|
Ha Filters
Generally there are two main applications for the Ha filters-
Solar work and DSO's
For solar work they have to be combined with an Energy Rejection Filter ( ERF) at the objective and be as narrow a bandwidth as you can get ( to improve contrast and resolution). The narrowest "standard" filter I've seen is about 5 to 7nm which is still too wide for effective solar work. You need to go to the specialised Day Star/PST/ Lunt etalon designs to get to < 0.1nm.
For hydrogen emission DSO's, Lumicon and others sell a Ha pass filter which just blocks any light below 600nm ( ie only allows Red/IR light to pass through) These are pretty good as a light pollution filter as well.
Other filters from 60nm to 5nm bandwidth only reduce the IR light getting to the camera and improve the contrast in Ha. The narrow band are usually only used where you want to build up a false colour 3 band image ( ie OIII/ SII/ Ha)
You should also be aware that it can be very difficult to focus the image through a Ha filter due to lack of light. Usual to focus with a plain filter of the same thickness and then changeover the filters.
Summary:
For solar you need specialised filters and an ERF
For Ha emission, general imaging a broadband would work well, for detailed contrast and 3 band work a narowband is required.
Hope this helps.
|