-beginners-guide-to-collimation
The Small Optics guide at https://www.youtube.com/channel/UCVi6UI5BvXm9lyZg5AG0X1g/videos
Collimation myths at http://web.telia.com/~u41105032/myths/myths.htm
Zen and the art of collimation http://uncle-rods.blogspot.com/2009/07/zen-and-art-of-telescope-collimation.html?m=1

You see? Four guides already, with a decent amount of quite dense information to comprehend, remember, and follow. With plenty of steps and turns where something may go wrong. The Star Test is an art on its own, which is well known to be used wrong as well. All because we are all different as biological beings. That's why the Scientific Method has been developed eons ago, so we all could 100% agree on something at last and don't be stuck in the analysis paralysis forever (how good is good enough?).

In this case, we want a simple way to measure the problem in a easy to comprehend way and monitor the progress of our effort to fix a misalignment. The direct situation assessment with your eye doesn't always work well here. The direct analogy of the problem is the doctor with the stethoscope listening to your heartbeat and deciding if your condition needs certain treatment or another (that's your approach). Yes, it is a very simple, actually trivial procedure for a doctor, no single doubt. Even though with certain limitations (e.g. the patient is moving vigorously or can't breath). But not at all for an average Joe even in the most refined environment of an optical bench. Joe would instead benefit much more placing his hands on the handlebar of the fitness machine and seeing his heartbeat and ECG on the screen to pace the exercise in the real time. The ring around the hole on the Barlowed laser collimator (BLC) screen is exactly the same approach. No professional medical personnel needed.

If you were lucky to afford using a full OTA Newtonian telescope (as opposed to a truss, including collapsibles, which cannot hold the general collimation after packing down, and which is the primary subject of the above 4 guides of well established ATMers), then after the initial collimation, the secondary will never need any adjustments. Only the Primary may have some play from the real-life handling (e.g. you had to have it standing on its collimation screws as you forgot to setup your mount first). And for that the simplified BLC method I'm recommending from my personal experience above is the best method to use in the field (as opposed to the comfort of your deliberately equipped and well lit man's cave) just prior to the observing session, even in the total darkness, if/when the Star Test doesn't work well yet, e.g. due to the primary's thermals still settling, or bad seeing, or no 2xDmm magnification eyepiece at hand, or due to the lack of experience. So you can be sure that your telescope can't show Jovian storms' fine structure not because of its ill collimation. Just eyeballing the eyecup hole concentricity is not enough as the eye has parallax and resolution limitations. That's why there are so many collimation tools on the market all the way to over $1000 in price.

Besides, all 4 sources you have mentioned are quite dated. Super cheap laser collimators arrived on the market around 2018.

Edited March 8, 2021 by AlexK

[Spile]

20 hours ago, AlexK said:

You see? Four guides already, with a decent amount of quite dense information to comprehend, remember, and follow. With plenty of steps and turns where something may go wrong. The Star Test is an art on its own, which is well known to be used wrong as well. All because we are all different as biological beings. That's why the Scientific Method has been developed eons ago, so we all could 100% agree on something at last and don't be stuck in the analysis paralysis forever (how good is good enough?).

In this case, we want a simple way to measure the problem in a easy to comprehend way and monitor the progress of our effort to fix a misalignment. The direct situation assessment with your eye doesn't always work well here. The direct analogy of the problem is the doctor with the stethoscope listening to your heartbeat and deciding if your condition needs certain treatment or another (that's your approach). Yes, it is a very simple, actually trivial procedure for a doctor, no single doubt. Even though with certain limitations (e.g. the patient is moving vigorously or can't breath). But not at all for an average Joe even in the most refined environment of an optical bench. Joe would instead benefit much more placing his hands on the handlebar of the fitness machine and seeing his heartbeat and ECG on the screen to pace the exercise in the real time. The ring around the hole on the Barlowed laser collimator (BLC) screen is exactly the same approach. No professional medical personnel needed.

If you were lucky to afford using a full OTA Newtonian telescope (as opposed to a truss, including collapsibles, which cannot hold the general collimation after packing down, and which is the primary subject of the above 4 guides of well established ATMers), then after the initial collimation, the secondary will never need any adjustments. Only the Primary may have some play from the real-life handling (e.g. you had to have it standing on its collimation screws as you forgot to setup your mount first). And for that the simplified BLC method I'm recommending from my personal experience above is the best method to use in the field (as opposed to the comfort of your deliberately equipped and well lit man's cave) just prior to the observing session, even in the total darkness, if/when the Star Test doesn't work well yet, e.g. due to the primary's thermals still settling, or bad seeing, or no 2xDmm magnification eyepiece at hand, or due to the lack of experience. So you can be sure that your telescope can't show Jovian storms' fine structure not because of its ill collimation. Just eyeballing the eyecup hole concentricity is not enough as the eye has parallax and resolution limitations. That's why there are so many collimation tools on the market all the way to over $1000 in price.

Besides, all 4 sources you have mentioned are quite dated. Super cheap laser collimators arrived on the market around 2018.

I am terribly sorry but your words have failed to convince me. The star test shows me that the method I am using is working. The simple approach works for me and nothing you have said above gives me a a reason to change. I certainly have no wish to introduce another tool/variable into the equation.

I think it is best to let others to do their own research and make their own judgement on what is the right method for them including the validity and suitability of the links I posted. 

 

 

Edited March 8, 2021 by Spile

[AlexK]

4 hours ago, Spile said:

I am terribly sorry but your words have failed to convince me. The star test shows me that the method I am using is working. The simple approach works for me and nothing you have said above gives me a a reason to change. I certainly have no wish to introduce another tool/variable into the equation.

I think it is best to let others to do their own research and make their own judgement on what is the right method for them including the validity and suitability of the links I posted. 

I'm not arguing with you. If you believe your collimation routine works for you fine, just keep it. You probably spent years already polishing your visual collimation skills. Besides, you've got the Flextube Dob, which is indeed require more collimation effort compared to the solid OTA of the OP. While I'm giving my advice to beginners with the solid OTA like mine, who still have a chance to stick with the much more accurate, simple, convenient, and now very cheap modern collimation aid and the proven flow eliminating any guesswork in the routine collimation check of the primary, which plagued newtonians for centuries.

I understand, the "do their own research" is a nice hobby time spending for some indeed. But the "judgement" is what smart folks are coming for here when asking on this forum. It comes with the practical experience they don't have yet (and may not get ever without trying all collimation methods in existence and following all these lengthy writeups). Don't take me wrong, all of the above writeups are valid, but they are for the initial collimation. Especially for newly built telescopes. While I'm talking about the routine collimation of the Primary only. Which doesn't have to be as tedious as the full one (but must be extra accurate, as it's preceding observations). Especially on a solid OTA Newtonian with the final step of collimation done with the cell stiffening screws making it nearly permanent.

So, officially: my personal judgement I'm offering here, coming straight from the long term personal experience with at least 4 inexpensive Primary's collimation methods, is that after just a hundred of times doing it the classic way, which is probably how Isaac Newton himself has been doing it nearly 400 years ago, it becomes just a boring chore postponing the starry sky enjoyment. But after my lengthy and bumpy trips hunting for the clear dark sky it's a must to check anyway. Thus after trying a couple of other methods and tools I'm settled on the SBLC method as it's the most effortless, efficient, fast, and easy to read and follow among most precise weather-independent methods I could find. It works naturally as soon as you have a Barlow lens in your EP kit already and the ring-like center marker on the Primary mirror of your telescope (both can be DIY fabricated). I can't even imagine anything more bulletproof than observing the dark ring concentricity on the well lit white projection screen of the typical laser collimator. Moreover, SBLC method is fixing all deficiencies of cheap ($20) laser collimators forcing us buying $300-400 offerings of the same in the past.

On a side note. The method is so quick, that in the past, before I've done the "velcro mod" on the Primary and been using very narrow AFOV EPs, I've been collimating with it prior to every planet observing session without a hesitation, as at the different (usually rather low) altitude the collimation may change a tiny bit as the mirror rocks on its supports. 

Edited March 8, 2021 by AlexK

[Spile]

There are a number of assumptions you have made above which are incorrect but I think it is better to close down this dialogue rather than continue further.

The best of luck with your endeavours. 

Edited March 9, 2021 by Spile

[AlexK]

Oh, your Skyliner is not collapsible? My bad (looked it up in Google, and it showed the collapsible 200P model for some reason, now I see it's indeed a full OTA).

Sure, no need to feel bound to the dialog, if you have said all you had on the subject already. Again, I'm not arguing with you, just using your point as the agenda
But I'd like to elaborate on a couple of items I've briefly touched above, just for beginners of course:

The "Velcro mod" I have mentioned is very beneficial for the collimation as it is gently attaching the primary mirror to its cell, so it's not freely moving in it anymore when you are handling the telescope, but not yet pinched in the rigid supports enough to cause any optical surface distortion on the nanoscale (visible in the EP as an astigmatism). That means the mirror is always settling back into the originally collimated position in the cell even after inverting the OTA upside down for a prolonged time (e.g. for the dust free storage). For many years amateurs were using thick silicone glue dabs on the cell supports for that. But Velcro dots are much easier to apply/remove/replace even in the field. Their only disadvantage is that if you leave your telescope in the open sun unprotected, the glue may soften even on HD (heavy duty) dots. But the severe heat like that is not good for your telescope in general, so better to be proactive on that problem.

The narrow AFOV EPs issue I have mentioned as well refers to the fact that your perfect collimation spot (where your virtual Star Test must show ideally concentric rings) must be within ~3/4 of the AFOV (so you have enough well collimated field for observing the object transit at high magnifications with no guiding. Obviously, an UWA AFOV EP would allow much more slack in the collimation error. Thus I don't mind the Star Test looking not ideal exactly in the center of the AFOV as soon as within the huge AFOV I can find the decent view of it just moving the disk around. In 99% of cases no Primary collimation needed again, as even a newbie can achieve that using the SBLC collimation method instantly. Even in the case the secondary is a bit off in the sighting tube (see below).

In practice, the perfect Primary's collimation of a visual instrument is essential only for planetary views and also super-close double stars views asking for really high magnification (thus the centrality of the perfect airy disk becomes essential with typical inexpensive EPs, you need to hit the narrow FOV). But for diffuse objects or most anything at low mags it's not that crucial to go all the way to the airy disk structural analysis (which is a rather rare occasion due to the atmospheric turbulence anyway).

Edited March 9, 2021 by AlexK