Question about H-alpha Imaging

Hi all. I have tried a couple of times to image with my Custom Scientific H-alpha filter (4.5nm) without much success. It seems that so little light gets through the filter that I can't get a guide star to use without going to a really long exposure on the guider. Is it possible to autoguide with this type of filter? Would getting a 10nm filter (Schuler maybe?) make a big difference? Do most people who are doing H-alpha use a dedicated guide scope and guider in addition to the primary imaging scope? Any input would be appreciated.
Thanks and Cheers,
Tyler

Hi Tyler,

Not likely, probably and yes .

A 4.5nm filter gives you a very true H-alpha image but it diminishes star light so much that it not only makes it almost impossible to acquire guide stars, but it is also best for high QE NABG cameras like the ST7, 8, 10 and 6303. You might be able to guide with the 10nm but I have an ST2000XM and use an Astronomik 15nm with relatively good guiding results.

Mind you that as you open up the bandwidth you get less of a pure H-alpha signal but 15nm is still quite narrow - the SBIG Red filter is 58nm wide, for example.

Best,

Jose Suro
Tierra Verde, Florida

You either need a guide scope or a very accurate mounting so you can do unguided imaging. Another requirement would be a fast telescope - F4 to F6 if possible. Otherwise you get almost no signal.

Roland Christen