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Fred wrote

> Bill,
>
> Some dumb suggestions, in no particular order of priority.

Boy Howdy, Fred, don't sugar coat it, tell it like it is.  At least how you
would like it to be so you can jump all over it like a monkey on a
trampoline. 
>
> First, you mentioned you add a slight side error to improve star IC
> checks.  Have you tried nulling that out?

Wrong. Perhaps you were remembering a post in which Frank stated a little
side error could be a good thing--eons ago. Side error is nulled out.  50d
from vertical, natural horizon, no apparent side error.  Notta, zip, zilch.
I wrote, "NOTE:  All sun IE checks were made without changing focus, as this
will change IE and side error with my scope."  I apologize if my statement
led you to believe I had ignored or  introduced side error for some positive
purpose.  To clear that up let me restate.  All sun IE checks were made
without changing focus, as this will change IE and INTRODUCE side error with
my scope.
>
> Second, have you had others try an IC check on the sun with your
> sextant and compared to yours?

Yes, and stars.  Perhaps 0.2' or more difference.  This is also when I
nailed down my hypothesis that side error and IE shift with focus.  I had
side error as close to zero as humanly possible.  Alex refocused and did
some IE checks with my unit (stars), and told me there was side error.  I
refocused to my eye and told him there was not.  Subsequent trials and
tripod mounted tests proved that BOTH IE and side error shifted with focus
change.
>
> Third, have you tried changing the position of tangency to try to at
> least get the SDs to agree?

"Tangent" is by definition "tangent."  It is not, nearly touching.  It is
not overlapping.  It is tangent.  Can I fudge my observations to make them
agree with 4 SD? Sure.  What is the point?  Better to nail it mathematically
and adjust than try to judge "nearly tangent" by eye IMHO.

While on the subject of matching published 4SD exactly, I find that foolish.
SD 15.8" one day, 15.9' the next.  4SD jumps from 63.2' to 63.6' in one day?
Really?  No, not really.  It's at a rounding point, so SD is closer to
15.85'.  And 4SD closer to 63.4'.  In my case, it was pretty near the 15.8'
midpoint, so that was what I used.  Even with +/- 0.1 precision and accuracy
(instrument and observer combined) and two observations (one on the arc and
one off the arc) 0.2' off 4SD is asking a lot in my opinion.
>
> Fourth, the 4x telescope for my C+P shows changes in side error
> depending upon the focus setting.  Is anything like that happening
> with yours? (I don't know this would affect the sights.

At last we are on the same page.  As I stated, "NOTE:  All sun IE checks
were made without changing focus, as this will change IE and side error with
my scope."  I did not state I used the same focus for horizon checks and sun
checks.  My sin of omission.

Yes indeed. Changing focus on my scope will change (introduce) side error,
and any other scopes I have tested.  It also will change IE. I think of it
like Polaris's rotation about the pole. In most cases both the X and Y axis
are affected by a change in focus.  An indication the lenses of the scope
are either not perfectly ground or there are lens collimation issues with
the scope. (Internal errors, as opposed to frame/scope collimation errors.)

I have long respected your abilities and opinions, so if the above and
earlier posts are "dumb" to you, so be it.  I trust you will, in kind,
respect my right to disagree.

Bill


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