"Why" are Hydrogen Alpha filters so expensive?

"Dan McShane" wrote in message
...

"Roger Hamlett" wrote in message
...

Roger,

It`s very important to note that colored glass broadband filters use
organic
dyes that break down with UV exposure. Anyone out there contemplating an
ATM
H-alpha filter should avoid colored glass, at least as far as the
prefilter
is concerned.

Dan McShane
Yes. I would not want to use any of these filters directly in a 'solar'
path. I was purely trying to point out why there is such a large just from
the first 'filter' stage, to the next designs.
A good 'caveat'.

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.
Best Wishes

In message , Dan McShane
writes

"Roger Hamlett" wrote in message
...

Roger,

It`s very important to note that colored glass broadband filters use organic
dyes that break down with UV exposure. Anyone out there contemplating an ATM
H-alpha filter should avoid colored glass, at least as far as the prefilter
is concerned.

Not all coloured glass filters are organic dye based. Ionically and
colloidally coloured glasses also exist and are used for scientific
filters and church windows.

I haven't tested my H-alpha ERF prefilter, but it looks to me like it is
an optically flat low pass filter from colloidally coloured glass
something like Schott RG630 coated with an IR rejection layer. These red
glasses give very good rejection of short wavelengths.

The etalon appears to be sandwiched with a bluish Schott BG38? ionically
coloured glass again with an overcoated IR rejection filter. I presume
this is needed to bring down the power in the near IR and protect
delicate surfaces. That's what it looks like - but looks may be
deceiving

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.

It would be a very bad idea to rely on any organic dye based filters in
strong sunlight. Many organic dyes leak dangerous amounts of IR.

Regards,
--
Martin Brown

"Martin Brown" wrote in message
...
In message , Dan McShane
writes

"Roger Hamlett" wrote in message
...

Roger,

It`s very important to note that colored glass broadband filters use
organic
dyes that break down with UV exposure. Anyone out there contemplating an
ATM
H-alpha filter should avoid colored glass, at least as far as the
prefilter
is concerned.

Not all coloured glass filters are organic dye based. Ionically and
colloidally coloured glasses also exist and are used for scientific
filters and church windows.

Hi Martin,

I was referring mostly to slow rolloff longpass filters such as Schott
RG-600`s. As long as the dye is after the prefilter (that is with a neutral
density and/or longpass film as the first rejection surface), these filters
are fine.

About 12 years ago I built a "home brew" Ha filter when working for a thin
film company (Optical Corporation of America).
My boss allowed me to come over several weekends to do the coating runs. The
company`s baby at the time was a patented ion-assisted depostion process
called "micro-plasma". This was, at the time, the forerunner of most modern
IAD processes. The thermal stability of the film was 4-5 better than
traditional soft or hard film coatings. That quality also enabled ultra
narrowband filters to possess much greater TX% than traditional films.
This same technology is now used to make the ultra narrow filters used in
WDM (Wavelength Division Multiplexing) devices used in the fiber optic
communciation network(s).

Without much trouble we were able to get (10-12) 1.1 angstrom bandpass
filters. Using 2 filters in series I was able to tune them to get pretty
nice views of prominences and some surface features. I used a longpass,
shortpass, neutral density filter as the prefilter.

I haven't tested my H-alpha ERF prefilter, but it looks to me like it is
an optically flat low pass filter from colloidally coloured glass
something like Schott RG630 coated with an IR rejection layer. These red
glasses give very good rejection of short wavelengths.

The etalon appears to be sandwiched with a bluish Schott BG38? ionically
coloured glass again with an overcoated IR rejection filter. I presume
this is needed to bring down the power in the near IR and protect
delicate surfaces. That's what it looks like - but looks may be
deceiving

The blue appearance is actually due to the fact that most of the energy that
your eye perceives with that filter is in the blue portion of the VIS
spectrum. Even though the bandpass is centered in the red @656.3 the "raw"
narrowband energy is overwhelmingly blue to eye. This is the same reason
that some OIII filters appear red even though the BP is centered in the
blue.

Dan McShane

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.

It would be a very bad idea to rely on any organic dye based filters in
strong sunlight. Many organic dyes leak dangerous amounts of IR.

Regards,
--
Martin Brown


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Checked by AVG anti-virus system (http://www.grisoft.com).
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"Dan McShane" wrote in message ...


The blue appearance is actually due to the fact that most of the energy that
your eye perceives with that filter is in the blue portion of the VIS
spectrum. Even though the bandpass is centered in the red @656.3 the "raw"
narrowband energy is overwhelmingly blue to eye. This is the same reason
that some OIII filters appear red even though the BP is centered in the
blue.


Well, I'm afraid that this may not be the reason why some the Lumicon
OIII's tend to seem to be red. There are often two passbands found
with these filters; the primary one for the OIII lines and a secondary
"red leak" passband deep in the red. If you get a source which is red
enough, it will look red in the OIII, but if it has very little red
light, it will appear more bluish. I have used the OIII on M42 and
have been able to see some red in the outer regions of the nebula
using a 10 inch, so the "leak isn't exactly harmful, although most of
the time, its effect is not terribly noticable (except on the stars).
I have had fun with a few people when I put in a Carbon star in the
scope and stick in the Lumicon OIII. The star looks a bit like a red
Helium-Neon laser! :-). Some of the other OIII's do not have this red
secondary passband (the early Lumicon OIII's were this way), but
others sometimes do. Clear skies to you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 11th Annual NEBRASKA STAR PARTY *
* July 18-23, 2004, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************

Hi,
Actually, most colored glass filters use inorganic metal based dyes.
These are very hardy and don't break down. Most of these filters do
little in attenuating the IR.

Several years ago I developed a system where I was able to get laser
dyes into plastic. Many of these dyes have very strong IR rejection
well beyond the visual range. We have used these filters in military
night-vision applications. Some of these filters have gone into other
industrial uses. As with many glasses, this filter has very low UV
transmission. I would consider using these filters in a solar Ha
system. They are inexpensive enough to be replaced when needed.

Al M



Martin Brown wrote in message ...
In message , Dan McShane
writes

"Roger Hamlett" wrote in message
...

Roger,

It`s very important to note that colored glass broadband filters use organic
dyes that break down with UV exposure. Anyone out there contemplating an ATM
H-alpha filter should avoid colored glass, at least as far as the prefilter
is concerned.

Not all coloured glass filters are organic dye based. Ionically and
colloidally coloured glasses also exist and are used for scientific
filters and church windows.

I haven't tested my H-alpha ERF prefilter, but it looks to me like it is
an optically flat low pass filter from colloidally coloured glass
something like Schott RG630 coated with an IR rejection layer. These red
glasses give very good rejection of short wavelengths.

The etalon appears to be sandwiched with a bluish Schott BG38? ionically
coloured glass again with an overcoated IR rejection filter. I presume
this is needed to bring down the power in the near IR and protect
delicate surfaces. That's what it looks like - but looks may be
deceiving

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.

It would be a very bad idea to rely on any organic dye based filters in
strong sunlight. Many organic dyes leak dangerous amounts of IR.

Regards,

Al,

The easy solution is to be sure that the first surface on the rejection
filter is a 10% TX% ND, maybe a with a simple longpass rejecting from 280nm
400nm on top of the ND. Then your UV is already greatly reduced before any
other optical elements are involved.

Dan McShane

"Al M" wrote in message
m...
Hi,
Actually, most colored glass filters use inorganic metal based dyes.
These are very hardy and don't break down. Most of these filters do
little in attenuating the IR.

Several years ago I developed a system where I was able to get laser
dyes into plastic. Many of these dyes have very strong IR rejection
well beyond the visual range. We have used these filters in military
night-vision applications. Some of these filters have gone into other
industrial uses. As with many glasses, this filter has very low UV
transmission. I would consider using these filters in a solar Ha
system. They are inexpensive enough to be replaced when needed.

Al M



Martin Brown wrote in message
...
In message , Dan McShane
writes

"Roger Hamlett" wrote in message
...

Roger,

It`s very important to note that colored glass broadband filters use
organic
dyes that break down with UV exposure. Anyone out there contemplating
an ATM
H-alpha filter should avoid colored glass, at least as far as the
prefilter
is concerned.

Not all coloured glass filters are organic dye based. Ionically and
colloidally coloured glasses also exist and are used for scientific
filters and church windows.

I haven't tested my H-alpha ERF prefilter, but it looks to me like it is
an optically flat low pass filter from colloidally coloured glass
something like Schott RG630 coated with an IR rejection layer. These red
glasses give very good rejection of short wavelengths.

The etalon appears to be sandwiched with a bluish Schott BG38? ionically
coloured glass again with an overcoated IR rejection filter. I presume
this is needed to bring down the power in the near IR and protect
delicate surfaces. That's what it looks like - but looks may be
deceiving

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.

It would be a very bad idea to rely on any organic dye based filters in
strong sunlight. Many organic dyes leak dangerous amounts of IR.

Regards,


---
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Martin,
Are these red colloidal glass filters doped with gold?
Bill Bambrick
41 N, 73 W, 95 ASL

In message , Jb2269
writes
Martin,
Are these red colloidal glass filters doped with gold?

I'm not sure, but I think they are sulphide or selenide based.

Regards,
--
Martin Brown

Hi there Glenn. You posted:

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?

They are not just a simple "piece of glass", as such H-alpha filters are far
more complex than those needed for white-light viewing. The problem with
viewing in H-alpha is that the rest of the solar spectrum we see is incredibly
strong, nearly drowning out the fine H-alpha emissions of the Chromosphere.
Thus, so see the details in only the H-alpha emission line requires a *very
very* narrow bandwidth to completely screen out the other contaminating
wavelengths. A typical colored glass absorption filter might have a bandwidth
(Full-Width at Half-maximum) of 200 to 300 Angstroms. Some of the finer
nebula interference filters might have bandwidths around 50 to 100 Angstroms
or so. However, to see H-alpha detail merely on the limb requires a filter
bandwidth of only 1.5 Angstroms or less, and to see it clearly on the bright
solar disk requires a sharp bandwidth of *less than one Angstrom*. This
extremely-narrow bandwidth requirement clearly is filled only by a much more
critical and complex filter than one needed for just viewing sunspots.
These ultra-narrow filters are constructed a bit differently than even a
multi-layer interference filter. The heart of the DayStar and Coronado
filters is a Fabry-Perot etalon, a pair of partially-transmitting
plane-parallel plates with a close spacing which will allow the generation of
a series of very sharp and very narrow passbands. Blocking filters are then
used to eliminate the unneeded passbands, leaving only the H-alpha emission
passband. It is *very* difficult (and thus expensive) to produce such an
etalon to the quality required for solar H-alpha viewing, not to mention the
cost of the other components needed for the filter. These filters are often
very temperature sensitive, so the units which are placed near the focus of
the telescope often need critical temperature control in the form of an oven
(or the ability to "tilt" the filter stack to compensate for temperature
variations) The Coronado filters use an etalon out in front of the telescope,
but to get any significant aperture for viewing requires a *big* etalon, and
that further adds to the cost. Add to this the fact that these filters are
not exactly mass-produced in huge quantities and it is clear that the costs
for making the filters will be quite high.
That having been said, I do not regret saving for a few years and then
spending about $1800 for my DayStar T-Scanner, as it has opened up a whole new
world for me. Seeing the sun revealed in the light of H-alpha is an
incredible experience not soon to be forgotten. Clear skies to you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 11th Annual NEBRASKA STAR PARTY *
* July 18-23, 2004, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************

Hello, David,
I know it must take you a good bit of time to compose your posts, but they are
clear, thorough, and authoritative, and I want you to know that we appreciate
them and thank you for taking the time to write them.
Cordially,
Bill Meyers

David Knisely wrote:

Hi there Glenn. You posted:

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?

They are not just a simple "piece of glass", as such H-alpha filters are far
more complex than those needed for white-light viewing. The problem with
viewing in H-alpha is that the rest of the solar spectrum we see is incredibly
strong, nearly drowning out the fine H-alpha emissions of the Chromosphere.
Thus, so see the details in only the H-alpha emission line requires a *very
very* narrow bandwidth to completely screen out the other contaminating
wavelengths. A typical colored glass absorption filter might have a bandwidth
(Full-Width at Half-maximum) of 200 to 300 Angstroms. Some of the finer
nebula interference filters might have bandwidths around 50 to 100 Angstroms
or so. However, to see H-alpha detail merely on the limb requires a filter
bandwidth of only 1.5 Angstroms or less, and to see it clearly on the bright
solar disk requires a sharp bandwidth of *less than one Angstrom*. This
extremely-narrow bandwidth requirement clearly is filled only by a much more
critical and complex filter than one needed for just viewing sunspots.
These ultra-narrow filters are constructed a bit differently than even a
multi-layer interference filter. The heart of the DayStar and Coronado
filters is a Fabry-Perot etalon, a pair of partially-transmitting
plane-parallel plates with a close spacing which will allow the generation of
a series of very sharp and very narrow passbands. Blocking filters are then
used to eliminate the unneeded passbands, leaving only the H-alpha emission
passband. It is *very* difficult (and thus expensive) to produce such an
etalon to the quality required for solar H-alpha viewing, not to mention the
cost of the other components needed for the filter. These filters are often
very temperature sensitive, so the units which are placed near the focus of
the telescope often need critical temperature control in the form of an oven
(or the ability to "tilt" the filter stack to compensate for temperature
variations) The Coronado filters use an etalon out in front of the telescope,
but to get any significant aperture for viewing requires a *big* etalon, and
that further adds to the cost. Add to this the fact that these filters are
not exactly mass-produced in huge quantities and it is clear that the costs
for making the filters will be quite high.
That having been said, I do not regret saving for a few years and then
spending about $1800 for my DayStar T-Scanner, as it has opened up a whole new
world for me. Seeing the sun revealed in the light of H-alpha is an
incredible experience not soon to be forgotten. Clear skies to you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 11th Annual NEBRASKA STAR PARTY *
* July 18-23, 2004, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************