Can a OSC CCD not capture OIII & SII at the same time?

[Euan]

I've just been reading some of the pages on the Starizona website, especially this one about narrowband imaging:

Starizona's Guide to CCD Imaging

Within the bayer matrix of a OSC, OIII is a mixture of Green and Blue, and SII is purely Red.

Therefore, would it not be possible to use a multi-wavelength bandpass filter to capture a combination of Ha & OIII or SII & OIII at the same time? Each is separated in the bayer matrix anyway and could be split in processing

It would save loads of exposure time, and would actually give a wee edge to OSC over mono

Do standard light pollution filters not work like this anyway, just passing only specific wavelenghts or am I missing something?

[Merlin66]

No, your not missing anything other than the specialised filters needed!!

We can do exactly what you are askig for with the spectroscope!!

[SteveL]

Isnt that what a UHC filter does, only passing emission line wavelengths?

By contrast, light pollution filters pass everything and block specific wavelengths from streetlights.

[Euan]

The only UHC filters I've found are quite wide bandpass. Maybe it's not possible to combine 2 x 8nm filters in one?

[Merlin66]

I think the real problem is that no one has been asked to make such a mixture of narrow band filters.......

[Euan]

This is the closet thing I've found, the Hutech IDAS LPS-V3 Narrowband Nebula Filter, although it's pretty much just a UHC filter by the look of it

Hutech LPS-V3 IDAS Narrowband Nebular Filter - 2" - OPT Telescopes

[Tim]

Hmmm, now theres a thought! Given the bayer is 2 part green and 1 part blue, the OIII could be gathered just dandy i'd have thought at the same time as the Ha/ S2

[moocher]

Is this of any help Euan? U.K. Astronomy Buy & Sell

Alan:)

[Euan]

Is this of any help Euan? U.K. Astronomy Buy & Sell

Alan:)

Well spotted, now I'm really tempted just to see if it works

[blinky]

I looked at these filters before but could not figure out what they did! So..... Can somebody enlighten me? I looked at the website but it made no more sense to me!

[Merlin66]

OK, looking at the datasheets:

The UIBar is a UV-IR filter with cut-off wavelengths of 370nm and 680nm ( The Baader UV-IR filter for comparison is 400nm-700nm)

The LPS is a Light Pollution Supression filter which "effectively" cuts out light only from the annoying pollution light like high and low pressure Sodium lamps and Mercury lamps. The attached filter curve shows where it cuts off the light.

Hope this helps,

Ken

[SteveL]

Why does that AstroBuySell article have the users name as "Neil" in the description/text, but "Ian" in the email address? mmm...

[simon hicks]

I think this is simply a manufacturing issue.

The problem here is that you want three very narrow band filters in one coating run. This would be a very complex layer stack design requiring a great many layers, many more than you would need for a broader band UHC type filter. Also the coating precision would need to be much higher, requiring much more expensive coating equipment (maybe ion beam sputtering with in-situ optical monitoring), or yields would be lower.

Either way this probably makes such filters economically out of the reach of the amateur. However, it would be nice if a filter manufacturer would prove me wrong.

[Euan]

I've been having a think about this issue occasionally

Here is a good comparison of various filters used on M42. What I would really like to see is a comparison of the same types of filters used near a full moon, I suspect the individual narrowband filters will work much better. I would still opt for an LPS-V2 if the moon isn't up.

Filters on M42

[omneferuss]

I'm thinking the answer is that at those very narrow bands (typically 5-13nm ?) the emission-lines are emitted at vastly less intensity than the nearby general spectrum of stellar light... think of it as a red torch, a green torch & soforth.. beaming from among a barrage of 10,000 watt searchlights.

Afterall, we're looking for te re-emitted light frequencies of excited, but otherwise rather 'cool' matter in close proximity to humungous thermonuclear ultra-broadband electromagnetic generators.

The Bayer-matrix on a colour chip does not discriminate to any such degree as NB filters must.... Of the 16 million + colours your monitor screen displays, derived from just three colours of pixel (in an "emitting" matrix, but just like your colour-camera's "receiving/absorbing" Bayer-matrix ) how many do you suppose match that "green" emmission-line you want to capture ?? How many shades/hues of green can you think of ? ...take a walk in a garden or forest, or a paintshop while you ponder that

[Tim]

Euan, the OIII filters arent much use during full moon. The SII and Ha work great though, you can even get useable signal in twilight almost.

[riklaunim]

Well if you use few CCDs in a insane camera like this industry cams then it could be possible that one CCD gets O-III, and another on H-Alfa for example

[MartinB]

Thanks for that link to the IDAS filter Euan. It looks like a great filter to use for OSC on emission targets.