20 replies to this topic

[Senex Bibax]

Out of curiosity, I just removed the diagonal from my Meade 310 and inserted my laser collimator into the visual back. When I aimed the scope at a wall and turned on the laser, the resulting spot of light projected onto the wall was somewhat elongated, roughly bean-shaped, and rotating the collimator made no difference.

 

Would you expect to see a round spot of projected laser light if the objective was properly aligned in the OTA, and the elements were correctly aligned and spaced? I would have thought so...

[Couder]

Two ways to look at this.

1) If you like the views, then enjoy it.

2) You can worry and fret about it, have the optics tested, then what?

[ccwemyss]

If the focuser isn't collimated, the beam from the laser could be going through at an angle. Are you sure it is hitting the objective dead center?

 

Chip W. 

[DAVIDG]

  The procedure I have used for years to correctly collimate a refractor with a laser is 

  1) First make sure your laser collimator is correctly aligned by putting  it in V block and  looking at the spot on a wall at least 6 feet away to make sure it does move when you rotate the collimator in the V block . Almost all the collimators I have tested are out and need to be correctly aligned. I have seen the laser make a circle 6" in diameter ! 

  2) Make a paper mask the size of the objective with the center marked

  3) Place the mask over the objective so it is perfectly centered.

  4)  With the laser in the focuser, the beam needs to hit the exact center of the mask. If not adjust the focuser so it does. Now the  mechanical axis of the focuser and the lens are aligned

  5) Remove the mask and point the scope at a wall about 6' or farther away. You will see one bright stop and if the lens is not aligned a couple of fainter spots around the bright one. Adjust the tip and tilt of the lens so all the spots merger into the bright one. Your refractor is now perfectly collimated.

 

              - Dave 

Edited by DAVIDG, 22 March 2025 - 08:50 AM.

[sunrag]

I would add one more check. This is a check of the spacing between the Achromat elements. Use a monochromatic light (e.g. a green laser beam diffused by packing foam) and shine it on the objective lens. If the spacing is uniform, you will see a well centered concentric set of rings (Newton’s Rings). If the rings are not centered on the objective’s center, this indicates that the spacing between the elements is not uniform. This is most likely caused by the spacers being either improperly positioned or different thicknesses.

 

 

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Edited by sunrag, 21 March 2025 - 10:59 AM.

[Senex Bibax]

Two ways to look at this.

1) If you like the views, then enjoy it.

2) You can worry and fret about it, have the optics tested, then what?

How about a third way to look at it? I wouldn't bother if I was satisfied with the views. I'm not worrying or fretting, I'm looking for a simple way to check if the objective is suffering from astigmatism or misaligned. I have had the objective out of its cell, replaced one missing foil spacer, and confirmed that I can see Newton's rings under a fluorescent light.

 

I'll repeat the laser test using a paper mask to verify focuser alignment, as per DAVIDG's suggestion.

[DreamWeaver]

Are you sure your laser collimator is producing a round dot?  The two lasers I have produce an oblong dot.

 

https://www.cloudyni...-strange-shape/

[deSitter]

  The procedure I have used for years to correctly collimate a refractor with a laser is 

  1) First make sure your laser collimator is correctly aligned by putting  it in V block and  looking at the spot on a wall at least 6 feet away to make sure it does move when you rotate the collimator in the V block . Almost all the collimators I have tested are out and need to be correctly aligned. I have seen the laser make a circle 6" in diameter ! 

  2) Make a paper mask the size of the objective with the center marked

  3) Place the mask over the objective so it is perfectly centered.

  4)  With the laser in the focuser, the beam needs to hit the exact center of the mask. If not adjust the focuser so it does. Now the  mechanical axis of the focuser and the lens are aligned

  5) Remove the mask and point the scope at a wall about 6' or farther away. You will see one bright stop and if the lens is not aligned a couple of fainter spots around the bright one. Adjust the tip and tilt of the lens so all the spots merger into the bright one. Your refractor is now perfectly collimated.

 

              - Dave 

Yes I bought mine expecting it to be noticeably out of whack. To my amazement, it was perfectly calibrated. There are three adjusters covered over with some black plastic in case adjustment is needed.

 

-drl

[deSitter]

Are you sure your laser collimator is producing a round dot?  The two lasers I have produce an oblong dot.

 

https://www.cloudyni...-strange-shape/

Yes he checked for that.

 

-drl

[DreamWeaver]

Yes he checked for that.

 

-drl

That comment must have been deleted then. 

[Senex Bibax]

Looks like everything is ok. I checked my collimator again yesterday and the dot is definitely oval, not round.

[deSitter]

Looks like everything is ok. I checked my collimator again yesterday and the dot is definitely oval, not round.

You said "...the resulting spot of light projected onto the wall was somewhat elongated, roughly bean-shaped, and rotating the collimator made no difference." - I took this mean what it said, that your rotated the collimator and the bean shape did not rotate with it. That would not be down to the shape of the beam.

 

-drl

[deSitter]

Are you sure your laser collimator is producing a round dot?  The two lasers I have produce an oblong dot.

 

https://www.cloudyni...-strange-shape/

I seem to remember mine is a small square for a source. The oblong-ity is probably beam spread.

 

-drl

[DreamWeaver]

You said "...the resulting spot of light projected onto the wall was somewhat elongated, roughly bean-shaped, and rotating the collimator made no difference." - I took this mean what it said, that your rotated the collimator and the bean shape did not rotate with it. That would not be down to the shape of the beam.

 

-drl

I was guessing differently than you.  I took it to mean that the oval shape was rotating. You should hear some of the conversations my British wife and I have, misunderstanding what the other one is trying to describe.  Even though we speak the same language…sorta.  

[Kasmos]

I was guessing differently than you.  I took it to mean that the oval shape was rotating. You should hear some of the conversations my British wife and I have, misunderstanding what the other one is trying to describe.  Even though we speak the same language…sorta.  

Sometimes it's the same with my wife and me and neither of us is British. Maybe it's more of a Male Female thing? 

[Senex Bibax]

Hmm.. I didn't think about the fact that the projected spot didn't change when I rotated the collimator in the visual back. Maybe time for more investigation..

 

I can share the laughs about language mixups. I was born in England but haven't lived there since I was six years old. Lived most of my life in Canada, but still understand the nuances of British English vs Canadian vs American. Then to complicate things, my own family relocated to Australia for two years back in 2008, with a whole new bunch of complications to watch for ("rooting around" is a great example).

 

On top of all that, my wife is Swedish, and learned British English in school, now altered after 30 years' living in Canada. We lived in Sweden for five years after we met, and while I am fluent in the language, we still get our wires crossed occasionally regardless of which language we use - frequently a mix.

[deSitter]

Hmm.. I didn't think about the fact that the projected spot didn't change when I rotated the collimator in the visual back. Maybe time for more investigation..

 

I can share the laughs about language mixups. I was born in England but haven't lived there since I was six years old. Lived most of my life in Canada, but still understand the nuances of British English vs Canadian vs American. Then to complicate things, my own family relocated to Australia for two years back in 2008, with a whole new bunch of complications to watch for ("rooting around" is a great example).

 

On top of all that, my wife is Swedish, and learned British English in school, now altered after 30 years' living in Canada. We lived in Sweden for five years after we met, and while I am fluent in the language, we still get our wires crossed occasionally regardless of which language we use - frequently a mix.

George Bernard Shaw famously quipped that the British and Americans were "two peoples separated by a common language"

 

-drl

[deSitter]

Hmm.. I didn't think about the fact that the projected spot didn't change when I rotated the collimator in the visual back. Maybe time for more investigation..

 

 

 

I seem to remember that my collimator has a squarish beam - don't know if it's a window or the actual active element like an LED flashlight. I think they are diode lasers and make an elliptical beam, which is then collimated with funny lenses to circularize it. I can distinctly see lack of roundness at low power.

 

-drl

[Jon Isaacs]

For what it's worth:

 

25 years ago I purchased a 1.25 inch Howie Glatter collimator.  18 years ago, I purchased a 2 inch Howie. Howie's alignment spec was 1 mm at 44 feet. (15 arc-seconds)  I check them every so often. I believe they're still in spec. 

 

They both have 1 mm aperture stops and produce nice round spots.

 

 

These days they're quite expensive, quite an investment for occasionally aligning a refractor focuser. It's worthwhile if one frequently collimates Dob's.

 

 

Not your typical laser collimator.

 

 

Jon

[deSitter]

 

For what it's worth:

 

25 years ago I purchased a 1.25 inch Howie Glatter collimator.  18 years ago, I purchased a 2 inch Howie. Howie's alignment spec was 1 mm at 44 feet. (15 arc-seconds)  I check them every so often. I believe they're still in spec. 

 

They both have 1 mm aperture stops and produce nice round spots.

 

 

 

These days they're quite expensive, quite an investment for occasionally aligning a refractor focuser. It's worthwhile if one frequently collimates Dob's.

 

 

 

Not your typical laser collimator.

 

 

 

Jon

 

That's probably a gas laser. (He-Ne)

 

-drl

[Jon Isaacs]

That's probably a gas laser. (He-Ne)

 

-drl

 

It's just a 635 nm Laser diode. 

 

Jon