Barlowed laser collimation by Nils Olof Carlin?

[SkyHiker]

Hmm... In the Don Pensack's article it says:

1. Collimation cap (A simple peep-hole, though not good enough for scopes below f/10. I don’t recommend these except, perhaps, as a quick check to see if the optical elements are at least in gross alignment at the start).

2. Laser collimator (not useful unless perfectly collimated itself, possessed of a small beam diameter, and not accurate enough for primary mirror collimation unless used with a Barlow lens, but quite useful in the dark. Mfrs.: Glatter, FarPoint, etc.

The main take-away from DP's article are the geometry for the offset and non-offset case, and the general picture of what a collimated system looks like through the focuser. There are a gazillion confused users who expect the vanes to line up with the peep hole of a collimated scope, it does not. If you want to use measurements you have to program the geometry and measurements in the computer accounting for all offsets, etcetera. This is not easy and is best avoided since it is also not necessary.

I never read the Catseye stuff, see Nils Olof's FAQ for a reality check on what he thinks about Catseye.

About the preference of laser vs collimation cap vs Barlowed laser, this seems to vary from author to author so I would not take that too seriously unless it is backed up with thorough evidence. Also keep in mind that it's an article that promotes a different method.

I collimated my Mak-Newt last night with the Howie Glatter and tublug. The tublug has a lens that acts like a Barlow. The shadow of the donut shows up nicely, it works really well. At first I thought I overpaid for it but now I'm glad I have it. A big part of it is also a quality fit so the laser is not flopping around in the focuser. It's a joy to use.

I also have a Z12 laser collimator that I used until the battery ran out. It worked OK until then but the laser dot really started drooping when the battery ran out. Then I have a dirt cheap Seben LK1, it needed collimation and tape to get it set firmly in the focuser. But it can be made to work fine. I also have a brand-less and hair-less Cheshire that is useful if the laser misses the secondary.

[turboscrew]

I think Chesire is quite commonly mentioned as a good way. And collimation caps seem to have their own uses.
Also tublug is rumored to be quite good.

BTW, I figured out the offset. Draw some simple picture and started calculating - basic trigonometry, really. I got the same result: offset = secondary mirror minor axle / 4F. Took some time to figure out where to start, though.
It became clear in the beginning that the horisontal offset must be equal to the vertical offset - it's just sliding the mirror backwards in 45 degree angle.