Collimating Fast Newtonians

Dear Astrobinners,

I would appreciate your wise counsel one again. I have recently purchased a TS Hypergraph 8 f3.2 Newtonian. I knew that collimation would be a challenge, but have successfully collimated my RC8 before now. So, how difficult could it be?

After eight hours during the day and a similar amount at night trying to achieve collimation with my 1.25inch TS concenter, TS Cheshire and cheap laser, I am beginning to reconsider my evaluation.

Perhaps my 1.25inch TS concenter is too small (sent in error to me my TS rather than the 2inch version) as the largest ring on the concenter is smaller than the secondary I am trying to align under the focusser.

Perhaps my TS 1.25inch Chesire is too small - very hard to get an image of the secondary.

And the less said about my laser the better. The spot disappears once it gets within the centre ring mark on the primary and the return hole is so large I can't determine the précise alignment to within at least an eight turn of a 1ry mirror screw.

Even the very best of my efforts to get thing concentric have resulted in failure when it comes to imaging across a full frame sensor. I can get half the field in good focus, but the other half is way out. CCDinspector says my collimation is good to within 6pix, which I suspect may not be good enough. It gives a tilt of a few degrees, but quite significant curvature. I don't think that the is due to the incorrect back-focal spacing, I am within 0.2mm of the manufacturers recommended distance.

Of course, I should have learned from my experience with the RC9 - collimation was achieved because of the right tool - the Takahashi collimator - and the good instruction manual with it.

So my question are

1) What equipment do more experienced owners of these fast systems use to collimate? The Farpoint Super Collimation kit looks good, but expensive. [Not compared to the telescope of course]

2) Is there a good guide - with clear diagrams - out there on the internet?

I would like to ensure my collimation is spot on first, before I go chasing other possible sources.

With thanks in advance for any help..

Hello Brian,
In my opinion you have to start with your secondary mirror. Important is that the mirrorholder is spot on in the center of the telescope. Then you can use the concenter of TS but the 2” version. This is a very time consuming task. It is nescessary that you can see the whole secondary mirror. At last you can use a laser to adjust the main mirror. But before you use the laser you will have to check if it is good calibrated. Doing so at a distance of 10 to 15 meter. Turn it around 360 degrees an when it is spot on it is ready to use.
I know it is easier said then done.
Anyway good luck Brian!

Wim.
https://youtu.be/r9bAKN_0l3s

My informed guess is that the scope is still a f/4 newtonian brought to f/3.2 by the CC. The collimation tools are cheshire, autocollimator and collimatable laser. Of the 3 the autocollimator is the more important. I'd have to fish out the collimation steps from somewhere and post them here. Saves me from spending a lot of time typing…

andrea tasselli:
My informed guess is that the scope is still a f/4 newtonian brought to f/3.2 by the CC. The collimation tools are cheshire, autocollimator and collimatable laser. Of the 3 the autocollimator is the more important. I'd have to fish out the collimation steps from somewhere and post them here. Saves me from spending a lot of time typing...

Actually it has a hyperbolic primary like a Ritchey-Chretien but the light is reflected by a tilted secondary to the focuser that sits at the front like a Newtonian. This naturally makes it more dependent on a corrector than an RC (which has much longer FL) and they probably throw in some reduction since speed is one of its primary design goals.

You could call it a rather ambitious catadioptric that is half Newt - half RC. Does not sound like collimating it is a breeze, when put that way...

I have noticed TS Optics do list "easy to collimate" and "holds collimation well, despite the extreme focal ratio" among the selling points of the smaller Hypegraph6 f/2.8, but they make no such claims about the Hypegraph8. Maybe they can recommend a procedure and tools.

Cheers,
Dimitris

PS I don't mean to disrespect that scope, if the 2,300+EUR wasn't an issue, I'd get one just for the looks, even without the impressive specs.

@Wim Bijl thanks for much for the advice. And good to hear that the TS 2inch Concenter is the way to go. I did check the collimation of the laser (using a jig I made and projecting onto a wall 5m distant. It looks good. And at least are accurate as my ability to centre the laser in the eyepiece holder. There is a bit of play, fix I can stop by using the brass compression ring, but I worry that this also pulls the laser off the optical axis.

Any thoughts?

@andrea tasselli Thanks, Andrea. Your informed guess is correct. The tool kit you recommend is exactly that in the Farpoint Super Collimation kit. Plus the concenter for the focusser/2ary alignment, I suspect this is the minimum toolkit.

@dkamen TS have been helpful up to a point. Their response has been "you can do better" and saying that 2ary alignment is really important. They did say that they would tell me how to use the 1.25inch concenter (sent in error) with the scope, but so far nothing. Perhaps I just need to phrase my questions to them a different way. And yes the scope looks great, and I yet hopeful it will perform as good as it looks, particularly with the help of my Astrobin friends. [And more money spent on kit *sigh*]
CS Brian

For my 10" F4 quattro, I use a catseye cheshire and autocollimator with hotspot a centered on the primary. I would steer clear of laser collimators as they don't nearly have the accuracy of the autocollimator and the laser itself may need collimating.
I also have the 2" concenter, which is great for centering the secondary to the focuser but I wouldn't rely on it for collimation as it doesn't have the accuracy of an autocollimator.

Jacob Heppell:
For my 10" F4 quattro, I use a catseye cheshire and autocollimator with hotspot a centered on the primary. I would steer clear of laser collimators as they don't nearly have the accuracy of the autocollimator and the laser itself may need collimating.
I also have the 2" concenter, which is great for centering the secondary to the focuser but I wouldn't rely on it for collimation as it doesn't have the accuracy of an autocollimator.

THanks, Jason. It looks like I am getting a very consistent picture here. 2inch Concenter for aligning 2ary to the focusser, Chesire/collimated laser for initial 2ary/1ary collimation and then autocollimator to complete this job.

CS Brian

Brian Boyle:
Jacob Heppell:
For my 10" F4 quattro, I use a catseye cheshire and autocollimator with hotspot a centered on the primary. I would steer clear of laser collimators as they don't nearly have the accuracy of the autocollimator and the laser itself may need collimating.
I also have the 2" concenter, which is great for centering the secondary to the focuser but I wouldn't rely on it for collimation as it doesn't have the accuracy of an autocollimator.

THanks, Jason. It looks like I am getting a very consistent picture here. 2inch Concenter for aligning 2ary to the focusser, Chesire/collimated laser for initial 2ary/1ary collimation and then autocollimator to complete this job.

CS Brian

Pretty much. The laser can help to get you in the ball park because if your a fair way off then the it's difficult to use the autocollimator as the reflections are way off center and may not be visible due to gross error. The autocollimator is great for the ultra fine tuning that the concenter and laser can't do, which is very important for fast newts.

I have the SharpStar 15028HNT and the way I collimate it is to remove the M48 to whatever (I think it is M63) adapter, then remove the corrector, then I put the adapter back on and I screw an M48 to 2" eyepiece adapter to it, then I use a Glatter with the pinpoint laser to get the secondary centered, then I use the concentric circles attachment to center the primary. Works perfectly.

I recently got a thing called an OCAL that has a camera built in, and I will check that thing out on the SharpStar. I know it worked perfectly on my Epsilon 160, so it will likely work perfectly on the SharpStar.

Either one of those methods should do what you need because both were on different fast newts.

I had good results using this procedure explained in here
https://youtu.be/8ROvNH5uwDo
Then using the laser or concenter for the last fine touch.

One more thing I've done is to tape the laser grid over and poke a little hole into it. That makes it easier to correctly align the returning laser on the grid (the beam gets a bit smaller and you see exactly the center of the grid).

Hi Brian,

I would assume that the collimation procedure of this systems isn't different from a newtonian. The mirror spacing isn't as critical as it is for an RC. Since the secondary is a plane mirror, the effect would be that your focuser position varies with mirror spacing and in extreme cases you focuser range might not suffice.

Make sure that your collimation laser is well adjusted. I once had a laser from Baader (however, purchased from TS) which was not (well) aligned. I had to do it myself in order to be able to adjust my RC.

Since you have a fast Newtonian with a modest focal length, I recommend setting up an artificial star. With that you can check the final collimation of the scope. If you can place the artificial star at 20x the FL you have a good distance. You will need some additional spacers to hold the eyepiece but as long as they aren't too many, you might be confident that you're still on the same optical path (or extremely close to it) as if you were looking at infinity.

CS!
Björn

Hi Brian,

I recommend to use a guidecam together with the little wide field lens that comes with it (at least with my little ASI120 clone) rather than the expensive OCAL.
It's the same procedure (and almost the same with the chesire), bring everything spot on an round and make use of tools like Al's Collimation or Mire de Collimation.
There are several YT vids of that procedure around. If you need assistance I'm happy to help.

Some say that the sensors of some cams are not centered as the OCAL. But I have other experience.😉

Stay safe
Mike

I can only recommend the OCAL Collimation Camera. I use it with my Epsilon 160 with very good success.
It even can show you the the factory supplied centermarks are sometimes not centered. Which I found on a friends Newtonian.

Best regards,

Stephan

my poor man's solution. Bought a cheap USB cam and printed a 1.25 adapter case. Works well enough on f4.

My biggest challenge initially with my 200mm f/4 was to make my collimation repeatable. With flex in the focuser draw tube, the primary not centralized and staying centralized in the cell and movement when tightening the thumbscrews when putting either a Cheshire or laser in. I’ve made many modifications to help and I’ve got it pretty close as far as CCDInspector says. More importantly though , it’s pretty repeatable and holds collimation pretty well.

Brian Boyle:
@Wim Bijl thanks for much for the advice. And good to hear that the TS 2inch Concenter is the way to go. I did check the collimation of the laser (using a jig I made and projecting onto a wall 5m distant. It looks good. And at least are accurate as my ability to centre the laser in the eyepiece holder. There is a bit of play, fix I can stop by using the brass compression ring, but I worry that this also pulls the laser off the optical axis.

Any thoughts?

Yes thats correct, for me it is not clear why manufactures of In this case a Newton use far to big tolerances.(the focusser) Best way to deal with this is to place the Newton horizontally with all instruments pointing up, and do not tighten to much,(You can just rotate the instruments gentle ) so the instruments will be as vertical as possible. This is really important!
Also you can blend the main mirror when adjusting the secondary.
Wim.

Hi! Seems that your scope is just like a hyperbolic astrograph. This is truly an RC scope used in prime focus with a rohss corrector. Many professional telescopes are exactly like that with the chance of use in primary focus or cassegrain focus. Your scope is too small in diameter to be used in primary focus (holding the camera with the spider instead of the secondary mirror Is not convenient due to the eccessive obstruction) so a newtonian focus Is used instead. Collimation should be done without the rohss corrector in place and it's accomplished just like a regular Newton telescope. Many times the results seems to be perfect but stars still appear to be odd, this is very often due to non perpendicularity of the imaging sensor. More than often, it Is a focuser/holder problem which Is not perfectly squared with the optical/mechanical axe. In this case You use any of the normal aids like Cheshire, autocollimator, lasers etc. but You must be sure ti act with a squared and not flexing focuser. An f3 system has a ctf (critical focus zone) of about 20/30microns so any even small flexure or mechanical irregularity could be the cause of not even stars on the field much more than a small miscollimation of the optics… These systems like the original takahashi epsilon series, are killer performers on medium fields and the real problem about is much much more related to mechanics than optics. Just keep that in mind when You experience problems on imaged fields… I do have an epsilon 210 f3 hyperbolic astrograph and It weights about 30kg! This is just due to mechanics and, even if is very old also in conception, is still a good performer on mechanical side.

Actually it has a hyperbolic primary like a Ritchey-Chretien but the light is reflected by a tilted secondary to the focuser that sits at the front like a Newtonian

Here is an excerpt from the TS blurb on the scope's page:

"TS 200 mm f/3.2 Parabolic Newtonian AstrographThe compact and portable Newtonian astrograph has been developed for the dedicated astrophotographer who wants a powerful telescope with very good sharpness over a large field of view. The astrograph has been developed for modern sensors with high resolution and large diameters up to full format.

Due to the extremely fast aperture ratio of 1:3.2, you can take very deep shots of deep-sky objects in just one night, with very high magnification at the same time. Images of extended nebula objects or galaxy clusters are thus possible.Features of the 200 mm f/3.2 Hypergraph:
♦ Parabolic primary mirror with 200 mm aperture f/3,8
♦ 3" corrector with 0.85 reduction built into the focuser
♦ 90 mm diameter secondary mirror (minor axis) for full illumination up to full format
♦ Large 3" rack and pinion focuser with reduction and M48 adapter
♦ Tilting possibility at the focuser
♦ Adjustable and stable holder for primary mirror and secondary mirror
♦ Fully illuminated and corrected image field of 44 mm diameter
♦ Working distance 55 mm from the M48x0.75 thread

"

As you can't fail to notice it says "Parabolic primary mirror". Hence no hyperbolic mirror shape and no comparison with RC's either.

D. Jung:
my poor man's solution. Bought a cheap USB cam and printed a 1.25 adapter case. Works well enough on f4.

Exactly! This is my collimation setup

Used the 2"/1.25" adapter of my laser and use it for this 8" f5 as well as for my 10" f4 with great sucess. I redo this every 6 month or so.

I have used fast Newtonians for years and after trying pretty much all the collimation tools, the best results by far have been with Catseye collimation tools. They are expensive but very well-made and deliver outstanding results when used properly. They also publish a very comprehensive manual for Newtonian collimation that will tell you WAY more than you ever wanted to know about the process but makes for excellent reference material.

Another equally critical but often overlooked detail is ensuring your imaging train absolutely nails backfocus, is orthogonal to the focal plane, and is as rigid as possible. This will take iteration, and even a 1mm change can make a material impact. Do not take the camera/filter wheel/spacer manufacturers’ guidance on backfocus at face value: measure it with a digital caliper (they’re cheap). And try a few iterations +/- 1mm from the corrector’s stated backfocus needs. Get an imaging train that bolts together if you can. And experiment with extremely minor tip/tilt adjustments if you’re able to. I’m telling you, it’s worth it, and will make a difference—at fast f-ratios, the margin for error is very small.

What wonderful advice from everyone. The consistent message is that the best tools really help. As does extreme care in the process.

For those that collimate on the bench top, I presume the collimation holds when moving it onto the mount.

It also looks like using a camera is also a good idea and I might investigate before the ZWO and OCAL solutions. Finally there is the issue of centring the tools in the eyepiece holder. I am sorry to see that many others share my experience of loose fitting collimation tools. Wow.

Anyway lots to work on and great tips. Thanks everyone so much

CS and PC (perfect collimation)

Brian

As you can't fail to notice it says "Parabolic primary mirror". Hence no hyperbolic mirror shape and no comparison with RC's either.

I'm Sorry, I have misunderestood the Word parabolic with hyperbolic... Anyway the main difference is the corrector used which, in this case, should be a wynne ti also correct the off-axis coma. The concept of CFT Is still the same and remains valid. Very important still is the absolute necessity to have a perfect squaring of the image plane to the optical-mechanical axe.

Hyperboloidal primaries do not correct for spherical aberration but they make it easier for the corrector to take care of the off-axis aberrations.

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