24418RE: [ccd-newastro] H-alpha filters
- Mar 1, 2004Both of those are fairly wide-band filters. They will let in Ha, but they
will also let in light that is near Ha. This will reduce the contrast of the
Ha features, and it will also make all of the stars brighter.
Personally, I prefer a narrowband filter, maybe in the 3-5nm range. This
cuts out other bandwidths and provides better contrast, and stars are
greatly reduced which allows the nebula to stand out. But a narrowband
filter comes at some cost: it also lets in somewhat less Ha, too. A narrow
filter might allow 70-80% of the Ha through; a wider filter will allow
To me, the drop in Ha (say from 90 to 75 on average) is well worth the drop
The New CCD Astronomy Book
From: David Morris [mailto:dmorris99us@...]
Sent: Monday, March 01, 2004 8:58 AM
Subject: [ccd-newastro] H-alpha filters
Can anyone tell me the practical differences
between a 10nm bandpass H-alpha filter and a 13nm
bandpass one? What are the pros and cons, or is there
really much difference?
I'm imaging with an ST-8E through anything from an
Orion Short-tube 90 to a 10" LX200.
Thanks for any comments,
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