WTB: H-alpha Filter 1.25" or 2"
WTB: H-alpha Filter 1.25" or 2"
Not the solar type. Anyone has one for sale?
[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)]
Hi you can check out Astrobargains as he brings in Astronomik Halpha filters. Can't remember the bandpass but it should be on his website.
Photo Album:
http://www.flickr.com/photos/14113965@N03/
http://www.flickr.com/photos/14113965@N03/
Hi Tachyon,
Will you be using it with accompanying LRGB filters? Otherwise I would highly recommend Don Goldman's Astrodon filters. Most CCD imagers are using his filters. They are expensive, but you pay for what you get:
1) Parfocality. All filters were imaged through, require very little refocusing.
2) Bandpass wavelength limits are such that you only need to expose the same amount for each R, G, B component, instead of varying ratios.
3) Coated in such a way that internal reflections are minimized.
4) Halpha is available in two narrowband-pass widths. I have the 'narrower' one - 6nm. There is also a 'wider' one available.
The 6nm allows greater definition and contrast in the emissive nebula regons, however the tradeoff is lesser light throughput resulting in longer exposures for Halpha as compared to the 'wider' option. One of the pluses for imaging with the 6nm is moonlight is not much of a deterance, and you can theoretically image whole month around. I think this is important for us here in this region, especially when clear sky time is so precious. One disadvantage would be less likely to find suitable guidestars, which in this case, you will either guide with longer guide exposures (2 to 3 seconds each time round), or use a remote guide head, or alternatively, resort to using a separate autoguider.
Consequently, the 'wider' bandpass option would have the opposite points from the 6nm.
Personally, I would prefer not to lose nebula definition and minute structural details and thus went for the 6nm.
There are also other vendor choices from Astronomik, Custom Scientific, Baader Planetarium, and Barr Associates, but it seems that the Astrodons are very popular in the high-end and intermediate CCD imager market.
two cents!
Will you be using it with accompanying LRGB filters? Otherwise I would highly recommend Don Goldman's Astrodon filters. Most CCD imagers are using his filters. They are expensive, but you pay for what you get:
1) Parfocality. All filters were imaged through, require very little refocusing.
2) Bandpass wavelength limits are such that you only need to expose the same amount for each R, G, B component, instead of varying ratios.
3) Coated in such a way that internal reflections are minimized.
4) Halpha is available in two narrowband-pass widths. I have the 'narrower' one - 6nm. There is also a 'wider' one available.
The 6nm allows greater definition and contrast in the emissive nebula regons, however the tradeoff is lesser light throughput resulting in longer exposures for Halpha as compared to the 'wider' option. One of the pluses for imaging with the 6nm is moonlight is not much of a deterance, and you can theoretically image whole month around. I think this is important for us here in this region, especially when clear sky time is so precious. One disadvantage would be less likely to find suitable guidestars, which in this case, you will either guide with longer guide exposures (2 to 3 seconds each time round), or use a remote guide head, or alternatively, resort to using a separate autoguider.
Consequently, the 'wider' bandpass option would have the opposite points from the 6nm.
Personally, I would prefer not to lose nebula definition and minute structural details and thus went for the 6nm.
There are also other vendor choices from Astronomik, Custom Scientific, Baader Planetarium, and Barr Associates, but it seems that the Astrodons are very popular in the high-end and intermediate CCD imager market.
two cents!
Meng Lee - Thanks! That was my backup plan in case no ones wants to sell theirs! 
Remus - Thanks for the tip! 6nm sounds like the ideal I would like. Unfortunately, I do not have $400+ to blow on a filter now (all funds fully tied up for my scopes)! Plus, I do not have skills like yours to warrant a $400 filter! Heh... But I will definitely keep a lookout in Astromart!
Cheers!
Remus - Thanks for the tip! 6nm sounds like the ideal I would like. Unfortunately, I do not have $400+ to blow on a filter now (all funds fully tied up for my scopes)! Plus, I do not have skills like yours to warrant a $400 filter! Heh... But I will definitely keep a lookout in Astromart!
Cheers!
[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)]