Whenever one buys equipment that's at the cutting edge of technology,
whenever that equipment is completely new with only one or two manufacturers
competing, the price will naturally be very high. There is no question in
my mind that the price will come down some way down the road when more
manufacturers jump in.

Yes, the equipment is at the cutting edge of technology. No, I don't think they
will ever come down in price when more manufaturers jump in. The level of
accuracy required to make etalon plates makes them very expensive.

The only other way to get ultra-narrow bands is to apply many layers of
evaporants (100 layers) on a piece of glass. The layers have to be very exact
in thickness and have the proper refractive index.

Baader Planetarium has tried for years to get this scheme to work in the
sub-angstrom range without success, even with the most sophisticated Leybold
electron beam coating equipment. The best they have managed to do is about 1.5
Angstrom on selected pieces. This is not good enough to show Ha surface detail.
Even if they could make this work, the price will still be in the same range as
a Coronado or Dell Woods etalon filter.

Roland Christen