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Filters - L/R/G/B/Ha/OIII/SII/Hb/IDAS LP


Fordos Moon
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Afternoon All.

Soon I will be getting a 9 position filter wheel.

I have ZWO L/R/G?B filters already and intend to buy the Ha/OIII/SII and Hb filters.

Question is, while I have the wheel open is it worth sticking in an IDAS LP filter and what would I use this for when I am doing either LRGB or narrowband imaging with the other filters?

Many thanks

King of the Stupid Questions

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I have all my filters, LRGB and Ha / OIII stacked behind a 2" IDAS LP2 which is left in place for everything. Works wonders for my broadband imaging and doesn't effect the narrowband so I just leave it in place and forget about it.

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I have 9 filters in my EFW2 including the IDAS LP filter. I haven't opened it since installing them and there's no dust visible in flats from any filter.

I use LRGB when I have dark skies and LP RGB for normal use where I have some LP..

I don't use a LP filter in front of everything because it will cause some light loss even with the NB filters and every photon counts :)

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I don't use a LP filter in front of everything because it will cause some light loss even with the NB filters and every photon counts :)

You're not wrong there is a little loss due to the IDAS in front of narrowband filters, but it is an insignificant amount, the LP2 passes over 95% of Ha, OIII & SII and I see no difference in my images with very narrow 3nm pass band filters. But for the purest, you are of course correct, remove it from the light path and you'll gain that extra little bit back. :)

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I have an IDAS in series with my filter wheel too. If I was you I wouldn't bother with Hb - I've got one and never used it. It just gives the same signal as Ha but fainter.

Thanks Steve I did wonder of its purpose, FLO charge an extra £20 to have one included with the HA, OIII and SII package but i guess thats why its so cheap if it has little use could save myself twenty quid 

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Hb is a distinct wavelength at the other end of the spectrum to Ha, think Ha = red and Hb = blue.

There aren't a huge number of targets that emit much light in Hb, so I can see why these would be viewed as pretty much useless.  There's a list of targets here, the page refers to visual astronomy but I don't see why the list shouldn't be valid for imaging.

Saying that, I've never used mine :p

Cheers,

Ian

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