barlowed laser

[gary1968]

Howdy,

I am never convinced that my 8" newt is collimated correctly as I could never understand all the reflections and circles you get with a cheshire so I bought a Baader Laser Collimator.

I have been using this since last christmas and have been fairly happy with the results. I read recently about using a barlow with the laser as it is supposed to be more accurate so I tied that last night.

I collimated the scope with only the laser to start with and got it pretty good. I then fitted my Antares 2x barlow and tried again, the 'footprint' of the laser was now about 1" away from the centre of the primary, indicating to me that the secondary was out. I adjusted the secondary to bring it back in line and it looked fime. I then rechecked with only the laser and found it to be out by the same amount the other way. I have readjusted it using only the laser again and checked it with a home made collimation cap and it seems to be ok, still to star test though.

Any of you guys came across this problem before? Or can suggest whether the laser on its own would be more accurate than with a barlow........

Cheers,

Gary

[tony4563]

Hi Gary.

Good post. I always wondered why a Barlowed Laser is supposed to be more accurate? :scratch:

I too use a Baader Lasar Collimator and find it bang on. After the scope has cooled, I usually centre the focusser in the secondary with a Cheshire eyepiece then align the mirrors with the Laser as per instructions.

Doing a star test, I get perfect concentric circles and that will do for me :mrgreen:

[rawhead]

Have a read of this

http://astro.neutral.org/eq/col.html

[gary1968]

Thanks fro that rawhead, a good read. All that makes ense to me, but, I dont think it explains why thelaser position on the primary is different with and without the barlow, or am I missing something?

Gary