Help needed please with filters, processing and an OSC camera

[LaurenceT]

Novice imager here,  I have an asi533MC pro camera and I've used it with my Askar FMA180 scope in the past using an Optolong L-Enhance filter. The images it produced had some blue fringing and I was advised that the colour correction is less than optimal and to use an Astronomik L3 luminance filter to correct this. Last night was my first opportunity and I got one hour of NGC7000 in before the clouds, 60x60 second lights, no calibration frames (yet).

The ASIair produced AsiFitsView files, a text document and a JPG file for each sub. When I look at the JPG file in Windows Photo viewer I can see mild red colour in the nebula. I stacked the AsiFitsView files in both DSS (which I've just started learning yesterday) and AsiStudio DeepStack and to my amazement it produced a greyscale image! I'm now assuming that's exactly what a luminance filter does. So my question is how do I finally get a colour image. Do I make another set of subs with my L-Enhance filter? If I do how do I do this in the same imaging session and can I then process both the luminance images and narrowband images together?

[Paul Puntin]

Hi Laurence, in DSS you need to ensure you tell it you have fits files generated by a colour camera. See the screenshot here http://deepskystacker.free.fr/english/index.html otherwise you will get a grayscale image. You access this dialogue box from the options list on the bottom left of the screen. Click “Raw/Fits DPP settings” and click the fits files tab. Make sure the camera setting is rggb.

A luminance filter is effectively just a clear filter that blocks light outside of the visible spectrum (UV and IR). 
 

ASI stacker probably has a similar setting somewhere.

[Elp]

The luminence filter doesn't result in a greyscale image, it's simply a UV/IR block filter and passes everything in between so you get a starfield devoid of star bloat which happens due to IR. You don't tend to notice the bloat on the target.

Your software should have a debayer option, that is what generates the colour image from the camera, most software defaults to an RGGB pixel matrix which the majority of camera sensors use in their construction. If you've used DSS it should output a colour image by default if you've fed it colour data.

I don't think you can process both the Lenhance and L3 data together as they're both colour and they'd mix together if you tried. They'd have to be done separately then in GIMP or PS you use the Lenhance data as the default RGB and then use the L3 as a top layer and set the blend mode to luminence, or you can process the Lenhance data starless and use the stars from the L3 layer.

[LaurenceT]

I finally managed to get something out of it, can't say I'm particularly impressed with it!

[knobby]

You'd need to get more time on it to improve things, nothing wrong with that image, with only 1 hour of data it's going to be fairly noisy.

[LaurenceT]

2 minutes ago, knobby said:

You'd need to get more time on it to improve things, nothing wrong with that image, with only 1 hour of data it's going to be fairly noisy.

It's the massive number of stars that bothers me but you're quite correct about the amount of data.

[knobby]

Ah, if you don't like the stars you could try Starnet, it's free ! worth a bash !

[LaurenceT]

57 minutes ago, knobby said:

Ah, if you don't like the stars you could try Starnet, it's free ! worth a bash !

I did download it but couldn't open the zip file!

Extracted it now.

Edited November 6, 2023 by LaurenceT

[LaurenceT]

Another session last night, same gear but with L-Enhance filter instead, 200x60s subs, no calibration frames.

[LaurenceT]

Same image with stars removed and background extraction done, just for fun!

[knobby]

Looking good.

[The Lazy Astronomer]

23 hours ago, LaurenceT said:

 can't say I'm particularly impressed with it!

Important thing to note: the L3 is a broadband filter; it allows all wavelengths of light between approx 420 - 680 nm to pass through. The l-enhance is a dual narrowband filter (albeit a fairly we wide one) - it blocks around 80 - 90% of wavelengths and allows a small section around 500nm (Oiii & Hb emissions), and 656 nm (Ha emission). 

The L-enhance, as all narrowband filters, greatly improves contrast on emission nebulae by virtue of blocking most of the rest of the light spectrum.

[LaurenceT]

20 hours ago, The Lazy Astronomer said:

Important thing to note: the L3 is a broadband filter; it allows all wavelengths of light between approx 420 - 680 nm to pass through. The l-enhance is a dual narrowband filter (albeit a fairly we wide one) - it blocks around 80 - 90% of wavelengths and allows a small section around 500nm (Oiii & Hb emissions), and 656 nm (Ha emission). 

The L-enhance, as all narrowband filters, greatly improves contrast on emission nebulae by virtue of blocking most of the rest of the light spectrum.

Thanks for that, I'm now trying to learn how to process dual narrowband images from an OSC camera in Astro Pixel Processor and not PixInsight. I've found a suitable video so I'll proceed with that.