NavList:

Greg,

Try using a stopwatch for timing of a rising or setting body then compare to observations made when the body is at or near meridian passage where timing isn't as critical. Tape the scope ocular so that the focus can't accidentally change. Be sure to use the center of the scope field. Most scopes do not have cross hairs to assist in centering.

See how good you can do in determining index error. You will need to get this down to +/- 0.25' first before moving on (not that easy).

I would try the 7x scope before buying. You may not like the limited field of view.

Greg Rudzinski

Re: Is a 7X scope worthwhile?
From: Greg Licfi
Date: 2014 Feb 14, 21:48 -0500
Lu,
If you are correct the 'systemic error' may be a perceptual bias
that I can compensate for with a little more practice.
I have done several checks that seem to indicate that the sextant
is in fine working order. Your observation about your
boat would be even more pronounced on my little C28 and I quite
agree with that. Yet I would like to get my land sights
up to the +/- 0.25' error that has been mentioned here.
~Greg

On 02/14/2014 09:16 PM, Lu Abel wrote:
Greg:

First of all, it sounds as if you have some sort of systemic error if your sights are always coming out with the same 0.5 or 1.0 inconsistency.

Second, the usefulness of a 7x scope will clearly depend on the stability of the platform you're on (as well as the stability of your hand). I've taken shots from my 36' sailboat and in anything but a dead calm it rocks enough that it's hard to get a good shot even with a 1x scope. You're trying with an AH, presumably on land. Might work there, doubt a 7x scope would work at sea unless you're on a very large ship.

On 2/14/2014 3:56 PM, Greg Licfi wrote:
Hi all,
My question du jour is: Is a 7X scope worthwhile?
I have been taking as many AH practice sights as I can lately, (when the weather cooperates)
I have also been doing slope fits for my multiple sights and find my data consistent.
My problem seems to be that I am always 0.5 to 1.0 Towards, I am using the 'set & wait
technique' and letting the sun come down to the AH image. I do a slow rocking of the
sextant and mark my time at what appears to be the instant of touching. I think I read once
(in a NavList post?) that a 7X scope could improve sun & moon sights by virtue of the fact
that the image would be bigger. Obviously (I think) my images are not actually touching - even
though I believe they are. My eyes might benefit from the increased size. What say the jury?
Last question: Has anyone here ever cannibalized a 7X binocular to make a 7X scope?
I think it is possible and some of the prices I've seen for 7X scopes would make them
prohibitive on my budget.
Thanks!
~Greg

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