Astromart

January 31, 2005 10:22 PM Forum: CCD Imaging and Processing/Deep Sky

California Nebula

Once again Cal, very nice.

Tom Davis

February 3, 2005 03:20 PM Forum: CCD Imaging and Processing/Deep Sky

James,

H-alpha filters for deep sky imaging are similar to H-alpha solar filters in that they both isolate the very narrow Hydrogen-alpha portion of the spectrum. However, the filter that is designed for deep sky imaging SOULD NOT BE USED for solar viewing!! It will not block enough sunlight and severe eye damage can occur.

As far as the deep sky Ha filter, there are essentially three types or "Narrowness". These are 10nm, 6nm, and 3nm. The 10nm has a broader window and lets in more light so exposures can be shorter and guide stars can be found. The 3nm gives the most contrast between the object and the sky, but at a cost of longer imaging times and much fewer guide stars. A good compromise is a 6nm. Even though these filters can isolate the Ha bandwidth of the spectrum and give amazing results (like Larry pointed out in his post) you still need long exposure times or many shorter exposures stacked to overcome the signal to noise ratio. Short exposures times may show the object, but there will be a lot of noise when processed. Best to get a lot of exposure time.

I agree with Larry, if you are going to image emission nebulae then a high quality Ha filter is very necessary. These filters are available from Custom Scientific filters, Astronomik, Don Goldman Tru-Balance filters(my favorite), Lumicon and others.

Tom Davis
Inkom, ID

February 6, 2005 01:30 AM Forum: CCD Imaging and Processing/Deep Sky