didymium - sodium light buster + other filters

I've posted at http://home.freeuk.com/m.gavin/grism2.htm

some colour spectra via a digital camera showing the transmission of
various filters like...

TT RGB interference set showing red leak
Hoya CMY
didymium -sodium light buster
TV monitor, fluorescent, neon and energy saving lamps [emission lines]
and spectrum of daylight

all via a simple but effective homemade spectroscope. I'd appreciate
feedback.

Maurice Gavin - WPO - UK

Robin Leadbeater wrote:

"Maurice Gavin" wrote in message
...
I've posted at http://home.freeuk.com/m.gavin/grism2.htm
some colour spectra via a digital camera showing the transmission of
various filters like...
TT RGB interference set showing red leak
Hoya CMY
didymium -sodium light buster
TV monitor, fluorescent, neon and energy saving lamps [emission lines]
and spectrum of daylight
all via a simple but effective homemade spectroscope. I'd appreciate
feedback.
Maurice Gavin - WPO - UK
Hi Maurice,
Good to see someone else checking up on those filter claims ;-) I have been thinking about
getting a prism to improve my similar spectroscope. See
http://www.leadbeaterhome.fsnet.co.u...er_spectra.htm
Where did you get you prism from?
Regards
Robin

I have one (possibly two, will have to check) old prisms from an old pair of wrecked binocularss if
anyone wants it (them ?)

Nice work on both sites BTW !

DH
Telford

Robin Leadbeater wrote:

"Maurice Gavin" wrote in message
...
I've posted at http://home.freeuk.com/m.gavin/grism2.htm
some colour spectra via a digital camera showing the transmission of
various filters like...
TT RGB interference set showing red leak
Hoya CMY
didymium -sodium light buster
TV monitor, fluorescent, neon and energy saving lamps [emission lines]
and spectrum of daylight
all via a simple but effective homemade spectroscope. I'd appreciate
feedback.
Maurice Gavin - WPO - UK
Hi Maurice,
Good to see someone else checking up on those filter claims ;-) I have been thinking about
getting a prism to improve my similar spectroscope. See
http://www.leadbeaterhome.fsnet.co.u...er_spectra.htm
Where did you get you prism from?
Regards
Robin

I have one (possibly two, will have to check) old prisms from an old pair of wrecked binocularss if
anyone wants it (them ?)

Nice work on both sites BTW !

DH
Telford

On Sat, 12 Jul 2003 11:50:37 +0100, "Robin Leadbeater"
wrote:


"Maurice Gavin" wrote in message
...
I've posted at http://home.freeuk.com/m.gavin/grism2.htm

some colour spectra via a digital camera showing the transmission of
various filters like...

TT RGB interference set showing red leak
Hoya CMY
didymium -sodium light buster
TV monitor, fluorescent, neon and energy saving lamps [emission lines]
and spectrum of daylight

all via a simple but effective homemade spectroscope. I'd appreciate
feedback.

Maurice Gavin - WPO - UK


Hi Maurice,

Good to see someone else checking up on those filter claims ;-) I have been
thinking about getting a prism to improve my similar spectroscope. See

http://www.leadbeaterhome.fsnet.co.u...er_spectra.htm

Where did you get you prism from?

Regards
Robin

Nice site Robin - I should visit uk.sci.astronomy more ofteng.
Grism eg combined weak prism + trans grating on one surface to give a
'straight-through' view been in the junk box for years source unkown
but probably from a 1890's prom scope.

Without the prism the spectrum from the grating is angled to the side
so either the slit or tube carrying it must be offset slightly - but
you knew thatg.

Maurice

On Sat, 12 Jul 2003 11:50:37 +0100, "Robin Leadbeater"
wrote:


"Maurice Gavin" wrote in message
...
I've posted at http://home.freeuk.com/m.gavin/grism2.htm

some colour spectra via a digital camera showing the transmission of
various filters like...

TT RGB interference set showing red leak
Hoya CMY
didymium -sodium light buster
TV monitor, fluorescent, neon and energy saving lamps [emission lines]
and spectrum of daylight

all via a simple but effective homemade spectroscope. I'd appreciate
feedback.

Maurice Gavin - WPO - UK


Hi Maurice,

Good to see someone else checking up on those filter claims ;-) I have been
thinking about getting a prism to improve my similar spectroscope. See

http://www.leadbeaterhome.fsnet.co.u...er_spectra.htm

Where did you get you prism from?

Regards
Robin

Nice site Robin - I should visit uk.sci.astronomy more ofteng.
Grism eg combined weak prism + trans grating on one surface to give a
'straight-through' view been in the junk box for years source unkown
but probably from a 1890's prom scope.

Without the prism the spectrum from the grating is angled to the side
so either the slit or tube carrying it must be offset slightly - but
you knew thatg.

Maurice

On Sat, 12 Jul 2003 11:22:16 +0100, "Kev"
wrote:


"Maurice Gavin" wrote in message
...
I've posted at http://home.freeuk.com/m.gavin/grism2.htm

some colour spectra via a digital camera showing the transmission of
various filters

all via a simple but effective homemade spectroscope. I'd appreciate
feedback.

FWIW I think that if you could get hold of various filters and publish them
on a page like this - from various friends and local society members then
you could be very popular with amateur astronomers and very unpopular with
some brands of filter makers !

regards, Kev

Kev - yes something for the autumn when societies return from the
summer break. I'm sure makers will be interested in the independent
'truth' - the TT IF don't seem to pass yellow so if you have LP sodium
skyglow it should be noticeably suppressed via TT RGB imaging.
Maurice

On Sat, 12 Jul 2003 11:22:16 +0100, "Kev"
wrote:


"Maurice Gavin" wrote in message
...
I've posted at http://home.freeuk.com/m.gavin/grism2.htm

some colour spectra via a digital camera showing the transmission of
various filters

all via a simple but effective homemade spectroscope. I'd appreciate
feedback.

FWIW I think that if you could get hold of various filters and publish them
on a page like this - from various friends and local society members then
you could be very popular with amateur astronomers and very unpopular with
some brands of filter makers !

regards, Kev

Kev - yes something for the autumn when societies return from the
summer break. I'm sure makers will be interested in the independent
'truth' - the TT IF don't seem to pass yellow so if you have LP sodium
skyglow it should be noticeably suppressed via TT RGB imaging.
Maurice

In message , Maurice Gavin
writes
I've posted at http://home.freeuk.com/m.gavin/grism2.htm

some colour spectra via a digital camera showing the transmission of
various filters like...

TT RGB interference set showing red leak
Hoya CMY
didymium -sodium light buster
TV monitor, fluorescent, neon and energy saving lamps [emission lines]
and spectrum of daylight

all via a simple but effective homemade spectroscope. I'd appreciate
feedback.

That's a very nice way to display higher resolution spectra. How did you
get the colour spectrum to be a decent rendition in colour? My digicams
(and colour films for that matter) baulk at giving an accurate coloured
representation of the monochromatic light at different wavelengths in a
spectrum.

I should declare an interest here, since I sell a neodymium doped glass
filter, Nonad, as a sideline. Info and low resolution spectra at:

http://www.nezumi.demon.co.uk/nonad/nonad.htm

The didymium filter you used looks to be less dense than Nonad. Was it a
Baader or one of the other possible commercial didymium glasses?

For completeness you might consider also doing one of the standard US
broadband LPRs (optimised for mercury light) and the Orion UK sodium
light filter which is about as good as you can get visually for mixed
HPS and LPS lighting environments. If more people could see independent
assessments of these filters they might buy the right ones.

If any filter deserves to be called the sodium light buster it is Orion
UKs.

Didymium or neodymium glass like Nonad is only effective against the
nearly monochromatic orange-yellow low pressure sodium lights. Then it
works well, but the effect is still quite subtle visually. Look at the
spectral absorbtion lines and you will see why. It is most effective
photographically when it delays the onset of sky fog and keeps it a more
neutral black for considerably longer exposures in suburban
environments.

I found the spectrum of the near IR leak on TTs R+B a bit confusing at
first, but to be fair to TT you should perhaps give some indication of
how much longer the exposure has to be for that image compared to the
others.

The leak isn't obvious on the normal spectral exposures.
I presume TT R+B is a much longer exposure?

Another light source that has a very interesting detail spectrum is an
HPS lamp - self absorbed on the sodium D-lines and an odd turquoise
emission line smack bang in the middle of the OIII narrow line filter
passband.

Even the humble low pressure sodium lamp has some other faint spectral
emission lines that should show nicely in your setup.

Regards,
--
Martin Brown

In message , Maurice Gavin
writes
I've posted at http://home.freeuk.com/m.gavin/grism2.htm

some colour spectra via a digital camera showing the transmission of
various filters like...

TT RGB interference set showing red leak
Hoya CMY
didymium -sodium light buster
TV monitor, fluorescent, neon and energy saving lamps [emission lines]
and spectrum of daylight

all via a simple but effective homemade spectroscope. I'd appreciate
feedback.

That's a very nice way to display higher resolution spectra. How did you
get the colour spectrum to be a decent rendition in colour? My digicams
(and colour films for that matter) baulk at giving an accurate coloured
representation of the monochromatic light at different wavelengths in a
spectrum.

I should declare an interest here, since I sell a neodymium doped glass
filter, Nonad, as a sideline. Info and low resolution spectra at:

http://www.nezumi.demon.co.uk/nonad/nonad.htm

The didymium filter you used looks to be less dense than Nonad. Was it a
Baader or one of the other possible commercial didymium glasses?

For completeness you might consider also doing one of the standard US
broadband LPRs (optimised for mercury light) and the Orion UK sodium
light filter which is about as good as you can get visually for mixed
HPS and LPS lighting environments. If more people could see independent
assessments of these filters they might buy the right ones.

If any filter deserves to be called the sodium light buster it is Orion
UKs.

Didymium or neodymium glass like Nonad is only effective against the
nearly monochromatic orange-yellow low pressure sodium lights. Then it
works well, but the effect is still quite subtle visually. Look at the
spectral absorbtion lines and you will see why. It is most effective
photographically when it delays the onset of sky fog and keeps it a more
neutral black for considerably longer exposures in suburban
environments.

I found the spectrum of the near IR leak on TTs R+B a bit confusing at
first, but to be fair to TT you should perhaps give some indication of
how much longer the exposure has to be for that image compared to the
others.

The leak isn't obvious on the normal spectral exposures.
I presume TT R+B is a much longer exposure?

Another light source that has a very interesting detail spectrum is an
HPS lamp - self absorbed on the sodium D-lines and an odd turquoise
emission line smack bang in the middle of the OIII narrow line filter
passband.

Even the humble low pressure sodium lamp has some other faint spectral
emission lines that should show nicely in your setup.

Regards,
--
Martin Brown

On Tue, 15 Jul 2003 09:09:32 +0100, Martin Brown
wrote:

In message , Maurice Gavin
writes
I've posted at http://home.freeuk.com/m.gavin/grism2.htm

some colour spectra via a digital camera showing the transmission of
various filters like...

TT RGB interference set showing red leak
Hoya CMY
didymium -sodium light buster
TV monitor, fluorescent, neon and energy saving lamps [emission lines]
and spectrum of daylight

all via a simple but effective homemade spectroscope. I'd appreciate
feedback.

Ahhhhhhh - Kev judge this subject matter well !!!

That's a very nice way to display higher resolution spectra. How did you
get the colour spectrum to be a decent rendition in colour? My digicams
(and colour films for that matter) baulk at giving an accurate coloured
representation of the monochromatic light at different wavelengths in a
spectrum.

Never had problems with colour spectra - been doing it for some years.

I should declare an interest here, since I sell a neodymium doped glass
filter, Nonad, as a sideline. Info and low resolution spectra at:

http://www.nezumi.demon.co.uk/nonad/nonad.htm

The didymium filter you used looks to be less dense than Nonad. Was it a
Baader or one of the other possible commercial didymium glasses?

No - it was a sample from an ophthalmatist used, so I understand, in
some prescription glasses

For completeness you might consider also doing one of the standard US
broadband LPRs (optimised for mercury light) and the Orion UK sodium
light filter which is about as good as you can get visually for mixed
HPS and LPS lighting environments. If more people could see independent
assessments of these filters they might buy the right ones.

Agreed. Will be pleased to receive samples including Nonad for
testingg.

If any filter deserves to be called the sodium light buster it is Orion
UKs.

Didymium or neodymium glass like Nonad is only effective against the
nearly monochromatic orange-yellow low pressure sodium lights. Then it
works well, but the effect is still quite subtle visually. Look at the
spectral absorbtion lines and you will see why. It is most effective
photographically when it delays the onset of sky fog and keeps it a more
neutral black for considerably longer exposures in suburban
environments.

I found the spectrum of the near IR leak on TTs R+B a bit confusing at
first, but to be fair to TT you should perhaps give some indication of
how much longer the exposure has to be for that image compared to the
others.

The leak isn't obvious on the normal spectral exposures.
I presume TT R+B is a much longer exposure?

Somewhat longer but not excessively so - the unfiltered sample of
daylight is at the top - the filter only covers the lower half of the
slit in a single exposure. The red leak is at~7000A and an IR block
filter suppresses it and longer wavelengths remembering that some [non
Starlight Xpress - Sony camcorder chips] CCDs typically peak ~7000A.

Another light source that has a very interesting detail spectrum is an
HPS lamp - self absorbed on the sodium D-lines and an odd turquoise
emission line smack bang in the middle of the OIII narrow line filter
passband.

Even the humble low pressure sodium lamp has some other faint spectral
emission lines that should show nicely in your setup.

Yes - I've done LPS [its outside my house!] and will post shortly and
maybe HP sodium too although luckily none are nearby. Just feel a
little conspicuous aiming my devise at street lampsg.

Maurice Gavin

Regards,
--
Martin Brown