[time-nuts] A real world project need for timing accuracy...

William H. Fite omniryx at gmail.com
Tue Nov 2 15:45:51 UTC 2010


Bob said:
If you were going to do precision optical work at these distances, you would
do it over a cool surface at night rather than a hot surface.

And in the winter during nights with very low humidity and not a trace of
wind.

Or you would pay the truly humongous bucks for an optical perturbation
analyzer/canceller, aka an adaptive tip-tilt corrector (cf. Keck telescopes)

And two semis to haul it and a team to set it up and calibrate it....




On Tue, Nov 2, 2010 at 11:26 AM, Bob Camp <lists at rtty.us> wrote:

> Hi
>
> The issue is that you are trying to view over a heated surface (close to
> the
> ground in sunlight). The distortion induced by the "thermals" is enormous.
> The the target "as viewed" does indeed move around. In the absence of
> atmosphere and it's issues, the problem would be much easier in a number of
> ways.
>
> If you were going to do precision optical work at these distances, you
> would
> do it over a cool surface at night rather than a hot surface.
>
> Bob
>
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of jimlux
> Sent: Tuesday, November 02, 2010 9:28 AM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] A real world project need for timing accuracy...
>
>  Bob Camp wrote:
> > Hi
> >
> > Ok, I mis-understood the question.
> >
> > In my experience, you can have big buck (as in many thousands of dollars)
> optics and not see .2" holes at 800 yards. The bull's eye is a *lot* bigger
> than the hole the bullet made.
> >
> >
> 0.2" at 2400 ft is about 0.08 milliradian.. or 0.3 minutes of arc.  Your
> eye can resolve about 1 minute of arc... I'm not questioning your
> experience, but it seem that even a moderate power scope should allow
> you to see the holes.  As I recall, the Rayleigh limit for resolution is
> something like 0.7 milliradian/mm of aperture, so 10-15 mm aperture
> would be in the right ballpark..
>
> I can imagine needing more aperture than 3", though.. you're not
> interested in resolving a star, but something more akin to separating dots.
>
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