Ha Filters

[Tandum]

I'll be looking for a Ha filter soon and am a bit confused with the number of filters for sale. They appear to range anywhere from 3nm to 15 nm with the narrow ones costing the most, as you'd expect.

What bandwidth will produce the best results to mix with RGB out of a Canon and or a QHY camera? Anyone know?

[Ian Robinson]

Halpha is a definite wavelength 656nm., so as long as the bandwidth of the notch filter includes that wavelength, it shouldn't make a lot of difference except cutting off red and IR emissions from other sources other than Halpha.

The narrower the bandwidth , the longer the exposure needed.

Aren't the very narrow band Halpha more suitable for solar prominence observing ? (the very narrow bandpasses mean they either absorb or reflect most the light that falls on them)

[Tandum]

So your confused too :)

Optcorp have pages of them to choose from -> http://www.optcorp.com/ProductList.aspx?uid=319-327-1157-861

3nm filters for US$1055 :scared:

[Zuts]

Hi Tandum,

Firstly the Ha CCD filters you see should never be used for solar prominence observing, you would fry your eyeball if you tried.

In general what you are paying for is the narrowist window around the Ha frequency with the highest transmission. Narrow high transmission filters are difficult to make so are very expensive.

The narrower the filter does not really mean you have to image for longer as if the transmission is high all you really are getting is the Ha which is what you want. For example, the attached is a 10 minute sub using the Astronomic 6nm Ha CCD filter. 10 minutes through this filter gives me better data than 10 minutes without the filter.

I would say any Ha CCD filter with a bandpass of between 6 and 10 nm with a transmission in the ha of greater than 90% would be suitable for your needs.

I can recomend the Astronomic filter at 6nm, however Bintel are now selling a set of Orion filters where if you buy all three you get 7nm Ha, OIII, SII for about 450 AUD. I havnt tried these but they are reported to be quite good.

However if you note the transmission it is quoted at 90% whereas even the 13nm Astronomic Ha is quoted at over 97%. Still, for the price they are probably very good.

Cheers
Paul

[Ian Robinson]

I suppose so :D, not tried imaging in Halpha (yet) , might now I have a nice digital SLR , but the narrow band notch halpha filter will have wait a while I think.

I can think of a lot of things I would rather spend several hundred or a housand or so dollar on before that,.

[Tandum]

Cheers Zuts, That's what I needed. My hong kong guy has baader 7nm Ha filters, I'll check prices.

[edit] Don't worry, I won't be pointing my reflector at the sun, in fact it rarely sees daylight :)

[Suzy_A]

I've got a 2" 7 nm Baader and think it works well for deep sky stuff.

The solar Ha filters are less than 1 A (1 A= 0.1 nm, so a 7 nm is 70 A) and the good ones are 0.5 or even 0.2 A.

[jase]

Some info in which may help you in your quest.
http://www.iceinspace.com.au/forum/showthread.php?t=31926