Star testing and collimating 180 Mak

[morls]

I think it's time to get 'under the hood' of my new scope, and star testing/collimation seems a good starting point. I'm reading up on some background provided by Nick and Alex (thanks!), and thought I might use this thread to ask any questions that come up (and there will be many, I'm sure).

My first step is to set up a basic imaging rig so I can post pictures of what is happening. I've pulled apart a webcam and will attach this adapter:
https://www.bintel.com.au/product/bintel-webcam-adapter/

Once I get things set up I'll post some images of star tests. This will also give me a good reference point before I start with collimation.

Here are some of the sites I've found so far:

http://www.bbastrodesigns.com/ratemirrors.html

This one is good, (I hope it's OK to link to another forum here - in this case the page is archived) https://www.cloudynights.com/topic/315558-guide-to-star-testing-maks/

https://www.bbastrodesigns.com/JoyOfMirrorMaking/StarTesting.html

And as suggested by Nick: https://www.telescope-optics.net/index.htm#TABLE_OF_CONTENTS


Cheers
Stephen

[nsavage]

I’m interested to know what webcam you’re using.

[morls]

Hi Nick,

I'm using a HD 720p webcam I got from Jaycar a couple of years ago, not sure of the model. It has a threaded socket over the sensor so I'm hoping the Bintel adapter will work.

This video has been my guide:
https://www.youtube.com/watch?v=1gF6iHrZ4Rw

[Wavytone]

Pretty sure at the prime focus of the scope the webcam will only show points - it won’t resolve the airy disk cleanly as the pixels are too big.

Eyepiece projection or 3X Barlow may be needed.

[morls]

I've had a couple of nights with the webcam - it's a lot of fun on the moon. It's also been good for developing my focus technique. I haven't had any success with recording star testing, I think that I'd need a better setup as Nick suggested.

After playing around with the cam it's always a pleasure to go back to visual - the moon has been stunning with my 35mm Panoptic. I've done some more star testing, and I think the scope needs some minor collimation. I'm expecting a new diagonal soon - just using the stock one at the moment. Is it a good idea to wait until the new diagonal is fitted before collimating?
Cheers
Stephen

[doppler]

Hi Stephen

Here's a link to a daylight collimation check method. As for using diagonals during collimation, I would think leaving it out would reduce chances of introducing errors.

http://www.robincasady.com/Astro/collimation/

Rick

[morls]

Thanks Rick, that's a really useful link. The out of collimation image corresponds with what I'm seeing with the star test. It's not way out, but in need of some adjustment.
I'm a bit nervous about collimating this scope, mainly because I haven't done it before. I've collimated my old reflector many times, but never a closed tube.

[TareqPhoto]

I really wish to see any image of planets done with this 180mm Mak and using 3x Barlow producing very high quality image, not just a good image or so so, i really wish.

[doppler]

This is probably the best I have managed with a gso 2.5x barlow and my skywatcher 180mm mack cass and zwo120mc.

[TareqPhoto]

That is nice, but still not a high quality or mind blowing as from C14 or C11, and i asked with 3x Barlow, but you did a great job, thank you very much!

[doppler]

A fairer comparison would be with a c8, remember the 180 mack is only 7" aperture and a slow f15

[TareqPhoto]

Exactly, so that i was thinking what is a big jump from 7" [180mm] should be? C11 won't be really a big jump, C14 yes, but anything else? any another big jump from 180mm and not C14 only?

[doppler]

The big jump from a 180mm Mak is the f ratio, f15 down to f10 is a leap astro imaging wise. The C11 has the same focal length but is much faster. Resolution also increases with aperture. Of course the biggest factor for high magnification imaging is the need for good seeing, here in the tropics it's usually pretty ordinary.

[TareqPhoto]

f10 is nice, but in planetary sometimes people even go higher to f20 or f25 even f30, so i assume that focal ratio isn't a critical factor here, they all mention aperture or focal length over f ratio.

[morls]

I'm still in 2 minds about what to do regards collimation. Is it something to avoid unless absolutely necessary due to complexity? I've read differing opinions on this.

The skywatcher manual doen't mention collimation. There are 3 sets of 2 screws on the back. Are there locking screws which need to be loosened before adjusting, or are all screws part of the adjustment system?

Thanks
Stephen

[TareqPhoto]

I never touched the screws of 180mm and the collimation is good, i was going to damage it or modify or whatever just only because some are talking about collimation, i just ended up ignoring all that and using the scope as it is, turned out it is really nice and no issues, maybe i am lucky with this copy of mine.

[morls]

That's interesting Tareq. Mine is pretty darn good too. I haven't touched anything since buying it brand new. My normal way of thinking is to check things to make sure shipping and handling hasn't unsettled anything. From what I gather these scopes hold collimation very well, so any adjustments would likely be fine tuning, and then the scope should be stable for a good while.

[mental4astro]

To collimate or not collimate? - THAT is the question

So, you have a new scope, Mak, SCT, Newt, dob, whatever. The image it throws up "is pretty good" you reckon so you don't make any adjustments. That's fine.

But remember this - astro is ALL about pushing the very limits of optics to get the very best image your gear can give you. Astro is pretty much the most punishing application of optics that there is! So while you may be happy with the current image your scope gives you, if it is out of collimation, you are only cheating yourself out of the very best your precious scope can give you. So, you have a darn nice scope, but without getting the optical alignment right, the scope effectively has a "black eye"...

At the factory, there are time pressures to push out scopes, or you may have got a scope collimated at 4:00pm on a Friday arvo with the technician paying more attention to the clock than the job at hand, or the technician may feel near enough is good enough, or the technician doesn't know how to get the collimation any better. So the stuff coming straight out of the factory may or may not be good, but rarely is it as good as the scope can be.

So now, after doing all your research, spending your hard earned cash, and feeling pretty good with your purchase, the way I see it you owe it to yourself to become really well acquainted with your scope so YOU can squeeze every single photon into where it should go.

"Scared" about stuffing something up? What are you scared of? If things do go pearshaped, THAT is actually a good thing! You learn from your mistakes, AND this site and others like it are here to help you get it right!, or did you forget that! :) Believe it or not, I still "stuff up" the collimation process, and sometimes stuffing it up is part of the "getting it right" process! Sometimes the element that you do adjust is not the one that actually needed tweaking, and it is only by stuffing up that you become aware of this.

Oh, and another thing, as your experience grows, so does your visual acuity, and you will pick up on things not being quite right. So while at first you may not notice that the collimation isn't quite right, YOU WILL, and it will bother you like a stone in your shoe! :lol: And then what? Are you going to leave that stone in your shoe? :question:

Alex.

[Outcast]

Sheesh your posts drive me nuts sometimes Alex.... :)

But, in a good way....

Having already done some 'tweaking' of the mechanics of my recently acquired LX90 8" and, being pushed by others to become way more anally retentive about the precision of my setup & star alignment process now, I'm gonna have to give some serious thought to the whole collimation process....

I really wanted to avoid this but, now I feel compelled....

Thanks...

[mental4astro]

:cool: :cool: :party: :party: :jump2: :jump2:

Mission accomplished! :lol:

It's not hard tweaking a scope. But it does require patience and time to understand. I guess it is a bit pedantic, but you didn't get THAT scope with the express intention of enjoying a half-cocked image, did you now... :question::question:

If you have an SCT or a Skywatcher Mak, collimating is very easy, but it is time consuming, and in our rush-rush-rush lifestyles this isn't the most enjoyable experience. BUT, get the optics right, and oh-golly-gosh! you are in for a treat tonight! :D What makes the collimating experience worse is the pressure you put on yourself to get to use the scope viewing through it! It's an unfair pressure and it is all self inflicted. But it's something you need to control. Or do you still want that half-cocked image...?

I'll give you a recent example of mine. I borrowed an 8" SCT from a mate last month. It's about 8 years old, and a stock standard SCT. When I set it up the image was "ok". Saturn was nice with this scope, the Cassini Division was clear, and the cloud bands were noticeable with shading differences, but I did notice that the optics needed tweaking. So I spent some time tweaking the secondary mirror's collimation screws, and spent half an hour slowly tweaking this screw this way, same screw the other way a bit less, tweaking another just a touch, etc. When I got it as good as I could, OMG! WHAT A FLAMING DIFFERENCE!!!

The cloud bands were now able to be seen individually, not just as a difference in shading. The Cassini Division was so sharp. There was such a distinct difference between the A, B & C rings in hue, and the C ring hinted at shading differences. Oh, and the kicker was the Encke Division was now visible! :D :D :D

Was it worth that half hour to tweak the "ok" image? You bet!!!

With a Newt or a high end Mak like an Intes Mak, you have to adjust both a secondary and primary set of mirrors, and it doesn't take that long either. You just cannot rush it. I adjust my Newts every time I set them up because these scopes have a lot of subtly held moving parts that they do shift a little with the vibrations of transport - it's one of the hazards of owning a Newt.

Yes, at first I found it a pain in the bum to collimate, but now it is part of my set-up ritual and not something I would ignore doing as I know it is to MY benefit.

The good thing about Maks and SCTs is they hold their collimation a whole lot better than Newts, so tweaking them is a rare event. But SO MUCH WORTH THE EFFORT! :D

Alex.

[Outcast]

:eyepop::lol:

I will give it a go... but, first some careful reading to try & understand the process & not screw it up completely...

[morls]

Well, you've convinced me Alex. I'm throwing caution to the wind and getting out the power tools..:work: :work:


Seriously though, you're 100% correct, it's the best way to learn. I'll start with some daylight collimation and hopefully the skies will be clear again soon so I can use the star test to get it spot on.


And the daytime work means I can get to know the layout without fumbling around in the dark.


Thanks
Stephen

[TareqPhoto]

Right, so my Mak need collimation or tweaking because people say so, you are right, all my results are really not good at all, such as those 2 under poor seeing condition

https://i.postimg.cc/9ccTr3Qj/03-03-16-lapl3-ap193.jpg


https://i.postimg.cc/1sNb2mTd/04-18-00-lapl3-ap172.jpg


I can show planets too, so i don't know how to collimate it to get any better.

[Saturnine]

Tareq

If your Mak is giving you images that crisp I wouldn't be in a hurry to muck around with the collimation.

[TareqPhoto]

Those are from my Mak definitely, under poor seeing as i said i didn't process it even much further, so do you really think i should do that because all who got this Mak want to collimate it?

[Saturnine]

The collimation could possibly be improved but the images suggest that it is good already. Have you performed a star test with it to see if the shadow of the secondary in a defocused star is concentric with the disc of the the defocused star, using a high power eyepiece giving about 300X magnification.
If it is concentric then I would leave well enough alone, for the time being. Use the scope for several months at least, in all seeing conditions , to get a better knowledge of how the scope performs , before fiddling with the collimation.
I used to have a 180 Skywatcher Mak and never needed to adjust it, worked fine straight out of the box, given an hour or so, time to cool to ambient temperatures.
Regret selling it now.

[TareqPhoto]

For me, better thing is to see images or results from this Mak when not collimated and then collimated for same target in the same night, just to make sure what i am expecting, i really don't know how good or bad even in all conditions, many liked my moon shots, and my planets aren't that bad yet but i am still not satisfied with my planetary results, but i don't that the Mak will be super for the moon and in the same night it is a junk for planets, collimation shouldn't change like this, and then again another nights the moon is still nice in results but planets are just ok or so so, but as you said, i will not tocuh collimation yet.


https://i.postimg.cc/9fRSGq6N/Saturn-27-March-2018.jpg


https://i.postimg.cc/BvVRhmQx/00-02-38-lapl4-ap3.jpg


https://i.postimg.cc/tCkJgMRm/23-23-15-lapl3-ap6.jpg

[mental4astro]

Tareq,

As Jeff said, the quality of those photos certainly suggests your scope is very well collimated. But a star test is always a good way to shake up the scope to make sure it is performing at its very best. Like I said, you can settle for "good enough", or you may want to make sure that your scope is performing at its very best or if a little tweak is needed.

From your photographs, keep this in mind - there is a very different image scale being used with the Moon and the planets! The Moon shots look sharper because the image scale is small. The planets are softer because there is a lot more magnification being used. This can make things very misleading unless you are comparing images ALL at the same scale, otherwise it is a useless comparison.

Certainly don't collimate just because "people say so". YOU need to check things out for yourself, and ONLY act if you see a need to improve things. And if you find out that there is no more room for improvement with the collimation of your scope, then don't touch the blooming thing! :)

And star testing really needs to be done under good seeing conditions. Especially when really pushing the scope to its very, very best. You really do need steady seeing in order to be sure of the star figure the scope is throwing up, and any shimmering, boiling movement is not helpful.

A star test is what will tell you if you do need to tweak the collimation or not. Not me or anyone else :)

Alex.

[TareqPhoto]

Just wanted to say that i am very happy with this Mak for the moon only, but not for planetary, because of scaling, but this is no surprise, most big names are using large scopes anyway to sampling for planets, so i won't just use this Mak for everything for ever.


I did a test video on a star, focus out in both directions, and people told me that it is fine, so i just stopped there and didn't bother with collimation as long it is fine.

[morls]

Today I collimated the scope, first with naked eye/daylight and then a fine-tune with a star. It's made a real difference, and I'm very happy. It was not difficult at all, I just took my time and adjusted one screw at a time so I could see what was happening.


I noticed that the locking nuts weren't very tight at all when I started, and that care needs to be taken when tightening them after collimation. I did this at 338x magnification, and got them nice and snug. The image shift has reduced considerably, and the focus is much more positive.


Thanks everyone for your input. There's been a significant improvement already, and I'm sure I'll get better at it with practice.



Cheers


Stephen