I had a dumb idea...
solar telescopes are expensive because the etalon is expensive, and cost goes up exponentially with aperture, this is why solar telescopes are generally small.
Why isn't it possible to use a front white light solar filter, with an eyepiece HA filter, instead?
question about HA filters
-
orly_andico
- Posts: 1616
- Joined: Sun Aug 09, 2009 11:14 pm
- Location: Braddell Heights
- Contact:
-
orly_andico
- Posts: 1616
- Joined: Sun Aug 09, 2009 11:14 pm
- Location: Braddell Heights
- Contact:
eyepiece HA filters are cheaper than say a PST..
example:
http://www.optcorp.com/product.aspx?pid=2633
although I think I got it.. eyepiece filters are 6nm at best (60 Angstroms passband) while the solar HA filter is 0.8 Angstroms.
example:
http://www.optcorp.com/product.aspx?pid=2633
although I think I got it.. eyepiece filters are 6nm at best (60 Angstroms passband) while the solar HA filter is 0.8 Angstroms.
-
superiorstream
- Posts: 1501
- Joined: Mon Nov 03, 2008 4:45 pm
Hi,
The Ha filter for the sun is no ordinary filter.Its v. complicated.Firstly we have theDaystar type.It has to be pre-heated to achieve the necessary separation.The Science centre had it but I dont think it had produced any image for years. Note that these filter will degenerate with time and has to be sent back for repair.God knows if its still working.
Secondly we have the Colorado type.It consist of two parts--the energy reduction filter and the blocking filter.For the PST;I think both are combined inside the optical tube and hidden from view.The others are the solarmax filter sized--40mm;60mm or 90mm--well I heard of a 140 or 150mm but it a special order item and cost roughly equal to a HDB flat.For all these filter the front is the energy reduction filter--ERF--Its not just a simple filter glass but a thick piece consisting of a stack of red coloured ? filter that produce a series of highly separated diffraction red image of the sun.The bigger this block is the more expensive and its said some of these filters inside the block has separation of the order of nm.Next is the blocking filter consisting of a 'shining filter backed by a reddish pink filter--BF5mm;Bf10mm;BF15mm and Bf30mm for the SLR lovers.These filter--the shining park with DREAD RUST with time--Singapore takes 1-3 yrs to completely rust.You cant cut or do anything to these combination.
There are two more type--will continue next time.
The Ha filter for the sun is no ordinary filter.Its v. complicated.Firstly we have theDaystar type.It has to be pre-heated to achieve the necessary separation.The Science centre had it but I dont think it had produced any image for years. Note that these filter will degenerate with time and has to be sent back for repair.God knows if its still working.
Secondly we have the Colorado type.It consist of two parts--the energy reduction filter and the blocking filter.For the PST;I think both are combined inside the optical tube and hidden from view.The others are the solarmax filter sized--40mm;60mm or 90mm--well I heard of a 140 or 150mm but it a special order item and cost roughly equal to a HDB flat.For all these filter the front is the energy reduction filter--ERF--Its not just a simple filter glass but a thick piece consisting of a stack of red coloured ? filter that produce a series of highly separated diffraction red image of the sun.The bigger this block is the more expensive and its said some of these filters inside the block has separation of the order of nm.Next is the blocking filter consisting of a 'shining filter backed by a reddish pink filter--BF5mm;Bf10mm;BF15mm and Bf30mm for the SLR lovers.These filter--the shining park with DREAD RUST with time--Singapore takes 1-3 yrs to completely rust.You cant cut or do anything to these combination.
There are two more type--will continue next time.
I tried using a Mylar filter at the objective and a HA filter at the eyepiece from Edmund Scientific - did not work. All I got was a very dim red image. Furthermore, I was unable to tune the wavelength. Got a PST instead.
[80% Steve, 20% Alfred] ------- Probability of Clear Skies = (Age of newest equipment in days) / [(Number of observers) * (Total Aperture of all telescopes present in mm)]
-
superiorstream
- Posts: 1501
- Joined: Mon Nov 03, 2008 4:45 pm
....Continue....
Thirdly we have a type with a simple ERF-just a plane red filter.The second component is put infront of the eyepiece and contain a tuning knob.These filter combination usually has wide bandwith of 0.9A-1A or larger and suitable for prominences viewing only.Worse still tuning these filter is v.difficult and require infinite patiences.
Finally we have the Lunt type of arrangement where the ERF is inside the scope itself with the blocking filter outside.
As you can see its very very difficult to achieve the bandwidth needed for viewing solar surface feature--must be less than 0.7A.Above that you can only see prominences(0.9-1.2A)Anything above that is useless.Thus for example after the solarmax grating type of ERF which produce a selected series of Ha images,we need a blocking filter to further cut down the bandwidth to 0.7A.If after the ERF you just put a red filter,you cant see any prominences-not to mention solar surface features.Thus no ordinary filters including Ha filters for night sky photography can replace these filter combination(which work as a system).;and in turn also defy any modifications.
Thirdly we have a type with a simple ERF-just a plane red filter.The second component is put infront of the eyepiece and contain a tuning knob.These filter combination usually has wide bandwith of 0.9A-1A or larger and suitable for prominences viewing only.Worse still tuning these filter is v.difficult and require infinite patiences.
Finally we have the Lunt type of arrangement where the ERF is inside the scope itself with the blocking filter outside.
As you can see its very very difficult to achieve the bandwidth needed for viewing solar surface feature--must be less than 0.7A.Above that you can only see prominences(0.9-1.2A)Anything above that is useless.Thus for example after the solarmax grating type of ERF which produce a selected series of Ha images,we need a blocking filter to further cut down the bandwidth to 0.7A.If after the ERF you just put a red filter,you cant see any prominences-not to mention solar surface features.Thus no ordinary filters including Ha filters for night sky photography can replace these filter combination(which work as a system).;and in turn also defy any modifications.