OIII filters

[Ant]

I've read that people use an OIII fitler to cut through excessive moon light. I use a dSLR (unmodded), would there be any advantage of using a OIII filter with the ED80 and dSLR?

Would you have to use a LPR filter in addition to the OIII filter or does the fact that you are imaging in a narrow band of light effectivly remove the need for the LPR filter.

And lastly what objects are not suitable/more suitable for the OIII filter

Cheers

Ant

[narrowbandpaul]

you wouldnt have to use an LPR since the predominant Na emission falls at 589nm...well outside the band allowed by even the broadest O[iII] filter.

It would make sense, and I think that it may be unavoidable, to use one that passes Hbeta at 486nm also. O[iII] is a doublet at 498/500.7nm. Inclusion of Hbeta is good for two reasons...

First of all, it has the same spatial distribution as Ha light, since the emission is still coming from Hydrogen...so it picks up the bluer 'Ha' light in effect.

Secondly, your chip (and eye) like this bluey green light. Even though the Ha is 2.92x the intensity of Hbeta, your Camer's QE at Hb is more than 2.92x than at Ha...so you camera picks up Hbeta better than Ha.

Now...O[iII] is a particularly predominant wavelength in planetary nebula, since they are illuminated by a hot White dwarf. Further, O[iII] is actually more intense than Ha for these planetary nebula.

So objects illuminated by a hot star should be a good choice...PN's, wolf rayet (bubble neb crescent neb)

Believe it or not, I find O[iII] a poorer wavelength than S[iI]...there isnt too much O[iII] in the world as it only maps High energys.

However, it is still nice...

Hope this helps

paul

[Talitha]

And lastly what objects are not suitable/more suitable for the OIII filter

Cheers

Ant

Hi Ant, here's the best filter comparison list I've ever seen... hope it's what you were looking for.

Filter Performance Comparisons For Some Common Nebulae By David Knisely