This came up as a result of reading/thinking about narrow band imaging and I haven't been able to find an answer, even though it's probably astrophysics 101.
The number of photons that can be detected is proportional to the bandwidth of the signal.
So if you were pointing at a pure H-a source, how wide (in nm) is the signal source ?
I'm not asking about the filter, but the light coming from the nebula or whatever.
Steve,
The actual observed width of emission lines varies with the source.
Pressure, temperature etc. change the shape of the emission.
For discussion purposes, you could safely assume around 2A FWHM
Does that help?
The filter bandwidths available to the amateur reflect the technology and pricing.
The 3/7/12nm (30/70/120A) Ha bandwidth filters end up in the hundreds of dollars, but getting down to <10A and 1 to 2A pushes technology to multi element etalon type filters in the thousands of dollars!!
