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>
>
> It's possible to go overboard on magnification, either in binoculars
> or a sextant scope or monocular.  Past a certain point, the platform
> you're shooting from becomes a signifcant issue.  As the boat pitches,
> rolls, and yaws, that motion is also magnified.  7X seems to be a
> reasonable compromise on this issue for binoculars, for example.  With
> a sextant, where the field of view is limited to begin with and
> putting two images into a specific relationship is crucial, lower
> powers are needed.

ABSOLUTELY!  I always tell people at football games--don't go for power, go for objective
size and apparent field of view--you'll enjoy them more.  6x is FAR more useful than 10x from
the stands.

> The question is one of accuracy; not ultimate, "good enough only for
> NASA" accuracy but reasonable, "I'm pretty sure we're here" accuracy.
> If a round of sights is erratic, the confidence in the final result is
> reduced.  With magnification (subject to the constraints above), it's
> possible to get the limb of the Sun or Moon smack on the horizon with
> greater confidence *and do so repeatedly*.  This produces (with
> practice) consistant accurate results which, in turn, leads to
> justifiable confidence in the sights.
>
> Talking about optics, I want to clarify a point about magnification.
> 6X30 monoculars (the "30" is the diameter of the front lens in
> millimeters - i.e., 30mm) are intended for Sun (and Moon) sights while
> the lower power 2.5X or 3X scopes are much better for star and planet
> shots.  As the magnifcation of a system goes up, assuming the lens
> diameters remain constant, the scope's light gathering ability
> decreases.  Clearly, neither the Sun or Moon are dim objects so the
> loss of light gathering in a 6X30 monocular is not an issue.  With the
> dimmer nav stars or planets (Mars or Saturn), reducing the
> magnification helps.  Since all of these targets are effectively point
> light sources, there's little information lost (save, possibly some
> resolution of the horizon) with the reduction of magnification.

I mostly agree, but as all astronomy buffs know, light gathering ability is far more
important than magnification. You can see far more with a 10" scope at 75x than a 3.5" scope
at 150x, especially when dealing with point light sources.

>
>
>  > As for the lathe analogy: here I believe Rick has missed my point. The items he omits
>  > are necessary to the operation of a lathe (specifically, a metal lathe, not a wood
>  > one, as my dad was a machinist) and to overcome them would require even a skilled
>  > machinist to go to extraordinary lengths are are akin to omitting the sight tube, sun
>  > filters and vernier marks on the index arm.  Yes, it's that extreme.  It's nice to
>  > have auto-feed, auto-cleaning, and computer control on a lathe--it certainly speeds
>  > both setup and production and are pay for themselves, but they are not needed.

> None of
> them connect to computers (whatever became of those projects?), have
> gyro stabilizers (why doesn't Canon work on that?), or other "chrome".

GPS killed those projects.  You can buy a GPS w/ PC connection for the cost of a Mark 25.  If
electricity is not a concern, why bother with sextant to PC? (of course I don't want to get
into the GPS/ sight reduction debate--we all know the issues). I LIKE the idea of a Canon
stabilizer! How 'bout it guys?

> Where they differ most is in the precision of their construction and
> the materials they're made from.  Lathes, it seems to me, are far more
> varied and complex.

Naw, not old ones. My dad has one in his cellar that must be70 years old and still working.

>
>
>  > Rick has clearly been better at finding good, used and new sextants at bargain prices
>  > than I have and I will defer to him on that.
>
> Gee, I wish my wife was as kind on that point!  [grin]

If she figures every buck spent on a sextant is wasted, you are SOL. [double grin]

>
>
> I don't argue that a potential student should rush out and spend top
> dollar on a sextant any more than, in my ski instructor days, I'd
> argue for buying top of the line skis to learn to snowplow (sorry,
> PSIA, make that "perform a gliding wedge").  I do argue, however, that
> below some level, the student's equipment makes the learning process
> avoidably more difficult.

Now you know why I don't ski...

>
>
> I saw this happen with a friend who was trying to make a Freiberger
> Yachtsman work.  He was having little success in getting a good round
> of sights so I asked to have a look.  The filters were hazy and the
> mirrors were more mirrors in name than in deed.  Exchanging the
> Freiberger for an Astra, he made a great deal of progress in minutes.
> The condition of this particular sextant is, I hope, atypical but it
> does point out that less than adequate gear is a significant hindrance
> to learning.

I was shocked, on the WindSurf, to learn they are stocked with Friebergers, not Plaths or
Tamiyas.

It's been fun guys, but I must get to work.

ATB,
Carl.

   

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