GlassWalker

Another thing that occurs to me is that, I might be saying something stupid but, isn't it the case that the camera's software is programmed to run colour interpolation algorithms? Shouldn't that be having an effect on the quality of the pictures in the debayered sensor?

If you use the "colour" image directly from the camera, that is the case. But if you save the raw output, you can skip the colour conversion process and have the mono data directly.

Interesting stuff... in a quick look dichloroethane can be got from ebay, but it does sound a bit of a nasty chemical to have around! Still, this talk is making me want to have a go at this myself with whatever I have around at home.

By loss of resolution, I am talking about only 1/4 of the pixels being effective when using Ha or SII. A nominal 12MP colour camera is effectively 3MP when you put that filter on. It just seems a bit of a waste that 3/4 of the sensor is doing nothing useful. The reason anyone does that is any decent mono CCD is going to be quite a lot more expensive.

However, we might be looking too hard at resolution here. Most astro CCDs are relatively low MP count too. And of course the resolution will also depend on your optics and even the conditions if you push hard. Regardless of the sensor, if you feel lacking in resolution you can always go longer focal length, and if needed also mosaic frames to cover bigger subjects.

As a side note, I like using OIII more than Ha because more of the sensor is active in that case... but it does rather depend on the subject being rich in OIII in the first place.

Using a narrowband filter on a colour sensor is always going to be a compromise. I also use Astronomik 12nm filters on DSLR, but of course you're losing a large chunk of the sensor when doing that (particularly hits resolution). Last night I had another go at the horsehead and flame, this timg in Ha only. The moon was still quite full and close, and I think that pushed the background level too high even in Ha. Even my colour images of the same region had better contrast, but the moon wasn't out when I tried that. Maybe narrower ones will help more...

So you're saying a 15Mp colour cam is only 3.75Mp in resolution - don't think the maths works like that - if so then we've all been conned Surely the camera sensor uses two elements eg the luminance provides the image detail and dynamic range and chrominance adds blurred colour 'wash' which the eye find fully acceptable. Ok the bayered resolution can't be 100% but neither is it just 33%

Fundamentally bayer colour filter sensors do not sample all colours at all points, with the information interpolated to produce the nominal full resolution output. As a worst case scenario, the resolution is 25% of nominal! If you have a strongly red or blue subject, with little in the other channels, you're only significantly stimulating 25% of the detectors. e.g. using Ha filter on a bayer sensor, you're throwing away 75% of the sensor output. Removing that bayer filter would get you back to 100% again.

Unfortunately mono cameras where available (astronomical ones too) seem more expensive than their colour counterparts, so if we can remove the colour filter from a DSLR it would enable another level of lower cost imaging.

I don't know about DSS, but I think in many raw conversion processes there's an "ignore bayer" or similar option. I think PixInsight's raw conversion uses dcraw as a base, and that has an option to just convert without debayering. But I'm not sure where to find the options to do that in PI or other software.

Hmm... I think my 450D just gave me a nervous look! I have long wondered how hard would it be to remove the CFA, but never took it further... so if I understand correctly, you just need to try and remove the CFA layer without damaging or scratching the underlying surface? And in this case you used some kind of mild abrasive?

Actually, I might give this a go on my 300D IR mod as a test before I break the 450D

After that, just need to figure out how to configure software not to de-bayer a non-bayer...