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Old 08-01-2020, 09:53 PM
Startrek (Martin)
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Collimating Newtonian Reflectors

Using only Newtonian reflectors for both visual astronomy and Astrophotography over the past 3 years, I’m interested to know how many beginner visual astronomers and beginner astrophotographers chose to buy a small to medium refractor telescope as their first telescope in lieu of considering a Newtonian reflectors merely on the basis of being concerned or worried about how to “collimate” or that collimation could be an arduous task that needed to be done all the time , or even limited understanding about the process ??
I noticed flicking through posts on other forums like CN and SGL that “collimation” seemed to be one of the key factors that determined their decision to go refractor.

I welcome comments from beginner visual astronomers and beginner astrophotographers on the above topic
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Old 08-01-2020, 10:32 PM
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Outcast (Carlton)
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Originally Posted by Startrek View Post
Using only Newtonian reflectors for both visual astronomy and Astrophotography over the past 3 years, I’m interested to know how many beginner visual astronomers and beginner astrophotographers chose to buy a small to medium refractor telescope as their first telescope in lieu of considering a Newtonian reflectors merely on the basis of being concerned or worried about how to “collimate” or that collimation could be an arduous task that needed to be done all the time , or even limited understanding about the process ??
I noticed flicking through posts on other forums like CN and SGL that “collimation” seemed to be one of the key factors that determined their decision to go refractor.

I welcome comments from beginner visual astronomers and beginner astrophotographers on the above topic
I'll take the bait...

Yes, I bought a refractor for my first scope but, not because of collimation.. not sure I even knew what that was when I started out..

I bought a refractor after weighing up other considerations such as portability & weight.. whilst I would have liked an 8" dob, I didn't feel I would use it because of it's size & weight...

Fast forward 11 years, my first experience with collimation was actually with an 8" SCT.. yep, I was worried about how hard it might be but, after obtaining good advice, I took the plunge & as long as you are methodical & patient & make small changes between looking at the results; it really ain't that hard...

I now own two Newtonians, only bought them this year.. again I had to confront that 'huge' bogey man that seems to be collimation.. yet again, I sought advice, did some reading & hey presto, after a bit of thought to understand the mechanics of what I was doing (I will point out here, I don't have a mechanically minded cell in my brain), I gave it a crack.. each time I do it, (my Dob is a custom truss, it get's pulled down between uses so, generally needs a small tweak when setup) it becomes more simple & so much more instinctive...

If you are avoiding a Newtonian purely because of 'collimation', then my advice as a newby to Newtonians, is don't... it's really not that hard...
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Old 08-01-2020, 11:09 PM
gaseous (Patrick)
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I'd rather collimate a dob than try to get a polar alignment on a refractor (or similar). I feel for the people who have to do both, but if you're going down the photography path, you deserve a bit of pain Collimating a dob should only take a few minutes, max.
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Old 08-01-2020, 11:46 PM
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I'd rather collimate a dob than try to get a polar alignment on a refractor (or similar). I feel for the people who have to do both, but if you're going down the photography path, you deserve a bit of pain Collimating a dob should only take a few minutes, max.
Polar alignment isn't as hard as people make out either just quietly... it's just like collimation, it's a process & with the software already onboard most modern EQ mounts, it's actually a bit of a doddle...
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Old 09-01-2020, 05:31 AM
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mental4astro (Alexander)
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Martin et al,

I'm not a newbie, but on reflection on my own experiences over the years with your question, I hope to allay some fears people may have about refractors vs reflectors (of whatever type).

I have come to see that there are two main reasons for why people take up refractors over Newtonians (or any other type of reflector such as SCT or Mak) when they start out in astro:

* the word "collimation"

* a Newtonian "does not look like a telescope".

Collimation ONLY MEANS aligning the optics. That's it. Nothing more. And sadly seeing all the weird diagrams, gizmos and even lasers to do with collimating, and people become fearful of Newts and cassergrains

That Newts don't look like a telescope stems from most people's only association with any form of telescope is a refractor, yes, that pirates use! Sadly many people's initial knowledge of astronomy and telescopes is entirely set on what pirate's use, and that the gear that professional astronomers use is somehow tantamount to unfathomable "rocket science"... Heck, I even had the Spooks called on me a few years back when setting up a truss dob, and another time a fellow became very pissed off & aggressive with me when he refused to believe that the 5" SCT was showing him Saturn...

I see the confusion and scepticism in many novices at outreach events when they see my Newts or cassegrains as being telescopes instead of a refractor. Not helping the situation for dobs is the odd looking mount instead of a tripod and rocket science equatorial mount. I've also encountered this ignorance when organizing outreach events when the non-astro people I had to work with thought that the scopes we were bringing were hand-held "priate" style telescopes - I kid you not! In one instance these were National Parks rangers



As Carlton said, there really is nothing mysterious or rocket-science about "collimation". It is only tweaking a couple of mirrors to optimise the effectiveness of the scope, it only takes moments, and if you take the time you will get the scope humming at its very best for you with a larger aperture than a refractor can offer for the same price. What refractors do have over reflectors is they typically don't require tweaking of the optics. The inconvenience that some people perceive that the collimation process introduces or the optical artifacts that reflectors can introduce to the image is a factor, but less so.

As for Newtonians and cassegrains (both solid tube and truss designs) not looking like a telescope, I reckon by now your thinking would have changed.

Alex.
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Old 09-01-2020, 09:58 AM
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Quote:
Originally Posted by Startrek View Post
Using only Newtonian reflectors for both visual astronomy and Astrophotography over the past 3 years, I’m interested to know how many beginner visual astronomers and beginner astrophotographers chose to buy a small to medium refractor telescope as their first telescope in lieu of considering a Newtonian reflectors merely on the basis of being concerned or worried about how to “collimate”
Quote:
Originally Posted by Outcast View Post
I bought a refractor after weighing up other considerations such as portability & weight.. whilst I would have liked an 8" dob, I didn't feel I would use it because of it's size & weight...
In my case, I bought a Newt on a tabletop Dobsonian mount, for very similar reasons to why Outcast chose his first refractor. Size, portability, and weight.
In doing the research to build my short list of scopes to actually examine in store, I'd read about needing to do collimation on Newts and the prospect of needing to do that, didn't worry me at all.
One look at the physical footprint needed for the tripod from the SkyWatcher AZ3 mount 80x400, and 70x900 refractor sets, made it clear that the tripod for neither telescope would fit on my patio/balcony. Added to that, the physical length of the 70x900 would, quite simply be too long to use.
So the refractors were scrubbed from my list immediately.
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Old 09-01-2020, 11:04 AM
Startrek (Martin)
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Thanks all for your comments , great stories and feedback
Hope more people respond as it’s an interesting topic and one that may open some doors for newbies considering to buy their first telescope.
Alex , an excellent report ,hits the nail on the head. Your comments and explanation dispels any concerns or myths people have about the process of “Collimation”
I found one important upgrade on my 6” and 8” newts that made collimation so much easier and that was to replace my existing cheap chinese primary mirror springs with locally made high quality springs ( Better Springs in Sydney ) Made all the difference in the world, my scopes stay in good collimation even being removed and re installed on their mounts , a quick 1 minute check with a laser and done !!
Thanks all and welcome more interesting stories and experiences
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Old 09-01-2020, 12:39 PM
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I found one important upgrade on my 6” and 8” newts that made collimation so much easier and that was to replace my existing cheap chinese primary mirror springs with locally made high quality springs ( Better Springs in Sydney )
I'm looking at replacing the springs on my Vixen R130SF, what type (metal type) springs did you replace the OEM ones with?

How critical to match diameter & length exactly?

Cheers
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Old 09-01-2020, 02:42 PM
bgilbert (Barry gilbert)
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. One off the significant differences between refractors and newtonians is the point spread function (PSF) or the Airy ring structure. The central obstruction in the newt increases the amplitude of the Airy rings at the expense of the central peak. The net result is bigger stars and less planetary detail for for any given aperture.

. If you increase the aperture of your newt 10 or 20 % you'll catch up with the refractor. Also refractors always suffer from chromatic aberration to some degree, unless you spend big bucks. Refractors need collimation, but is done in the factory and holds pretty well as long as you don't overload the focuser. I almost forgot the spikes on the newts stars caused by the spider vanes. .
. You get a lot of bang for your buck with a big newt.
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Old 09-01-2020, 02:53 PM
Startrek (Martin)
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I had my new springs made with similar ID and OD , slightly longer by 3mm but most importantly with a stronger compression rating
My old springs had weak compression and therefore collimation would be difficult to nail. Stronger springs give you more control over fine adjustment.
The new springs weren’t cheap but the difference was amazing and in hindsight I should have upgraded as soon as I bought the scope

I also cut out / fashioned / fitted a piece of plastic from a 2 Ltr milk container and placed it behind the secondary mirror mount / stalk so the 3 adjustment screws have a firm base to screw into rather than “pit” the alloy base. It also made a huge difference to the secondary mirror alignment. I found this little mod on a website demonstrating collimation.

Collimation rarely drifts in my scopes and I just do a quick check with a laser once in a while
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Old 09-01-2020, 08:33 PM
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Thanks Martin, I'll do some investigating locally but, might be in touch via PM if I draw a blank up here if that's okay?

Cheers
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Old 09-01-2020, 11:35 PM
Astronovice (Calvin)
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Cairns Spring Works

Hi Carlton

Try Cairns Spring Works, 3 Redden St, Portsmith
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Old 10-01-2020, 12:22 AM
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Collimation is realistically much more of a challenge in an F4 scope than F5 or F6. How well it holds of course depends more on scope construction.

I'm an astrophoto addict now using 4" refractor, but have never regretted starting with an 8" Newt, which don't ever plan to part with. Horses for courses, but agree people shouldn't be afraid of collimation.

Love the soft rounded stars from my refractor, but reflector stars have a charm of their own - albeit if the central part of star profiles is a bit "flat". Cost/aperture so much less for reflectors, you'll never need to be comparing a refractor with similar size Newt - the Newt will/should always be much bigger for same dollars.

Pardon colours from the older newt pic, but comparison of 4" refractor versus 8" Newt, same camera. (Refractor costs >20 times Newt )
Refractor processing could have perhaps taken more contrast in processing, and total flat FOV much larger in non-cropped full image from the refractor, but comparing similar part of image Skywatcher Newt has nothing to be ashamed of
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Old 10-01-2020, 08:20 AM
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Hi Carlton

Try Cairns Spring Works, 3 Redden St, Portsmith


Thanks Calvin
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Old 10-01-2020, 07:59 PM
Startrek (Martin)
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Carlton
Hope your local spring company can help you
My spring guy in Sydney needed my old springs to test the dimensions and compression rating. I went one step further and took the scope with me to show him the issue with the primary mirror adjustment
Although he knew nothing about astronomy he knew exactly what I was after and machined the new springs to work so much better than the original cheap and nasty Chinese springs.
I had 2 sets made up so they will outlast me
Good luck !

Back to the original post , any other comments in regard to collimation fears or apprehension when choosing your first scope ??
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Old 10-01-2020, 08:24 PM
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Quote:
Originally Posted by Startrek View Post
Using only Newtonian reflectors for both visual astronomy and Astrophotography over the past 3 years, I’m interested to know how many beginner visual astronomers and beginner astrophotographers chose to buy a small to medium refractor telescope as their first telescope in lieu of considering a Newtonian reflectors merely on the basis of being concerned or worried about how to “collimate” or that collimation could be an arduous task that needed to be done all the time , or even limited understanding about the process ??
I noticed flicking through posts on other forums like CN and SGL that “collimation” seemed to be one of the key factors that determined their decision to go refractor.

I welcome comments from beginner visual astronomers and beginner astrophotographers on the above topic


Actually collimating a "reflecting" telescope is so easy I am amazed people are concerned, with a laser collimator it takes minutes.

However remember refracting scopes also need to be either 100% accurately collimated if they don't offer collimation or also need collimating on occasions which is why higher end ones offer colimatable lens cells.
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Old 10-01-2020, 09:43 PM
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I’ve had my fair share of different telescopes though my short astrophotography journey. Starting with an entry level Mak Cas I knew nothing of collimating and couldn’t adjust it anyway. Then I moved to C5 SCT and could adjust my secondary which I found quite easy to do after watching a couple of YouTube videos. I think once you understand what it is you’re trying to achieve, it’s really not that difficult. I bought a doublet f/5 refractor and the appeal there was that at f/5 I could get so much more light faster. To this point I hadn’t had a Newt. Next came a Vixen 130rf f/5 Newt. Now I was collecting more light faster and cheaper but I did have to learn more about collimating given I was adjusting both primary and secondary mirrors. Again, really not that hard when you really understand what you are trying to achieve. Admittedly buying a laser to complement my Cheshire did help in that regard. Next came a C9.25. Again just as simple as the C5. SCTs are really quite easy but you do have to be careful with mirror flop. Finally entering my stable was an 8” f/4 imaging Newtonian and this is where things become more difficult..... at f/4 the adjustments are far more touchy and it doesn’t hold collimation quite as well. In summary I’d say there is nothing to be fearful of with Newtonians once you understand what you are trying to achieve but the faster the scope, the more time it can take to do.

Last edited by RyanJones; 10-01-2020 at 09:58 PM.
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Old 11-01-2020, 07:45 PM
Startrek (Martin)
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Ryan
Thanks for some of your history and a great summary

For those who might go down the Newtonian reflector path as a first telescope ( you won’t be disappointed) here are two great sites for collimating Newtonian reflector telescopes -

Starizona

Astrobaby

Also IIS members are always here to help

Cheers
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Old 11-01-2020, 08:37 PM
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This is from a post i made last year , just if you missed it

I bought a real Auto Collimator & now know why they work so well .

If you have ever been to a fun park were they have a hall of mirrors and you check your reflection in the mirror your looking at whilst seeing the one behind you , what do you see ? multiple reflections .

Because those mirrors have a tilt .
Now if they were perfectly aligned with no tilt You would not see your reflection ' that's what the Auto Collimator doe's .
You go from a bright reflection to a dark one when your scope is spot on !

But you will need to centre mark your secondary before this to get those earlier adjustments extra close .

After you have used your best tools ( lasers included ) to get what you think is spot on , then use the auto collimator for perfection .

Have Fun
Bobby
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