Jump to content


Photo

Barlowed laser collimation

  • Please log in to reply
4 replies to this topic

#1 sideshowkevin

sideshowkevin

    Explorer 1

  • -----
  • Posts: 54
  • Joined: 07 Sep 2012
  • Loc: Pittsburgh, PA

Posted 12 October 2012 - 03:35 PM

I have been using the barlowed laser technique to collimate my 10" Apertura Dob. I use the laser collimator they supplied in the accessory package bundled with the scope.

Today I took off the secondary to install milk jug washers. Oh my! How buttery smooth the secondary adjustment is! But I was having problems seeing the laser and so I headed off to the store to pick up some new batteries.

With those installed, I couldn't believe how bright the laser was. Guess I should have done that a while ago! But as I was collimating, I notice something new only because the laser was so bright. I noticed a slight leak of light off the edge of the secondary - like the annular ring around a solar eclipse - projected on my wall. When I fiddle with the barlowed laser in the focuser by adding a little leverage, I can move the ring around slightly, but it never disappears.

But then I noticed that when I loosen the set screw and rotate the laser in the barlow, I see a wide change in how light escapes from the secondary and hits my wall. In fact, it is worst when the laser collimator is rotated 180° from the normal position I use to see the ring while adjusting the primary, and most of the de-focused laser light is off the secondary mirror.

So now I am a little confused if I need to work on my secondary alignment, or if I need to work on the collimation of the laser? I haven't noticed collimation issues so far when I de-focus stars, so I am not sure what I need to check. Tonight is clear here, so I guess I will see if I notice any visual differences from last night.

#2 Jason D

Jason D

    Fly Me to the Moon

  • *****
  • Posts: 6667
  • Joined: 21 Oct 2006
  • Loc: California

Posted 12 October 2012 - 04:22 PM

Today I took off the secondary to install milk jug washers. Oh my! How buttery smooth the secondary adjustment is!

:waytogo:


like the annular ring around a solar eclipse - projected on my wall.


Ignore it. It does not mean much. Your laser field stop (laser opening) seems to be scattering some laser which explains the phenomenon your have described but the scattering is unlikely to be even which explains the 180 degree anomaly you have described.

Jason

#3 evil16v

evil16v

    Explorer 1

  • -----
  • Posts: 85
  • Joined: 18 Aug 2012
  • Loc: N.E. Kansas

Posted 12 October 2012 - 08:56 PM

I have an AD8 and the same laser collimator. Take the Barlow out and just put it in the 1.25" adapter, and in the focuser. With it aligned inside your circle sticker on your primary, see if rotating the laser and re tightening the focuser adapter changes where the dot is on your sticker. try at every 90* of rotation. Then go back to original position and see if it repeats. I had a little trouble getting mine to repeat early on. I think something with the set screw and the brass ring seated. The problem went away.


Oh... and how do you like your ES 82's? I am wanting the Focal lengths in your sig. Your scope is a little faster than mine but may be comparable....

#4 sideshowkevin

sideshowkevin

    Explorer 1

  • -----
  • Posts: 54
  • Joined: 07 Sep 2012
  • Loc: Pittsburgh, PA

Posted 13 October 2012 - 08:51 AM

Well, I seemed to have a good de-focused star last night, so I will take Jason's advice and not worry about it!

Rob, about the ES 82° - I love them. They are optically clear and really easy to snap to a focus. I will hopefully be able to take advantage of the sale through the end of the year and pick up some of the 2" ones, but as a start for you I would recommend the 14mm, because it will fall nicely in between the range you already have. And at 33% off, you can't beat the sale price.

#5 evil16v

evil16v

    Explorer 1

  • -----
  • Posts: 85
  • Joined: 18 Aug 2012
  • Loc: N.E. Kansas

Posted 13 October 2012 - 09:18 AM

Well, I seemed to have a good de-focused star last night, so I will take Jason's advice and not worry about it!

Rob, about the ES 82° - I love them. They are optically clear and really easy to snap to a focus. I will hopefully be able to take advantage of the sale through the end of the year and pick up some of the 2" ones, but as a start for you I would recommend the 14mm, because it will fall nicely in between the range you already have. And at 33% off, you can't beat the sale price.


I just figured I'd mention it since you had the same focuser.

The 14 and the 6.7 are high on my list. optics mart only has 8.8's, which are low on my list. I'd like to try them... if they ever become available.... :tonofbricks:






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics