A 'third way' approach to mono vs OSC imaging options

[tomato]

Having received some positive replies to the notion of imaging mono NB with a dual band filter and combining this with dual band filter OSC data, and see other imager's results using this approach, I have had my first go at this.

This is 57x 3 mins with the Esprit150/QHY268mono/NBZ combination and 52x3mins with the Esprit150/QHY268OSC/NBZ, so 5.45 hrs integration in total.

Contrast this with this image 155x3 mins of Esprit150/IMX571OSC/NBZ, 7.75 hrs integration:

I know, this is far and away from being a direct comparison, the OSC only data was captured under a 95% full moon for a start, the Lum/OSC combination was captured under much better conditions. However, I think it demonstrates that using a dual band NB filter with a mono camera to create a combined NB 'Luminance' channel does have some advantages over the dual band OSC only approach.

[Elp]

Obvs difference but how will the mono dual band filter data distinguish between ha and o3? Depending on the target it may be better to use singular ha and o3 filters to use as luminence boosting data, I do it with ha mostly.

[gorann]

Interesting Steve! A comparison you could make that could be convincing is to compare your mono data with a grayscale version of your osc data, using the same number of subs from the same times at night. I assume you used the dual rig so already have that data from the same night. Will the data from the mono camera show significantly more detail and depth?

Edited January 16, 2023 by gorann

[ollypenrice]

What you're trying, here, seems to me to be analgous with LRGB imaging in the sense that the mono camera catches more signal but does not distinguish between gases/colours. You are relying on the Bayer Matrix of the OSC camera to make that distinction. The question is, how much of this distinction do you need and will this system provide enough of it? Your result strikes me as promising, since it bears a strong resemblance to the colours and colour separation I obtained using Ha 0III LRGB. (I remember being very surprised by the colour of the OIII outer shell but yours is similar.) A related question would be,  Does the extra signal of the mono camera over the OSC  compensate for its inability to add to the colour differentiation? 

I'd also be thinking that, in what is close to a natural colour image, natural star colour would be nice.

Olly

[tomato]

Thanks for the feedback.

The idea is that the depth and detail is captured in the Lum channel, leaving the dual band OSC detail to differentiate and obtain the colour. I combined the channels using LRGB combination in Pixinsight.

Of course, it is never going to be as good as mono and individual NB filters, but that is not the point. However, can it be better than just dual band filter OSC data,  as it is just as easy and convenient to capture, especially on a dual rig.

@gorann, I’ll put the greyscale comparison together, perhaps you could try it on your dual RASA rig, assuming you have a suitable mono camera?

[tomato]

OK,  so here are stacks of the best 30 subs of Mono and OSC NBZ data, taken on the dual rig so the sky conditions were the same. No gradient removal or processing, StarXterminator used then an STF stretch applied in PI and saved as Jpeg images.

Mono

OSC

The mono is exhibiting more detail to my eye and is less noisey. I'll do a few more before deciding if this will be my default set up on the dual rig, and thereby releases a OSC camera for the RASA if I can muster the energy to set up and take down again...😉

[gorann]

Interesting and convincing Steve! It clearly looks like the mono is capturing more detail. But then as @ollypenrice points out you may loose out on colour infomation, so maybe it depends on the target. Using the mono-OSC approach could be superior on bright objects like the jellyfish, but if you hunt for weak Oiii from a SNR, maybe two OSC would be better as you want to separate out as much Oiii as possible. Just speculating.

But I am tempted to put my QHY268MM with NBZ on one of my RASAs. In cases where I know that I am looking for weak Oiii maybe I would use a Oiii filter on the mono camera, and add it to the blue channel. Fun with experiments but not so fun to remove the camera from a RASA as you never know what the stars will look like next time

Edited January 17, 2023 by gorann

[ollypenrice]

8 hours ago, gorann said:

Interesting and convincing Steve! It clearly looks like the mono is capturing more detail. But then as @ollypenrice points out you may loose out on colour infomation, so maybe it depends on the target. Using the mono-OSC approach could be superior on bright objects like the jellyfish, but if you hunt for weak Oiii from a SNR, maybe two OSC would be better as you want to separate out as much Oiii as possible. Just speculating.

But I am tempted to put my QHY268MM with NBZ on one of my RASAs. In cases where I know that I am looking for weak Oiii maybe I would use a Oiii filter on the mono camera, and add it to the blue channel. Fun with experiments but not so fun to remove the camera from a RASA as you never know what the stars will look like next time

Agreed on all counts - including not taking the camera off the RASA!!

Olly

[tomato]

Yes, taking cameras off and putting them on a F7 refractor is a lot less fraught, I do it a lot!