# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: camera sextant?
From: Marcel Tschudin
Date: 2010 Jul 6, 20:36 +0300

```George, you asked

"There are no error-bars shown on that plot, and it might be helpful
if they were, on account of its highly-expanded scale."

Hopefully Greg doesn't mind if I try to answer this question on his behalf.

For calibrating the 50mm and 100mm lenses the pixels seem to have been
measured once in each photo. I conclude this from the fact that all
pixel ranges which he posted to me had no decimals. (Please correct me
Greg if I'm wrong.) The possible error from the measured pixels is
therefore estimated to be +/-1 pixel. Looking at the mean values
obtained for the different lenses this corresponds to about:
50mm lens: +/- 0.4 moa
100mm lens: +/-0.2 moa
Since these calibrations are based on calculated sun heights one has
also to include the possible errors resulting from this calculation.
The height of eye was generally about 6ft. Assuming that this value
was estimated to +/-20% results in a dip error of 0.5moa; but since
the dip depends only by the square root from H.E. the error is only
half this value, i.e. +/-0.25 moa. Then we have the timing error: an
assumed value of +/-1sec is estimated to correspond at his latitude to
about +/- 0.3 moa. Putting now all of this together one obtains the
following expected typical errors
50mm lens: +/- 0.6 moa
100mm lens: +/- 0.4 moa
(I hope I got it about right.)

Greg, I hope you don't mind if I take this occasion to answer also
this question from George:

> We still haven't been told the overall size of the array that Greg is
> dealing with, which would tell us where its central point would be.
> Clearly, it must be similar to the array that Marcel refers to, which I
> take to be 3880 pixels, so that its centre is at 1940. Are they identical?

Yes. In the data Greg passed to me all were identical: 3880 pixels

Marcel

```
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