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Fred,

Some say the C. Plath scopes were made by Carl Zeiss, and one respected
European specialist in sextants feels the Plath 6 x 30 is the best scope
made for a sextant. I have used the Tamaya 7 x 35 for conditions described
below, and except for LAN sights and relatively calm conditions, never liked
its weight or narrower field of view.

Some other considerations to consider are:

A 4 x 40 is considered a STAR Scope because it transmits more light through
the optics than higher powered scopes. Its wider field of vision is an
advantage in low light conditions.

The 6 x 30, 7 x 35 and 7 x 50 are considered SUN scopes because the higher
power adds greater definition to the horizon and the sun's limbs. It really
makes for a precise LAN sight. On bright nights, they work well with the
moon. and are good for shooting early rising planets at twi-light.

Many sextants prior to the mid 1970's were fitted with higher power scopes,
6 x, 7 x. The 4 x 40 became popular as a standard thereafter, and the higher
powered scopes became fitted as an option.

As you know, when power increases, the ability to keep a steady image
decreases. Anything over 7 x 50, unless stabilized, has too narrow a field
of vision, and the image moves too much to be of much use from small craft.

When given in the specs,  Relative Brightness, Relative Light Efficiency
(adds 50% for coated lens to RB), and Twilight factor are helpful in
comparing the amount of light that reaches the eye between various scopes.

For terrestrial objects, all you need is a sighting tube, magnification is
unnecessary because you need to be fairly close in to shore to make out the
objects and identify them. Those who collect antique sextants know that many
just had sighting holes in a vane which was typical of early instruments.

Joel Jacobs

----- Original Message -----
From: "Fred Hebard" 
To: 
Sent: Saturday, March 27, 2004 11:55 PM
Subject: Sextant Telescopes


> What are the relative merits of the Tamaya 7x35 telescopes and the
> Plath 6x30s?
>
> Thanks,
>
> Fred

   

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