33 replies to this topic

[Vic Menard]

...Some of us remember when collimation was done with a star and your usual eyepieces.  Even though the Cheshire eyepiece,  was described in the 20s but did not come into wide spread use beginning in the late 80's.

If I recall correctly, the original Cheshire eyepiece was intended as a collimating tool for refractors. Tectron Telescopes included the first Cheshire intended for Newtonian telescopes in 1988, along with a sight tube and an autocollimator--and a primary mirror center marker.

 

...And we got very good results with our antediluvian methods.  Some of us still do from time to time...I remember when I brought home the boxes that became my first Meade 826.  The manual had about 16 pages or so the majority of them showing how to assemble the scope.  Collimation was one or two drawings and minimal text at the back.

An 8-inch f/6 should pretty much collimate itself (and one drawing should suffice). Seriously, if you know what you're looking at you should be able to "eyeball" the collimation (a peep sight or a collimation cap would still be useful). 

 

...Nowadays I get wry looks from people at star parties who ask me where my laser is and get the "I think it is in the car, why?" answer.  

A good thin beam laser is an elegant collimation tool. A little humidity in the air clearly reveals the focuser axis (the outgoing beam) and the primary mirror axis (the return beam)--no drawings are necessary. Your scope doesn't need one, but if you had a good one to use, I bet you would like it.

 

...Though collimation is important for decent performance, some folks sort of fetishize it.

In my "limited" experience, collimation often gets the "blame" when the problem is something entirely different--bad seeing, warm mirrors, pinched optics, diffraction issues...the list goes on and on. Basic Newtonian collimation is a 3-step procedure. Most of the angst I see in these forums is brought on by a lack of basic knowledge, and once the user understands this basic knowledge and the 3-step procedure, the angst is significantly lessened.

 

If you want to see real collimation obsession, try following the small imaging Newtonian group (6-inches or less), with fast focal ratios (f/3.8 or less), equipped with a full size sensors and pixels smaller than 2 microns--I call it collimation insanity, but their images look, incredibly, amazing!   

[Spile]

I’ve used and can recommend the Celestron and the rather attractive Stella Lyra Cheshire Eyepiece and Sight Tube Combination tool. As for a guide then feel free to take a look at mine https://astro.catshi...limation-guide/

[star acres]

Just keep one thing in mind. There are a whole bunch of tricks and gadgets to collimate. I don't understand why someone says I leave my little telescope outside. Just take your time and don't force any screws or strain a mirror.

[dnrmilspec]

Well Vic, I have and use very good lasers when the spirit moves me.  More on my fast Newts.  My point was that I did not want to leave the impression that expensive tools are strictly necessary for useful collimation. I will leave AP issues to the appropriate forums.

[Vic Menard]

Well Vic, I have and use very good lasers when the spirit moves me.

Have you been able to discern the axes on a high humidity night? I almost asked a friend who smokes to blow a little smoke down the OTA to show the effect on a particularly dry evening.

 

...More on my fast Newts.

It's one of the tools I use on my fast Newt too. 

 

...My point was that I did not want to leave the impression that expensive tools are strictly necessary for useful collimation.

I agree, except that in some instances "expensive" and/or "complicated" tools are not "necessary" at all.

 

Considering the past few decades, it's remarkable that there are so many reasonably priced tools available today. In the late 1980's, Bob Nederman of Astronomical Innovations was selling the first commercially available thin beam laser collimator at the Texas Star Party--the going price was $350. You could also buy an accessory "bearing" that could be fitted to the laser and inserted in the focuser. This accessory allowed the laser to be tilted and rotated in precise circles, clearly showing the alignments of the secondary and primary mirrors. I seem to recall the "bearing" was a $150 accessory. The laser (and bearing) was well designed and executed, but it seemed cost prohibitive and unnecessary (to me) when I already had a 3-tool Tectron collimation set. 

 

That said, it's often easier to practice assessing and correcting the various alignment signatures with a forgiving Newtonian--one with a real spider/secondary holder and enough aperture to make it easy to reach inside the front of the OTA and make whatever mechanical adjustments are necessary--kind of a practice scope. Too may beginners start with a fast focal ratio Newtonian where offset is predictably visible (and confusing) and precision axial alignment is critical for optimal high magnification performance. These days, with the exception of a few of the available 8-inch f/6 Newtonains, it's difficult to find a (properly configured, easy to align) good slow focal ratio Newtonian. 

 

Of course, 2-inch tools are generally more expensive than 1.25-inch tools (that can also be used in a 2-inch focuser with a good 2- to 1.25-inch adapter, like a Parallizer). There are also some tools (2-inch and 1.25-inch) that will simply not work "as advertised" for a given Newtonian configuration, and other tools that can actually be adjusted for almost any configuration. We try to provide collimation guidance in these forums--sometimes we're too late, sometimes a beginner is simply shopping for the least expensive tool (they all "look" the same) or a "no-tool" collimation method, and sometimes a beginner just gives up (...I can see more with my 4-inch f/6.5 refractor than my 8-inch f/6 Newtonian).

 

I've learned along the way, while we've come a long way making Newtonian collimation accessible and comprehensible, that you still can't win 'em all.  

Edited by Vic Menard, 27 June 2025 - 10:10 AM.

[Oldfracguy]

Adding this thought.

 

Some of us remember when collimation was done with a star and your usual eyepieces.  Even though the Cheshire eyepiece,  was described in the 20s but did not come into wide spread use beginning in the late 80's.

 

And we got very good results with our antediluvian methods.  Some of us still do from time to time.

 

Though collimation is important for decent performance, some folks sort of fetishize it.  I do not haul out all of my lethal accessories every time I use my Newtonian scopes.  I am content to tweak stuff with a nice star and enjoy looking at stuff. 

 

 

Nowadays I get wry looks from people at star parties who ask me where my laser is and get the "I think it is in the car, why?" answer.  

 

Well Vic, I have and use very good lasers when the spirit moves me.  More on my fast Newts.  My point was that I did not want to leave the impression that expensive tools are strictly necessary for useful collimation. I will leave AP issues to the appropriate forums.

I use a simple Cheshire with crosshairs to collimate (fairly infrequently I might add) this 6" f/6:

 

 

 

and use a real star to finish off the final adjustment.  Normally I use a 5mm eyepiece to do this.  The other night, even without adjusting the primary mirror screws, the collimation still looked fine, with perhaps just a tad of misalignment not enough to worry about at all, in a 3mm DeLite for 300x.  

 

Excellent collimation results can be obtained using a real star once the secondary mirror has been properly positioned beforehand using other techniques involving a Collimation Cap, Cheshire or Laser.

Edited by Oldfracguy, 27 June 2025 - 09:39 PM.

[Vic Menard]

I use a simple Cheshire with crosshairs to collimate (fairly infrequently I might add) this 6" f/6: and use a real star to finish off the final adjustment.  Normally I use a 5mm eyepiece to do this.  The other night, even without adjusting the primary mirror screws, the collimation still looked fine, with perhaps just a tad of misalignment not enough to worry about at all, in a 3mm DeLite for 300x. 

Interesting. At f/6, the coma "free" field diameter (where coma is less than 1/4-wave) is 4.75mm. TeleVue's eyepiece specification page shows the DeLite 3mm has a 3.2mm fieldstop. As long as your Cheshire alignment error is less than about 1mm, the entire field of view should be coma "free" in the 3mm DeLite. Of course, the primary mirror center mark positioning also affects the alignment read, but the errors are vectors that are rarely perfectly aligned to the "worst case scenario", but I guess it's possible. 

 

https://www.televue....=214&plain=TRUE

 

Were you using Mike Lockwood's star alignment method?

 

https://www.loptics..../starshape.html

Edited by Vic Menard, 28 June 2025 - 12:15 PM.

[Oldfracguy]

Interesting. At f/6, the coma "free" field diameter (where coma is less than 1/4-wave) is 4.75mm. TeleVue's eyepiece specification page shows the DeLite 3mm has a 3.2mm fieldstop. As long as your Cheshire alignment error is less than about 1mm, the entire field of view should be coma "free" in the 3mm DeLite. Of course, the primary mirror center mark positioning also affects the alignment read, but the errors are vectors that are rarely perfectly aligned to the "worst case scenario", but I guess it's possible. 

 

https://www.televue....=214&plain=TRUE

 

Were you using Mike Lockwood's star alignment method?

 

https://www.loptics..../starshape.html

No, I wasn't using Mike Lockwood's method at all.  I just use the same technique I use with Maks and SCTs.  I don't go by Suiter's recommendation to use an eyepiece that has a focal length in millimeters equal to the focal ratio of the scope , or 25x per inch of aperyture.  I like to use one the next size down.  For example, in an f/6 scope I would select a 5mm eyepiece; in an f/10 SCT a 9mm or 8mm eyepiece; and in an f/15 Mak a 12mm eyepiece.  I can see the diffraction rings better, and then judge if they appear to be crunched up on one side of the dark central shadow and stretched apart a little on the other side.  Then I start adjusting the primary mirror screws (or the secondary mirror screws on the front of an SCT) to get the diffraction rings to be concentric with equal spacing between them all around.  If I see that when defocusing the same amount on both side of focus then I consider the scope to be collimated and ready for use.

 

On scopes like Maks that can easily do 50x per inch and higher I'll stick in a shorter focal length eyepiece and only defocus just slightly so that I can see the bright dot in the center of the diffraction pattern.  Then I finish adjusting the collimation screws, or perhaps just one, until the bright dot is centered withing the innermost diffraction ring just off focus.

[Vic Menard]

1.) ...I just use the same technique I use with Maks and SCTs. 

2.) I don't go by Suiter's recommendation to use an eyepiece that has a focal length in millimeters equal to the focal ratio of the scope , or 25x per inch of aperyture.  I like to use one the next size down.

3.) ...I can see the diffraction rings better, and then judge if they appear to be crunched up on one side of the dark central shadow and stretched apart a little on the other side. 

 

4.) ...On scopes like Maks that can easily do 50x per inch and higher I'll stick in a shorter focal length eyepiece and only defocus just slightly so that I can see the bright dot in the center of the diffraction pattern. 

5.) Then I finish adjusting the collimation screws, or perhaps just one, until the bright dot is centered within the innermost diffraction ring just off focus.

1.) SCTs and Maks don't have an offset secondary mirror, which can make the Newtonian read a bit more complicated at f/5 and shorter. (At f/8 they're very similar.)

2.) I think 25X per inch of aperture can be useful if the seeing and your visual acuity are very good. I find 50X per inch of aperture more useful even though my local seeing is usually quite good. My visual acuity is not what it used to be 50 or 60 years ago. (I can still use 25X per inch of aperture (550X) with Mike Lockwood's method.)

3.) I try to keep the Airy disk visible with one or two diffraction rings on my 6-inch f/8 scopes (refractor and Newts). That said, my star alignment read has always verified my Cheshire alignment.

4.) This is where I do all of my fine star alignment.  

5.) Yes!