Re: spotting scope question-specific


"Jerry Avins" <jya@xxxxxxxx> wrote in message
news:vZ6dneOZZqpbzIXZnZ2dnUVZ_v6dnZ2d@xxxxxxxxxx
The new low-dispersion glasses come close to good classic apochromatic
(apo) designs, but don't quite match them. If you find a used apo scope
in your price range, don't hold out for something more modern.

Not much of the cost of a good lens, let alone a scope, is in the glass.
The cost is in the shaping and polishing. Lenses with low-dispersion
glass command a higher price because of their better performance, not
because of higher per-unit manufacturing cost. We are still in the time
of retiring development costs and milking the market for the just
rewards or entrepreneurship, but I expect LD prices to fall eventually
to where they drive crown-flint achromats off the market. Have you
noticed that nowadays most lenses are multi-coated as a matter of
course? That was a high-end treatment not long ago.

Jerry,

Actually, one of the new low dispersion glasses, or fluorite, is the heart
of virtually any modern apochromat. ED glass is more expensive than the
vanilla crowns and flints, especially in the larger sizes used in high end
astronomical telescopes where the highest uniformity of indices is required.

Making and annealing optical glass is an energy intensive process. Folks
who know more that I about ED glasses claim prices are unlikely to go down
significantly, but I guess time will tell.

Clear skies, Alan

.

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