Ngc4939

[lhansen (Lars)]

This is a sequence of images taken over the last 2 nights. It is quite a difficult subject and the colour noise is obvious.

L 48 * 5min unbinned
RGB 16 * 5min each unbinned

RCOS 12.5, PME, ST8XME

Seeing was average with FWHM of around 1.8-2.2

[TrevorW]

I'd be happy with FWHM of 1.8-2.2 average.

Personally I'd be aiming for longer subs at least 10 minutes and with your set up probably more. All in all Lars a very fine set of images to keep. if any

Improvement I'd look to some enhancement in processing to remove background noise, improve colour and definition in the dust lanes

[gregbradley]

Interesting galaxy. I don't think I have seen that one before. Very nice.

I don't see a lot of noise. You mean a bit of colour noise in the spiral arms? Blur tool can reduce that, it needs a bit of smoothing in the arms whereas the core could take a bit of sharpening.

With regards to exposure length there is a CCD calc by Wodaski.
My understanding is read noise of the camera will largely determine your ability to choose exposure lengths. In your case though, with a blooming chip, you are limited by blooms which I have never had to deal with but I believe they can be hard to handle.

Your read noise may mean multiple 5 minute images will have more noise in it than half as many 10 minute images. The SBIG camera is pretty noisy by todays standards in that regard. But on the other hand blooms will make your life hard too. So perhaps 5 minutes is the compromise.

Galaxy looks a bit grey, whereas it probably is more bluish with a more yellowish core.

Seeing of 1.8-2.2 is pretty good as far as I can tell from my experience.

Overall a very good image and nice round stars.

Greg.

[bluescope]

What a beautiful galaxy ... well done Lars ... the spiral arms looks great ... must have a look at this myself one night.

[gregbradley]

Here's a possible repro Lars with just the 47kb thumbnail image:

http://www.pbase.com/image/124543978

Greg.

[Peter Ward]

Originally Posted by gregbradley

... The SBIG camera is pretty noisy by todays standards in that regard. ....

??!! Kodak's noise spec on that sensor is 15e-

SBIG's implementation is also 15e-

[lhansen (Lars)]

I like the colours and brightness better but it seems to have been at the loss of some definition.

What can you do with this one?

[h0ughy (David)]

like what you have done in the first shot - its like an artists pallete - the interpretaion and enjoyment is different for everyone

[lhansen (Lars)]

I have kicked off tonights imaging run for this DSO. All 10 minute subs, RGB binned 2* total of 6 hours

It will be interesting to see the outcome tomorrow morning


Stay tuned

[gregbradley]

Originally Posted by lhansen

I like the colours and brightness better but it seems to have been at the loss of some definition.

Yes that's true. The only solution to the colour noise in the arms
I know of is smoothing and that is the price.
Greg.

What can you do with this one?

Can you email me a larger file of this?

A beautiful shot. Noise control is the main issue. Its a hard small dim target so getting enough signal is the battle.

Greg.

[lhansen (Lars)]

Hi Greg

PM me your email address and I'll try. Do you want separate luminance and colour stacks?

Cheers

Lars

Originally Posted by gregbradley

Can you email me a larger file of this?

A beautiful shot. Noise control is the main issue. Its a hard small dim target so getting enough signal is the battle.

Greg.

[lhansen (Lars)]

As promised, this is the image from last nights session. Unfortunately I was only able to get 30 mins each RGB binned 2* because the DSO was below the level of my observatory wall.

FWHM values of around 2.2 for the L and 3.2 for the RGB channels. Not a great night and the processing has been rough and ready

So this is the combination of:
L 18*10mins Unbinned
RGB 3*10 mins each binned 2*

setup and processing as per previous image

[gregbradley]

Better signal and less noise. Did you add in the other nights exposures as well?

Greg.

[multiweb (Marc)]

Beautiful galaxy - very smooth processing.

[lhansen (Lars)]

Hi Greg

No, that is just last nights data. The colour channels are noisy as all heck as you would expect with only 3 images per channel. Luminance fared a bit better.

I normally do a RGBLBGR step case image sequence but due to the low elevation of the DSO after the L channel, I missed out on the last set of RGB exposures.

Unfortunately the weather is not going to let me get another night in for at least a few days

Lars

Originally Posted by gregbradley

Better signal and less noise. Did you add in the other nights exposures as well?

Greg.

[lhansen (Lars)]

Thanks Marc, I really need to spend a LOT more time processing this image.

Originally Posted by multiweb

Beautiful galaxy - very smooth processing.

[mill (Martin)]

That looks really good and with more exposures it will be a ripper