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Heart in Ha

Shibby

By Shibby
in Imaging - Deep Sky

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Shibby

Shibby

Posted
Posted

Over my last three imaging sessions, I've been gathering Ha data on the Heart Nebula (IC 1805) only. My goal was to see if it were possible for me, with enough data, to get a reasonably smooth Ha image with a DSLR.

So, 11 hours of exposure later, I don't think I've quite got there. Maybe this still isn't enough data - or it's possible that I'm being limited by a "noise floor" and longer subexposures are required.

The warm temperatures and/or full moon haven't really helped so I don't think I'm quite ready to call it a day yet on this one!

I have turned the camera in the focuser to achieve what I thought to be a more pleasing framing of the nebula.

66x600s ISO-800

Modded Canon 450D + Baader 7nm Ha filter

Skywatcher 150PDS

Vixen GP

gallery_5051_1080_483843.jpg

I also thought it might be interesting to show the image build up over time, demonstrating the value of stacking lots of data. I applied a (very slapdash) set of curves to the final image at 100% crop. I then applied the exact same curves to a single sub, then continued doubling the number of subs each time.

(NOTE: this animated gif may take a while to download).

gallery_5051_1080_1075975.gif

Thanks for looking :)

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swag72

swag72

Posted
Posted

You have got a good result there Lewis. I read somewhere that when you are imaging with the DSLR and Ha you will always get noise and will not be able to smooth it out. The reason for this is (as I remember it) that data is only collected in the red pixel in the DSLR. So in 3 out of the 4 pixels you actually have no data at all. So, you will never be able to smooth it out as you'll always have areas with no data.

Hopefully someone will confirm this or tell me it's a load of old tosh!! It did make sense though.

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Gina

Gina

Posted
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You have got a good result there Lewis. I read somewhere that when you are imaging with the DSLR and Ha you will always get noise and will not be able to smooth it out. The reason for this is (as I remember it) that data is only collected in the red pixel in the DSLR. So in 3 out of the 4 pixels you actually have no data at all. So, you will never be able to smooth it out as you'll always have areas with no data.

Hopefully someone will confirm this or tell me it's a load of old tosh!! It did make sense though.

I've imaged in Ha with a modded and cooled DSLR and haven't found that. Of course I dump the green and blue channels and their noise with them. Yes, there's only one in four pixels used so the sensitivity is ony a quarter of a mono camera. OTOH the CMOS chip is more sensitive to deep red than other colours which partly makes up for dumping 3 out of 4 pixels. Of course, you don't get this benefit with OIII or SII and exposures will need to be much higher for these filters.
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ollypenrice

ollypenrice

Posted
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Great result and even greater from a DSLR.

The loss of resolution can be attenuated by using a drizzle stack. The dither will be provided by the reframing of so many nights imaging as well as by PA errors etc.

This is not a noisy image though a CCD with 11 hours would certainly go a lot deeper. I think it is quite an achievement myself and very impressive. I 'have my eye in' on this target having just spent some time on it and I think this is a very respectable Ha layer. Nice work.

Olly

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SJJ

SJJ

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Gives hope to all of us dslr users and the animation really illustrates the benefit of spending the time getting all those subs.

It's always very temping to capture a few subs and move on to the next target without having captured enough.

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Shibby

Shibby

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Thanks folks, good to know I'm not wasting my time! :)

Sara, you're right that you can only use 1/4 of the pixels but I don't think this really means there is noise that can't be brought down with enough data. I stack the data in super pixel mode, which just puts all 4 pixels of the bayer matrix into a single pixel, then I just use the red channel so have 1/4 the resolution (1/2 the dimensions).

Olly, I hadn't thought of doing a drizzle stack, so that's very interesting... /strokes chin...

With lots of clear skies (at least forecast to be) on their way and the rotated camera still in the focuser, I'm considering going back yet again for some more data. Not sure, though; I'd probably need to double the integration time again to make a big difference. What do you folks think?

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ollypenrice

ollypenrice

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I think you probably would need to double it, though you might get better S/N at the lower temperatures of later in the year?

In processing you could (if you haven't done so already) apply noise reduction just to the darker parts and then push the contrast just a little harder.

A drizzle routine really does bring down noise...

Olly

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