h-alpha filters for imaging

[phatlad]

hi all

i'm slowly getting to grips with ccd imaging and have been thinking about getting a h-alpha filter as i believe (and please correct me if i am wrong) that i will be able to get some better deep sky images even with a moon about. my question is tho i have been looking at filters and seen that there is lots of types, 7nm, 35nm, what is the difference between them and what would be best for me?

thanks glen

[shaunster]

7nm would be the best, especially under a moon

the larger bandpasses, 35nm etc let through more background light but not more Ha light

[Andrew*]

Hydrogen alpha is light emitted by nebulae at 656 nm wavelenth. The light colour/wavelength is very specific, so ideally you want to isolate it as much as possible. A 7nm wavelength transmits a 7nm range of wavelengths centred on 656nm.

So basically, narrower wavelengths are more effective as they cut out more ambient light (starlight, moonlight, light pollution), but they are usually more expensive.

HTH

Andrew

[antimorris]

As Andrew said, the narrower the better and also the more expensive. I use an Astronomik 12nm Ha filter though I got it in a set with the L,R,G & B together. I have been perfectly happy with the 12nm and considering it is 3/4 the price of the 6nm I will probably stay with it.

[phatlad]

thanks for all the help. well i get paid on thursday so i think i will have a shop round and get myself either a 7 or 12nm filter if people are with them.

thanks again

glen

[ollypenrice]

I highly recommend the Baader 7Nm. I also have the 13 Astronomik, the first of which created haloes. The free replacement didn't but there is more contrast in the Baader and it is better in the moonlight.

Olly

[phatlad]

I highly recommend the Baader 7Nm.

i'm glad you said that olly i was looking at the 7Nm baader, and i will be ordering one on thursday

glen