"Why" are Hydrogen Alpha filters so expensive?

I'm just curious what in the process of making a hydrogen alpha filter -
makes them so expensive? Why would a plain solar glass filter be about
$100 - but the same size piece of glass for hydrogen alpha is a few thousand
bucks?

Or is this really more of a supply and demand type of thing? Is it just
that so few companies make these that they can get away with charging a
fortune for them? I could see charging more for them but by a factor of
20 - 40?

Just curious. And jealous of those who can afford one of these. :-)

Glenn

Because they can and people will pay for a peice of glass as they think it'
is sooooooo good (Not)

"Indianaradio" wrote in message
...
Because they can and people will pay for a peice of glass as they think
it'
is sooooooo good (Not)

Oh - I think they are "soooooooo good" - I just can't afford one and am
wondering why they are so expensive. I would dearly love to have one of
these but I can't see that happening until the price is under $300 - and I
don't see that happening either. If I won the lottery I would buy one at
the current price.

Glenn

Indianaradio wrote:

Because they can and people will pay for a peice of glass as they think it'
is sooooooo good (Not)



Because to make a filter narrow band enough to work, and also to be
temperature stable in passband is extraordinarily difficult ?

There ARE other methods - the oscillating slit spectrohelioscope is on
my projects list for the future, but what you gain versatility, you will
lose in size, and it isn't going to be cheaper.

Steve

Oh - I think they are "soooooooo good" - I just can't afford one and am
wondering why they are so expensive.

They are expensive because they are a notch filter at a very specific frequency
and they need to be very narrow band and have very good rejection out side of
H-alpha band. These filters are also quite large, lots of surface area. For
visual work, solar filters need to only pass 1 part in 100000 of the incident
light so an HAlpha filter must do much better than that at rejecting unwanted
frequencies while pass the specific frequency.

I believe Al M. of Sirius Optics has a scheme for making them more cheaply that
he hopes to perfect someday but even then these will not be cheap.

So, if you, Mr. Indianaradio or anyone else wants to jump and and make these
and sell em for less than Coronado does, you are more than welcome to.

jon

I don't know anything about the manufacturing process, but I can tell you
that I bought one and I find it to be a fantastic piece of equipment.
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. However, if you want one now, you'll have to pay the
price.

Al


"Glenn Mulno" wrote in message
...
I'm just curious what in the process of making a hydrogen alpha filter -
makes them so expensive? Why would a plain solar glass filter be about
$100 - but the same size piece of glass for hydrogen alpha is a few
thousand
bucks?

Or is this really more of a supply and demand type of thing? Is it just
that so few companies make these that they can get away with charging a
fortune for them? I could see charging more for them but by a factor of
20 - 40?

Just curious. And jealous of those who can afford one of these. :-)

Glenn

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

"Glenn Mulno" wrote in message
...
I'm just curious what in the process of making a hydrogen alpha filter -
makes them so expensive? Why would a plain solar glass filter be about
$100 - but the same size piece of glass for hydrogen alpha is a few
thousand
bucks?

Or is this really more of a supply and demand type of thing? Is it just
that so few companies make these that they can get away with charging a
fortune for them? I could see charging more for them but by a factor of
20 - 40?

Just curious. And jealous of those who can afford one of these. :-)

Glenn
It is because of just how narrow the notch has to be. In 'audio' terms, this
would be a filter, that would not just seperate two 'notes', but even a tiny
tuning error on an instrument, probably inaudible to the ear, would take the
note outside the passband. It is probably one of the narrowest band filters
created for any application. To get the band this narrow requires the optics
to be made to the same sort of accuracies.
There are two basic 'types' of filter involved. The first is a simple 'dyed
glass' filter. These are the cheapest filters to make, and are the basis of
most simple 'colour' filters. The second is an interference filter. This is
much more expensive, (with the cost rising with accuracy). The most
expensive and accurate form of interference filter, is the Fabry-Perot
Etalon, which is the system used in the Ha filter assemblies. Unfortunately
to make this work at the right frequency, requires two optical surfaces, to
be ground with a spacing accurate to a tiny fraction of the wavelength of
light, and flat to the same sort of levels. It represents probably the most
accurate piece of optical equipment in 'mass production'. The normal solar
'filter', is simply a partially reflective surface (rather than being a
'bandpass' filter at all), but with the base material selected to also block
UV & IR to some extent.
Small Ha filters, are not that silly in price, and can give truly remarkable
solar images. Though the small size will limit the ultimate detail, an
enormous amount can be seen through these devices.

Best Wishes

-- "C" == Chris1011 writes:

C ..... The level of accuracy required to make etalon plates makes them
C very expensive.

What about an ATM approach ? I know etalon filters are expensive, but
our club already owns a 0.7 Å H-alpha filter which is basically made
with an ERF (IR-cut, heat-proof filter + W25 filter + negative lens to
obtain a longer f/ratio and to extract focus) followed by a cascade of
etalons in number variable depending on the desired bandwidth: about
0.8-1 Å with two filters, 0.7 Å with three, 0.5 Å with five; if I
remember well, each filter has a 2 Å bandwidth. "Tuning" is achieved by
tilting each filter in its seat.

This image:

http://www.gest.unipd.it/~jake/astro...un20032510.jpg

shows what I was able to do with the above filter (not that it looks
very well in front of other H-alpha imagers like Paul Hyndman, Thierry
Legault and Andy Chatman...).

I was looking for sources of other etalon plates, but it looks like I'm
not quite "in the market" (i.e.: I was not able to find anyone) for this
kind of supplies. Could you (or other SAA subscribers) point me to some
etalon makers ?

Regards,
Luca Polo.
--
Luca.Polo @ gest.unipd.it
Associazione Astrofili del Basso Vicentino "Edmund Halley"
http://halley.astrofili.org -- http://digilander.iol.it/aabv
e-mail:

Steve@home wrote:
: Indianaradio wrote:

That's what I'm waiting for, a spectrohelioscope that small enough to be practical. Questar has developed a spectrometer, and they were trying to make an
addition to make it a spectrohelioscope. Don't know where that project
went though. May be dead in the water.

:Because they can and people will pay for a peice of glass as they think it'
:is sooooooo good (Not)