Radar
July 7th, 2007, 05:05 PM
Was thinking about filters earlier. Why do some Hydrogen Alpha filters allow you to see the sun and others deep space objects. What I mean is, if both filters are supposed to only allow you to see one part of the visible light spectrum, and they are supposed to both show HA, then why the two completely different fields?
It crossed my mind so I thought I'd ask.
Ray
Tony Leece
July 7th, 2007, 09:35 PM
My way of thinking on this Ray (forgive me if i'm way off) is all about intensity of light.
Your solar filter or telescope is geared to exclude +99% of all light from the sun using an 'ER' component, the Deep sky Ha filter has no need of an 'ER' (Energy rejection) component, because the light from distant stars and nebulae is so faint.
Hope i haven't made a complete tit of myself here, but this is how i have understood the differences :hmm:
All the best.......
Tony..........
AstroTasmania
July 8th, 2007, 09:25 AM
Hi Ray.
Tony is basically right. To access the very narrow band for solar work requires a "filter" which has something like 50 high tolerance dielectric coating to exclude everything except H-alpha at 6563 Angstrom. The "Filter" also contains many other filters to polarise the incoming light and eliminat UV & IR. To be able to see disc and prominence details one needs a H-alpha "filter" at about 0.6 A. If we take red to blue light, it is about 4000 to 8000 A, we need to get to the 0.5 A bit. All very expensive technology, expensive to produce to the fine tolerences. The low cost Coronado PST ($900) and Solarmax Scopes up to $12,000, are in the amateur price range, while the H-alpha pro observatory Zeiss models are up in the $75,000 range.
On the other hand, the simple low cost $100 red filter (dyed or interference) passes only a broad H-alpha band and is used on dark skies, not the sun, is totally innadequate for solar H-alpha work, and using such a filter would very quickly do a lot of damage.
I have several H-alpha solar devices, each have their application. A Lumicon H-alpha filter Etelon with energy rejection filters (UV & IR) & $1200?, (bright prominences only) Coronado 40 mm BF10 system & $2200 (Disc detail & Prominences), Baader Solar Coronograph Mark IV with occulting cones and two H-alpha filters at 1.5 & 0.6 Angstrom, $5,000 plus, (Prominences only)
Coronado PST, my quick look see scope with limited range).
My Picasa Album (link below) has pics of these in the Miscellaneous Folder.
Log on to Google and read about Lyot and Baader H-alpha filters - it will explain it a lot more than I can in a few simple terms.
Clear skies...
Shevill