NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: "Improved" sextants
From: Bill B
Date: 2006 Jul 4, 00:32 -0500
Greg R wrote:
> And (assuming we were still going to use human sight-takers), I'd add a
> request for a zoom lens on the telescope. Never figured out why nobody
> has done that yet (that I'm aware of) - use the wide-angle setting to
> get the object into the field of view, then zoom in as necessary for
> that perfect horizon kiss.'
I had inquired about that a year or so ago, no takers. My guess, based on
photo optics, is the problems are many.
1. Zoom optics are generally inferior to prime (fixed focal length) optics,
and in general sextant optics suck when compared to a camera lens with lens
mounts, aperture selection etc. or binoculars at the same price point.
Small volume/high price.
2. Zoom lenses are heavier.
3. Zoom lenses in general are slower (transmit less light) than their
prime-lens counterparts. No problem for the sun, problem for stars.
4. Zoom lenses are more mechanically (and optically) complex therefore less
robust (and probably a pain to seal off the elements).
Along the same line, why not add a diaphragm to fine tune light levels?
Seems like rotating polarizing filters is the best we have to date. Simple
and robust.
In the end, and for all the critics, the sextant, almanac (which was not
always done by computers),tabular methods will get us where we are going,
with a timepiece or lunars, quite well.
One might make the argument that with *only* a sextant and compass, one is
like a survivalist armed with a cache of weapons but no ammunition. I would
suggest a the pole star, a simple circle divided into 365 parts to determine
the sun's rough declination, or giving our own name to stars (as Ken
presented in one of his seminars) can get you to the point where coastal
piloting kicks in. Folks have been getting from pint A to point B with a
lot fewer high-tech (now low-tech) instruments and knowledge for most of
recorded history.
But I digress--end of rant.
Bill
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To , send email to NavList-@fer3.com
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From: Bill B
Date: 2006 Jul 4, 00:32 -0500
Greg R wrote:
> And (assuming we were still going to use human sight-takers), I'd add a
> request for a zoom lens on the telescope. Never figured out why nobody
> has done that yet (that I'm aware of) - use the wide-angle setting to
> get the object into the field of view, then zoom in as necessary for
> that perfect horizon kiss.'
I had inquired about that a year or so ago, no takers. My guess, based on
photo optics, is the problems are many.
1. Zoom optics are generally inferior to prime (fixed focal length) optics,
and in general sextant optics suck when compared to a camera lens with lens
mounts, aperture selection etc. or binoculars at the same price point.
Small volume/high price.
2. Zoom lenses are heavier.
3. Zoom lenses in general are slower (transmit less light) than their
prime-lens counterparts. No problem for the sun, problem for stars.
4. Zoom lenses are more mechanically (and optically) complex therefore less
robust (and probably a pain to seal off the elements).
Along the same line, why not add a diaphragm to fine tune light levels?
Seems like rotating polarizing filters is the best we have to date. Simple
and robust.
In the end, and for all the critics, the sextant, almanac (which was not
always done by computers),tabular methods will get us where we are going,
with a timepiece or lunars, quite well.
One might make the argument that with *only* a sextant and compass, one is
like a survivalist armed with a cache of weapons but no ammunition. I would
suggest a the pole star, a simple circle divided into 365 parts to determine
the sun's rough declination, or giving our own name to stars (as Ken
presented in one of his seminars) can get you to the point where coastal
piloting kicks in. Folks have been getting from pint A to point B with a
lot fewer high-tech (now low-tech) instruments and knowledge for most of
recorded history.
But I digress--end of rant.
Bill
--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to NavList@fer3.com
To , send email to NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---
