NavList:

Sean.

Use the 4x40 scope to determine index error then switch to the sight tube for observations. Try side by side images of the Sun in the artificial horizon rather than limb to limb. Shade the Sun until it is just visible for both direct and reflected images. Match the brightness if possible. I get no worse than +/- 1.5' intercepts using the sight tube with an artificial horizon vs. +/- 1.0' with the 4x40 scope. Keep after it. Hold off on the 7x35 scope unless you plan on doing lunars or making observations from a ships bridge or at the beach from well above sea level. I find the 7x35 scope very difficult to use with an artificial horizon.

Greg Rudzinski

From: Sean C
Date: 2015 Oct 8, 21:00 -0700

I recently received a zero magnification sight tube for my Astra IIIb. I tried it for the first time today. I was taking sun sights with my Davis artificial horizon. I must say, I found the sight tube much more difficult to use than the standard 3.5X scope. I got widely varying results when trying to determine index error. (I used the limb-to-limb mehtod.) Errors for the actual sights ranged from +3.4' to +5.3' and my average error for a round of nine sights was +4.7'. I'm going to try some more sights and hope my accuracy improves as I get used to it.

I'd be interested to hear others' experience with it and how you compare/contrast it with a 3.5X or even 7X scope (which I am considering purchasing, as well). Thanks!

Sincerely,

Sean C.