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> Bill you wrote:
> "My question, can I use any sharp line to test/adjust even if it is  only
> several hundred yards away?  My guess is yes, as parallax between  the
> horizon and index mirrors should not be a problem, but my guesses are  so
> often in error."

Frank replied:
>
> Since your post is titled "side error", I assume that you're lining up the
> direct and reflected image of a vertical line, and yes, in that case parallax
> in  the instrument is no problem.

Correct

> BUT in my opinion, side error is no problem
> and a  little mismatch (maybe one minute of arc) in the direct and reflected
> images may  actually be useful in some circumstances.

Thanks Frank

If I recall the a list member stated a wee bit of side error can help with
star-to-star distances (as well as determining IE/IC with stars I assume).
With a 3.5X scope--even with a faint star and tripod-mounted sextant--it
pushes my limits to align those dots precisely.

In one Sun IE check I was focusing my scope (which seems to drift due to eye
fatigue after 20 or 30 shots) and noticed a tiny sunspot.  I used that spot
(and the side error helped a bit) to superimpose the reflected and glass
image.  The value agreed within 0d 00!03 to the average of a series of ten
tripod-mounted-sextant upper- and lower-limb tangencies.

I have never seen using a sunspot in texts. Is it fair game when available,
or did I just get lucky with my correlation?

Bill

   

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