Which Ha filter ?

[johnb]

Hi

So using the kit in my signature I’m going to try adding Ha images (one day I will have a CCD) oh my Camera is Modded

So looking at the FLO site there are choices

H-alpha 7nm

H-alpha 35nm

H-beta 8.5nm (not sure what H Beta is)

I assume ideally I need the H-alpha 7nm filter (which obviously is the most expensive)

Regards

John B

[ollypenrice]

You certainly do! The wider ones are far less contrasty and much less effective against the moon. You can make the 7Nm from FLO feel much cheaper by looking at the price of the Astrodons...

H Beta is the second best emission line from ionized hydrogen. It usually gives far less signal but traces the same gasses and is blue in colour. In amateur hands it isn't widely used other than on the Horsehead.

Olly

[Sp@ce_d]

Yup. I use the 7nm with the 1000D. very happy with it.

[Martin-Devon]

You may want to look at the Astrodon H-alpha filter supplied by Ian King Imaging. Yes it costs a lot more than the Baader, but it's 5nM so will cut out even more unwanted background and moonglow - the Astrodon filters are arguably the best you can buy. I started off with the single H-alpha, and gradually over time purchased the OIII & SII filters as well.

[davew]

You may want to look at the Astrodon H-alpha filter supplied by Ian King Imaging. Yes it costs a lot more than the Baader, but it's 5nM so will cut out even more unwanted background and moonglow - the Astrodon filters are arguably the best you can buy. I started off with the single H-alpha, and gradually over time purchased the OIII & SII filters as well.

You should have told John to sit down first !

I wouldn't bother about Hb for imaging. If you read the description of the Hb CCD Astronomik on Ian King's site you'll see it starts off as an imaging filter and magically transforms into a visual filter. One trick that's sometimes used is to layer 20% or so of an Ha image onto an O111 layer. This cuts the Ha right down to Hb levels but keeps the stars reasonable.

Buy the best filters you can afford.

Dave.