Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Collimation Question.

  • Please log in to reply
6 replies to this topic

#1 joe9520

joe9520

    Lift Off

  • -----
  • topic starter
  • Posts: 5
  • Joined: 19 May 2020

Posted 26 May 2020 - 09:19 PM

Hello,

 

After advice on this forum I have used a laser collimator to collimate my 8" dob. However I've noticed that when I get it dead center any moving of the screws on the eyepiece holder changes the position of the laser slightly so it isn't lined up straight anymore. Is this how it is or am I doing something wrong?

 

Thanks.



#2 Couder

Couder

    Mariner 2

  • *****
  • Posts: 224
  • Joined: 24 Feb 2014
  • Loc: Missouri Ozarks

Posted 26 May 2020 - 10:20 PM

In my experience the laser is probably slightly smaller the the eyepiece holder, so loosening the screw holding the laser in will change where the dot is. I suggest tightening the screw to where it barely, I mean barely keeps the laser in place, then rotating the laser. If the dot moves then your laser might be off.



#3 airbleeder

airbleeder

    Surveyor 1

  • *****
  • Posts: 1,924
  • Joined: 04 Jan 2014
  • Loc: Powder Springs, Georgia

Posted 27 May 2020 - 08:30 AM

   Secure the laser the same as you secure the eyepiece. 


  • Asbytec and rocketsteve like this

#4 MitchAlsup

MitchAlsup

    Skylab

  • -----
  • Posts: 4,366
  • Joined: 31 Aug 2009

Posted 27 May 2020 - 10:32 AM

A laser collimator is only collimated itself if it can be rotated in V-blocks while still pointing at the same spot on the wall. Any wobble and the collimator needs to be collimated.

 

Only a collimated collimator an be used to collimate a scope.

 

Secondarily, used properly a collimator can help one track down lack of stiffness in things like focuses, base plates, upper tube assemblies,... Once the laser is directly in the center of the ring on the primary, use mild pressure on the focuser, upper assembly,... to find the point(s) of flexure. Then fix it.



#5 MOwen

MOwen

    Vostok 1

  • *----
  • Posts: 140
  • Joined: 05 Mar 2018
  • Loc: Greenville, SC

Posted 27 May 2020 - 11:33 AM

You're not doing anything wrong.  In addition to what MitchAlsup said in the previous post about 'collimating' the laser itself, you probably also have a bit of play between the barrel of the laser and the eyepiece hole.  One trick you can try is to simply put a single layer of Scotch tape around the barrel to make it a more snug fit.  A full circle of tape might make the fit too tight so just experiment until you can still insert the laser easily but have removed most of the 'wiggle'.  At that point, the eyepiece screw should have much less (or no) effect but, with the snug fit, you're not going to need to use them.



#6 Asbytec

Asbytec

    Guy in a furry hat

  • *****
  • Posts: 17,087
  • Joined: 08 Aug 2007
  • Loc: Pampanga, PI

Posted 27 May 2020 - 03:08 PM

Or you could use a V block to rotate the laser to make sure it's well collimated by watching the laser spot on a wall. Many lasers allow you to adjust the beam so that it is pretty much true. Small deviations with the beam are OK,the smaller the better.

Once you're confident the laser is true, then I'd recommend collimating the focuser axis using the laser tightening the eyepeice adapter set screws the same way you use an eyepeice. This helps ensure if the laser is pointed at the primary center, then so will the eyepeice. Doing so minimizes registration (fit) error in the eyepeice adapter.

#7 SteveG

SteveG

    Cosmos

  • *****
  • Posts: 8,446
  • Joined: 27 Sep 2006
  • Loc: Seattle, WA

Posted 27 May 2020 - 04:23 PM

Hello,

 

After advice on this forum I have used a laser collimator to collimate my 8" dob. However I've noticed that when I get it dead center any moving of the screws on the eyepiece holder changes the position of the laser slightly so it isn't lined up straight anymore. Is this how it is or am I doing something wrong?

 

Thanks.

This is typical of cheap lasers. Your laser doesn’t fit snugly in the focuser. We call that the registration. As others have noted, the fix is to try to wrap it with something to make it slightly larger, and at the same time giving repeatable results. You may never get there with a cheap, 1.25 laser, such as the Lasermate.




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics