H alpha Filters. which is best and why

[Alchemy]

Scouting around for H-Alpha filters for imaging, shows Baader, Lumicon and Astronomic all make versions.... with differing Bandpasses and PRICES. Point me in the right direction .

Thanks Clive.

[Merlin66]

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.

[Alchemy]

Thanks for the info. it will be used for DSO not solar, i wondered whether it was worth paying 449 for the narrowpass Astronomik versus 200 for the lumicon or baader vesions with a wider pass. Anyone got examples of either so i could see the difference.

[seeker372011]

The lumicon cannot be used with refractors-it allows all the IR in, you get bloated stars and so on. The japanese use this with an IR filter I am told but I have tried it and didnt think it worked, but hey I could be wrong.

If you are not convinced I can sell you mine (Lumicon night sky H alpha 1.25 inch) real cheap,

The Baader is highly recommended.And let me let you into a little secret. If you buy from OPT you can get the Baader 7nm 2 inch heaps cheaper than you can buy an astronomik in Australiai. OPT customer service was superb.

Richard Crisp who I believe knows a heck of a lot more about narrow band imaging than I do has done a review of the Baader against more expensive filters and reckons it stands up very well. I' ll see if I can find the link.. this was a year or so ago.
Narayan

[jase]

I think Narayan is referring to these:
http://www.narrowbandimaging.com/comparsion_of_ha_filters_page.htm
http://www.narrowbandimaging.com/filter_compare_astrodon_cust_sci_pa ge.htm

I've provided plenty of input into Ha filters in the past on these forums so will not repeat it again. A search will reveal them. Of course happy to provide assist if required.

[Alchemy]

Thanks for the replies, have done a search, as suggested and found these with some links embedded in them

http://www.iceinspace.com.au/forum/showthread.php?t=31029&highlight=narrowband

http://www.iceinspace.com.au/forum/showthread.php?t=28505&highlight=narrowband

plenty of reading to do......

no further info required .... thanks for all input.


clive.