DSLR and Narrowband

[johnb]

Hi

Its been discussed on the forum before but I could not find all the answers so here goes.

I see you can get NB filters (and others) for DSLRs but I also see you can actually attach filter wheels to the camera.

So on the kit side does anyone do this and if so what filter wheel do they use ?

So assuming you use filters how does the process go, I assume RGB are actually combined and then you just add the Narrow Band exposures much in the same way as you would when CCD imaging ?

Regards

John B

[Shibby]

Hi John,

Yeah, the NB filters are the same ones you would use for a dedicated camera. I use an Ha filter but not in a filter wheel, just the 2" version screwed onto the end of my coma corrector. As your DSLR is an OSC (one-shot colour), the RGB data can be taken in one go without a filter (other than a light pollution filter).

With narrowband filters (Ha in particular) you are only using 1 pixel out of 4 in the bayer matrix, so your resolution is effectively divided by 4. I stack my Ha subs using "super pixel" mode, then just delete the G + B channels.

As for combining the data sets, there are many different methods with different sorts of results. I can't tell you which are best...

[johnb]

I stack my Ha subs using "super pixel" mode, then just delete the G + B channels.

Thanks for the info can I do the above in DSS ?

John B

[Shibby]

Yep, it's in the RAW settings.

[johnb]

Thanks can wait, have posted some images where you have combined RGB and Ha using this method.

Regards

John B

[johnb]

Found your pics, very impressive. As the Ha is effectively using 1 out of 4 pixels do we take more Ha than RGB.

John B

[Shibby]

Thanks!

Well... It depends...

If the Ha were being registered on all 4 pixels (imagine you have a mono DSLR) then, once scaled down to 1/4 resolution, the image would be less noisy. If you don't scale it down, then the noise levels are comparable (but of course, the resolution is higher). When comparing to DSLR colour, I thiink it's a bit more complicated and depends on the algorithm used to convert the pixel data into an image - usually there is interpolation jiggery-pokery used. I end up processing my images to the resolution of the Ha data. So, sometimes use super-pixel mode on the colour data too.

I personally take a similar number of exposures, but my Ha exposures are longer. The main reason for this is simply that they can be - LP is eliminated, so doesn't wash out the image after 5 minutes. The longer exposures also have a better signal-to-noise ratio.

Anyway, the straight-forward answer I suppose is "yes!"

[pixueto]

How do you combine the different exposures in DSS? I'm thinking about the flat frames for Ha filter and the colour ones.

[Shibby]

How do you combine the different exposures in DSS? I'm thinking about the flat frames for Ha filter and the colour ones.

Sorry for a massively belated reply!

You'll want to stack your Ha frames separately to you colour ones, with their associated calibration frames. Ha can be used to enhance your colour images, but this is via post-processing trickery in (e.g.) Photoshop.

[pixueto]

Thank you