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Old 07-11-2018, 10:57 AM
Startrek (Martin)
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Startrek is offline
 
Join Date: Dec 2017
Location: Sydney and South Coast NSW
Posts: 5,990
Collimation ( advice for newbies like me )

I was one of those newbies who thought collimating my visual dob and astrophotography reflector was to just a simple case of using a laser collimator to adjust the secondary and primary and your done.However after more than a year getting away with just using a laser collimator I found out the hard way whilst imaging the lagoon nebula at my dark site taking 5 minute subs that something was wrong. Seeing conditions were perfect, no moon, no wind and no mozzies , but the images were showing stars with one end blurred and irregular shaped.I first though it’s my primary mirror as I moved it 4mm forward the previous week with cork spacers to give me more back focus on my DSLR.So I checked collimation with my laser collimator and it seemed ok.This had me stumped !! It wasn’t until I posted my problem on IIS that a few members advised to buy a Cheshire and adjust the secondary through the focuser sight tube. I found out it was out of alignment quite a bit even though the laser looked ok.Once adjusted and aligned I went out on the next clear night to perform some test images on bright and dim stars and they were perfect , tac sharp and nice sharp diffraction spikes. Problem solved !!
So the moral to the story is don’t just rely on your laser collimator , learn how to use a Cheshire and use your laser as a cross check that both secondary and primary are aligned.
Experienced IIS members were a huge help in sorting my collimation problem
Buy a Cheshire and learn how to use it ( it’s worth the $60 investment )
Cheers
Clear Skies
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