15 replies to this topic

[james.wheeler.pe]

I have a 305mm Newtonian.  I like the simplicity of the design.

 

Conceptually I understand collimation.  I may even be doing it correctly but would like to see some sample images from experienced people showing what the laser looks like on the main mirror and in the laser collimator just to make sure I am doing it right.

 

Here is what I see / think is correct.

 

Concern I have is on the main mirror the center mark ring picks up some glow and its not uniform around the ring.

 

Same thing in collimator... 

 

Maybe this is normal?  Maybe it identifies some issue?

 

Just would like more experienced people to confirm.

 

 

Thanks!

 

 

HoTech Laser Collimator

 

 

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[MellonLake]

That looks right to me.

I should note that I don't like the Hotech collimator. It does not register consistently in the focuser. The Farpoint or Glatter are much better.

Also, using the laser for adjusting the primary is not ideal. It would be better to use a Cheshire or Collimation cap. This is because the accuracy of aligning the secondary adds to the error adjusting the primary. If you want to use the laser you need to use the Barlow laser technique for aligning the primary.

[Jon Isaacs]

That looks right to me.

I should note that I don't like the Hotech collimator. It does not register consistently in the focuser. The Farpoint or Glatter are much better.

Also, using the laser for adjusting the primary is not ideal. It would be better to use a Cheshire or Collimation cap. This is because the accuracy of aligning the secondary adds to the error adjusting the primary. If you want to use the laser you need to use the Barlow laser technique for aligning the primary.

 

 

The Tublug was Howie Glatter's final adaptation of the Barlowed Laser.  It allows you to see the shadow of the center marker while adjusting the primary.  This is especially helpful when collimating a large scope by yourself. This is what the image looks like:

 

Uncollimated:

 

 

Collimated:

 

 

Jon

[the brook]

That looks right to me.

I should note that I don't like the Hotech collimator. It does not register consistently in the focuser. The Farpoint or Glatter are much better.

Also, using the laser for adjusting the primary is not ideal. It would be better to use a Cheshire or Collimation cap. This is because the accuracy of aligning the secondary adds to the error adjusting the primary. If you want to use the laser you need to use the Barlow laser technique for aligning the primary.

I had a Hotech collimator that I used with my 12" Skywatcher Collapsible, I would use it to align the secondary, then insert a Barlow to collimate the primary, got images like the one below with the TU Blug. I always felt that my views of the planets were superior than most of the Dobs at my clubs site

[james.wheeler.pe]

Is the Hotech really that poor?  

 

Does anyone have actual quantitative data showing the problem?

 

The design to overcome focuser registration seemed quite clever to me.

 

How would I be able to tell if focuser registration is an issue?

 

 

Jim

[MellonLake]

The critical issue in collimation is the angle of the tool to the focuser.  Centring is not that important.  Hotech designed to centre the tool which is not that critical.  The issues is the rubber rings which hold the Hotech laser in place.  These often result in tool being off axis at times and not repeatedly registering in the focuser the same way.  You can try this.  Align the secondary, take the laser out and then put it back in.  See if the laser spot moves with respect to the mirror marker.  I did this on a Hotech and found it did not repeatedly go to the same spot.  Good lasers collimators with good focusers will go back to the same spot within less than perceptible movement.  

 

Also, primary collimation is pretty critical for high magnification performance.  For your telescope assuming it is F/4, you need to have the primary aligned within 0.7mm.  As I noted earlier with the non-Barlowed technique using the target on the Hotech the secondary alignment error adds to the primary alignment error.  So if your laser is off the centre of the mirror marker by more than 0.7mm you are not going to be able to achieve good primary mirror alignment.  Using a Cheshire, Collimation Cap or the Barlowed laser technique, the reflection of the tool is used for alignment and the secondary alignment error does not add.   This is another reason the Hotech is not ideal, it is using a reflected laser rather than the reflected image of the tool for alignment.  

 

For your telescope, the allowable error for the secondary is 9.15mm with no coma corrector and 1.525mm with a coma corrector.  The primary allowable error is 0.7mm

 

Rob

[james.wheeler.pe]

Ok... got it.  Will try that experiment later this morning and share the results.

 

 

Thanks!

[james.wheeler.pe]

Well that was disappointing.

 

Guess I will be ordering the Glatter.

 

Hope I can return the HoTech.

 

 

Thanks for the feedback everyone.

[MellonLake]

Sorry to be the bearer of bad news.   

 

Rob

[briansalomon1]

Well that was disappointing.

 

Guess I will be ordering the Glatter.

 

Hope I can return the HoTech.

 

 

Thanks for the feedback everyone.

I also bought another laser collimator that truly didn't work before buying a Howie Glatter model. The Howie Glatter model I received is dead-on accurate at >20 feet from the laser aperture. I really only need it to be accurate to a little over 5 feet. (+/- 0.32mm for f4 scope with a 5' focal length)

 

I think they come standard with a 1mm removeable aperture attachment. I spent an extra $50 for a dimmer switch which reduces the brilliance so I can see >0.5mm of laser deflection. That's important if you have below an f5 mirror.

 

The Howie Glatter laser collimator is expensive, but I could have saved ~$180 if I had passed over the *other* manufacturers laser collimator and just bought this one in the first place.

Edited by briansalomon1, 24 January 2022 - 02:20 PM.

[MellonLake]

The Farpoint is also excellent and more cost effective.

 

Rob

[tloebl]

I second the Farpoint laser. Reasonable cost and very accurately collimated. 

[SteveG]

Well that was disappointing.

 

Guess I will be ordering the Glatter.

 

Hope I can return the HoTech.

 

 

Thanks for the feedback everyone.

Look at the Farpoint laser. Mine fits my focuser perfectly and is perfectly aligned. Much lower cost than Glatter.

[james.wheeler.pe]

Yes... if I had only known.  Live and learn I guess.

 

More than a year ago, when I was just experimenting, I bought a cheap Astromania laser collimator.

 

It has a variable power level for the laser unlike the HoTech.

 

Also surprisingly I can take it out and put it back in over and over and the laser hits the same spot.

 

I can also rotate it on the focuser and the laser does not move around.  Can't really do that test with the HoTech because of the rubber gaskets.

 

So until the Glatter arrives I will use that I guess.

 

Maybe CloudyNights needs a banner on every page that says... Only buy either a Farpoint or Glatter laser collimator.

[MellonLake]

Wait until you see how easy it is to align the secondary with the diffraction pattern produced by the small aperture on the Glatter.  

 

Rob  

[Vic Menard]

...primary collimation is pretty critical for high magnification performance.  For your telescope assuming it is F/4, you need to have the primary aligned within 0.7mm.

To be clear, the high magnification (30X to 50X per inch of aperture) primary mirror axial error tolerance for an f/4 primary mirror is 0.35mm. The error "read" in a Cheshire eyepiece (or equivalent) magnifies any residual primary mirror axial error 2X, so a 0.35mm error is a 0.7mm read.

 

...As I noted earlier with the non-Barlowed technique using the target on the Hotech the secondary alignment error adds to the primary alignment error.  So if your laser is off the centre of the mirror marker by more than 0.7mm you are not going to be able to achieve good primary mirror alignment

When using a simple thin beam laser, with a residual focuser axial error of 0.7mm (the outgoing beam alignment relative to the primary mirror center marker) the return beam alignment (collimated "perfectly" relative to the laser aperture/target in the focuser) will deliver a primary mirror axial error that's 1/2 of the residual outgoing beam error--in this case, 0.35mm.