The laser collimator I have is 2" 635mm, with holographic and self-Barlow attachments. The holographic attachment is particularly useful for very precise collimation.
I have not yet tried the Barlow attachment. I think I will ask one of my more experienced club members to test it for me.
According to the link,
quote
"
Normally, a telescope takes parallel light rays from a distant star and converges them to a point at the eyepiece focus. Barlowed laser collimation takes advantage of the fact that a telescope will work in reverse. Placing a colllimator into a barlow lens will cause the parallel rays of laser light to diverge, apparently from a point just behind the Barlow lens. The diverging rays projected from the laser-Barlow combination in the focuser are turned into a beam of all-parallel rays when they are reflected from the primary, except for where the center mark on the primary prevents the mirror from reflecting. This reflected beam, containing a superimposed shadow of the collimation target, is projected up to the secondary, and then reflected to the focusser."
unquote
When I took my scope to Bintel Melbourne for some modification to the mount, I noticed Roger used this laser collimator to collimate my scope. That's why I went ahead to get one.
Cheers
