21 replies to this topic

[iluxo]

This procedure describes how to collimate a maksutov-newtonian telescope such as those from Skywatcher, Explore-Scientific, APM, Intes or Intes-Micro. The same procedure applies to conventional Newtonians as well, apart from the corrector plate.

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[DaveDE]

Nice article. Now if only Howie Glatter laser collimators were available.

[Bob Campbell]

Excellent article. While I now only have SCTs and refractors, I do enjoy (reading about, not doing  ) the meticulous process of collimating a Newtonian class scope. Reminds me of my time with a TAL-150P and a Cave 10" F6 Astrola.

 

One question though. You (The author) were last active 2014. How did this get posted, anyway?

 

Edit: someone by the name of bondiblue posted it, apparently, however a scan for that member comes up empty. Odd, but nothing to bother oneself about.

 

Regards,

 

Bob

Edited by Bob Campbell, 01 March 2023 - 10:04 AM.

[GoldSpider]

I've long suspected my mak-newt's meniscus wasn't square to the primary mirror; something that wouldn't show up when collimating such a scope like a regular newtonian (as explained in Figure 2.)  What's the best way to make sure the corrector is square to the primary mirror?

[TG]

It takes some time to realize that Mak-Newtonian collimation is not the same as Newtonian collimation. In a plain vanilla Newtonian, the aperture stop is at the primary mirror. One can use whatever means of collimation that might also require tilting the focuser, resulting in the optical axis not being parallel to the tube axis. This results in no optical effects but if digital encoders are being used, you might have to account for this in the pointing software. In contrast, the aperture stop in the Mak-Newt is at the corrector and the optical axis is required to be square to the corrector's axis otherwise you get astigmatism and/or coma. While the primary is spherical with no preferred axis, due to a lack of lateral adjustments, it also needs to be physically square to the corrector axis. Any collimation method must preserve this fact. This is the crux of the problem with Mak Newt collimation.

[luxo II]

... might also require tilting the focuser, resulting in the optical axis not being parallel to the tube axis. ...

If thats the case the focuser is misplaced along the OTA as in figure 2. Fix that and there should be no need to tilt the focuser. 

[luxo II]

I've long suspected my mak-newt's meniscus wasn't square to the primary mirror...

More likely your diagonal is tilted. If the corrector was tilted that will introduce a whole class of issues that collimating the mirrors cannot fix.

 

In 25 years none of the MN's I've seen suffer from this... but admittedly they were all Russian with machined tubes.

[mayhem13]

It takes some time to realize that Mak-Newtonian collimation is not the same as Newtonian collimation. In a plain vanilla Newtonian, the aperture stop is at the primary mirror. One can use whatever means of collimation that might also require tilting the focuser, resulting in the optical axis not being parallel to the tube axis. This results in no optical effects but if digital encoders are being used, you might have to account for this in the pointing software. In contrast, the aperture stop in the Mak-Newt is at the corrector and the optical axis is required to be square to the corrector's axis otherwise you get astigmatism and/or coma. While the primary is spherical with no preferred axis, due to a lack of lateral adjustments, it also needs to be physically square to the corrector axis. Any collimation method must preserve this fact. This is the crux of the problem with Mak Newt collimation.

Aaaaagh…that makes sense……I never considered that before. Thanks for sharing. I just ordered the Skywatcher 190mn this week. I only have a Farpoint laser so I guess I’m going to need the Glatter setup if this is comes outta whack out of the box.

[PartlyCloudy]

I hate to say this, but can you even get these H-G Collimator lasers?  Even on their website, they indicate very extended lead times, and I have not seen one in stock or heard of anyone getting one for a very long time.  Years in fact (and I have looked regularly and even send emails to the company, never returned).  So many Youtube and other collimation resources list them as the ones to purchase, yet there are none.

[Bob Campbell]

I hate to say this, but can you even get these H-G Collimator lasers?  Even on their website, they indicate very extended lead times, and I have not seen one in stock or heard of anyone getting one for a very long time.  Years in fact (and I have looked regularly and even send emails to the company, never returned).  So many Youtube and other collimation resources list them as the ones to purchase, yet there are none.

Will the procedure not work if a laser collimator other than the HG is used?

 

If it is the holographic circles, there can be an addon for other laser collimators.

 

Quick search yields:

 

https://www.starligh...hic-collimator/

 

 

Bob

Edited by Bob Campbell, 03 March 2023 - 12:23 AM.

[luxo II]

Bob great find that’s the holographic attachment.

 

These have a threaded stud which screws into the Glatter collimator but there’s nothing wrong with using other laser collimators like the Farpoint one - though you have to find a way to attach it to the collimator and not lose it inside the scope. A little Blutack would do.

 

NB having experimented with mine I can confirm there is nothing critical about centring or tilt, you can put it on backwards… the hologram showed no shift or other effects. What DOES matter though is making sure the laser is accurately coaxial with the body of the collimator and adjusting accordingly if not.

Edited by luxo II, 03 March 2023 - 12:54 AM.

[rigelsys]

It takes some time to realize that Mak-Newtonian collimation is not the same as Newtonian collimation. In a plain vanilla Newtonian, the aperture stop is at the primary mirror. One can use whatever means of collimation that might also require tilting the focuser, resulting in the optical axis not being parallel to the tube axis. This results in no optical effects but if digital encoders are being used, you might have to account for this in the pointing software. In contrast, the aperture stop in the Mak-Newt is at the corrector and the optical axis is required to be square to the corrector's axis otherwise you get astigmatism and/or coma. While the primary is spherical with no preferred axis, due to a lack of lateral adjustments, it also needs to be physically square to the corrector axis. Any collimation method must preserve this fact. This is the crux of the problem with Mak Newt collimation.

Corrector "square on" to the optical axis -- yep I've been discussing this on this thread about  SCTs and MAKs collimation 

 

https://www.cloudyni...age-2?hl= aline

 

"The wifi-Aline is very helpful in checking that the focus tube, secondary and primary are not grossly misaligned causing vignetting. Given the nature of spherical mirrors used in SCTs and MAKs the secondary can be tilted and still seen as mechanically centered in the primary.

For SCTs and MAKs collimation requires the refractive component (The aspheric corrector plate in an SCT or the spheric corrector plate in a MAK) also be “square on” (not tilted with respect to the spherical primary and secondary optical axis) otherwise one side of the corrector plate will “correct” short and the other side “correct “long, producing aberration in the focused the star image.

As a consequence, collimating the corrector plate to the primary-secondary optical axis in SCTs and MAKs is best done by star testing. It is quick, simple, and requires no additional gear beyond a tool to adjust the secondary screws on an SCT or primary screws on a MAK."

 

​So using a laser will help put the optical axis into collimation (focuser, secondary, primary) but not put the optical axis "square on" to the corrector plate.

 

So I'm going to hypothesize, after roughing in the finder, secondary, primary optical axis to minimize vignetting,  star testing for "square on" to the corrector plate just requires adjusting just the primary tilt as in a classical MAK?  Will be interesting to see how one adjusts a Mak Newt optical axis to be "square on" to the corrector :-)

[GoldSpider]

Would a corrector not square to the primary account for the scope appearing to be collimated on one side of focus and not the other?

[luxo II]

No it wouldn’t. What it would do though is introduce a noticeable spherical aberration which on one side of the focal plane appears overcorrected and on the other under-corrected, resembling astigmatism.

[rakrok]

What would cause the scope to appear collimated on one side of focus but not on the other? I have this issue right now with a Mak and I'm unsure how to fix it.

[rigelsys]

No it wouldn’t. What it would do though is introduce a noticeable spherical aberration which on one side of the focal plane appears overcorrected and on the other under-corrected, resembling astigmatism.

I think this is the closest answer, the primary (or corrector plate) is over/under corrected.  I found these kind words.

 

"Spherical Abberations
Another problem frequently encountered is spherical abberation. This is when the outer parts of the lens or mirror don't quite have the same focus as the center parts. Cheap telescopes often suffer from spherical abberation and it makes viewing faint objects quite difficult and can make pin sharp views impossible.There are two types of spherical aberration, under-corrected and over-corrected.

 

If you have over-correction the concentric rings inside focus will not be sharp, yet the outside focus will be. If the inside focus is sharp and the outside focus is blurry then you have under-correction.

 

If the outermost ring has spikes or streaks it indicates that the mirror may have a turned down edge. The methods for fixing these abberations, or if they are even possible to fix, depends on the type of telescope you have any the amount of adjustability it offers. You should check your handbook that came with the 'scope."

Edited by rigelsys, 14 March 2023 - 05:09 PM.

[luxo II]

Hmmm… I mean left/right sides of the focal plane not inside/outside - the question was what’s the consequence of a tilt of the corrector - not under/over correction.

Might be interesting to try…

[Vic Menard]

This procedure describes how to collimate a maksutov-newtonian telescope such as those from Skywatcher, Explore-Scientific, APM, Intes or Intes-Micro. The same procedure applies to conventional Newtonians as well, apart from the corrector plate.

I've always looked at the alignment of the Mak-Newt corrector surface to the surface of the primary the same way you would look at the alignment of the surfaces of an air-spaced achromat, where thin shims are often used to keep the surfaces in the correct alignment (obviously, the air-space is significantly larger in the Mak-Newt). This is the critical alignment for Mak-Newt optical performance, so these axes must be maintained.

 

On first read, your procedure seems to be valid, and provides correction for each element (given a fixed meniscus). If it works for imaging scopes with large sensors and small pixels, that should be enough to keep your readers happy! If it doesn't work, it probably means a meniscus/primary error that will require some sort of bench autocollimation, probably with a large optical flat.

 

I'm not sure of your math re: secondary offset and actual offset of the laser rings relative to the secondary shadow.

 

For secondary offset, you suggest (1.41 X d)/(4 X f), which represents the offset on the surface of the secondary mirror (the hypotenuse). The lateral offset away from the focuser side of the tube assembly is d/(4 X f). For a 48mm minor axis secondary mirror and an f/6 primary mirror, the offset is 2mm.

 

For the actual offset (laser rings relative to the secondary shadow), you suggest averaging the opposing inner gaps (o1 + o2)/2. This provides the correction for a centered secondary mirror shadow (o1 = o2). For an o1 of 6mm and an o2 of 2mm, the average is 4mm. For the actual offset, subtract the average from the measurement opposite the focuser side of the tube assembly, in this case, o1 is 6mm, the average is 4mm, and the actual offset is 2mm.

[Parks51998]

Howie Glatter laser collimators backordered on High Point.

[unimatrix0]

Howie Glatter laser collimators backordered on High Point.

For about the past 3 years. I've been checking on it. 

[TG]

For about the past 3 years. I've been checking on it. 

Given that Howie passed away some time ago, who's making them now?

[Hockeyman65]

Attached is Messier 106 

 

I own the Sl-LC2-635-NV with the concentric circle attachment . Best purchase I have made to date. This unit can get you very close to a final adjustment. Used in conjunction with PHD2 and a Bahtinov Mask . You can reach collimation very easily and quickly.

 

The photo attached was taken after only one collimation session of about an half hour the first night.

Oh yes Bobs Knobs were involved too  .

 

Here is the equipment and process used:

 

Meade 12" GPS mounted on a JTW Astronomy Trident Friction mount. Using a Nikon D5100 on an Optec TSFs focuser  . About 14 hours of integration time and over 1700 30 second images.

 

Sequenced in NINA and processed in Siril

 

So this collimation tool is a must in anyone's repertoire.

 

So for a rebuilt older Meade I think it came out ok.

 

Scott

 

Edited by Hockeyman65, 24 March 2023 - 12:09 PM.