M51, longish exposure

[ollypenrice]

This is the result of 4.5 hrs lum and an hour of binned colour per channel. How do people get that really extended halo?? Phew.

The first half of the lum was in 5 min subs, the second in 6 min. I'd go for the latter or longer.

I always lack colour saturation on galaxies, I feel. Any idea why?

I combine In AA and blend in the lum in PS. I'm at the noise limit on saturation here.

Meade 127 apo and Atik 16HR.

Fantastic weather at the moment, here. Sorry about that!!

Olly.

[beamish]

Nice close-up Olly. Very nice indeed.

Karlo

[blinky]

I think you are being a little harsh on yourself, thats as good an M51 as I have seen!

[brendant]

Stunning image Olly, fantastic detail even in the background galaxies, one of the best images I have seen

Excellent imaging and processing, well done.

Brendan

[adamsp123]

My goodness, a wonderful image!

[ashenlight]

That is amazing olly. I've never done any imaging myself so I don't really know the ins and outs of producing an image as fantastic as that, but well done. Love the background detail, as Brendan said. Beautiful

[mcrossley]

Really nice image Olly, I think the colour saturation is fine, certainly don't think it needs any more.

If I was being really picky I'd shift the cyan tones more towards the blue, which to my eye would give a more natural look.

4.5 hours though - dedication! - I've not had 4.5 minutes in the last month

[Petervde]

Great image, Olly !

Peter

[Doc]

So you have pinched all the good weather Olly.

Cracking M51 that.

[MikeD]

Very nice result Olly, lovey smooooth image.

Well worth the time spent on it.:icon_cheers:

Mike.

[Vega]

I think those 4.5 hours of clear sky were meant to be shared between the rest of us Olly. . lol

Brilliant image mate. The dedication has really paid off.

Matt

[Sam]

Great image Olly, that's one of the best M51's I've seen for a while. How about flicking some of those clear skies over here?

Sam

[Beyond_Vision]

A fantastic capture Olly time well spent

Regards

Kevin

[Psychobilly]

Very nice Olley

Almost "Robesque"

Billy...

[RobH]

Cor Olly, that's gorgeous!

Can't wait to get home now and add some more data to mine ;-)

Cheers

Rob

[Tim]

Great image Olly, really sweet. Just for the hell of it I might combine yours and Robs in registar and see what pops out

So this was 7.5 hours in total?

[ollypenrice]

Great image Olly, really sweet. Just for the hell of it I might combine yours and Robs in registar and see what pops out

So this was 7.5 hours in total?

Yup. 1 hr per channel colour, binned and two lum runs. The first was 2 hours in 5 min subs and the second 2.5 ish in 6 min subs. I increased the time because there was no core burning issue, the guiding was great and I wanted to get the halo.

I would be deeply honoured to share a screen with The Master!

Olly.

[RobH]

You've embarrassed me Olly!!!!

Go for it Tim....hey Olly, when I've got a few more subs for mine, I could stick them on a cd and send them to you, you could do the same with yours and we could both have a play with the data if you fancy it?...they are both with a 16HR so would fit well together.

Cheers

Rob

[ZOG]

That is lovely Olly. M51 is one of my favourites and your image is up there with the best.

[ngc2403]

lovely image, really good sharp focus! colour seems good perhaps a minor change like the ones already mentioned.

halo problems ... hmm how do you take ur flats?

if you are not careful then you maybe making the SNR of the halo worse by not using enough high quality flat fields. Flats can make the SNR of faint objects worse at times.

i notice that the galaxy seems to stop sharply? i assume that you have cleverly used curves to slower the signal of the noisier parts hence leaving the galaxy standing out from the background with a good SNR and hiding the noisier halo area.

To check that your flats are of the correct quality, try taking more (~100 images) brighter flats (>40000 Intensity) and applying them to your image to see what happens.

other than that i don't now how you don't have the halo, it's faint but with that data you should have it all be it not with at best SNR, but still it should be there and am sure you want the best out of those long hours spent imaging.

Ally

[narrowbandpaul]

I cannot over emphasise the importance of a good flatfield.

The quality of a flat field is Sff*Nff...where Sff= signal in the flat field, Nff= number of flat fields averaged.

A good flat field allows the sensor to operate in the shot noise regime for the entire dynamic range.

Shot noise is the most important regime for attaining high SNR. In this regime, the SNR increases as sqrt(exp time)....which is the best you can do.

Typically you will need about 20 flats at about 3/4 full well (about 40,000DN)

Secondly, it appears as if you may have clipped the black end of the histogram. If the black point is too high, then low signal stuff gets mapped to black, and the info is lost.

Try not touching the black point at all, or at least very little.

The image is very good though, and 4.5 hours ought to show what you are after.

Hope this helps, good luck

Paul

[ollypenrice]

Ally, thanks for your input. I'm not saying I don't have the halo - it shows better, indeed very well I'd say, on the high res version. And no, the way it stops suddenly is the way it is in on the hardly-processed images. It seems to stop like that on some of the best I've looked at (Russell Croman, Karel Teuwen and other luminaries.)

Flats? Ah, confession time - no flats and no darks, though with the 285 darks have no perceptible effect. I've tried them.

Rob, great idea. Let's try it. I'll PM you.

Olly.

[Tim]

Olly, Rob, if you dont have Registar, then I can combine both sets of stacked FITs for you and send them to you both for processing if you like.

Olly, you never use flats??????

And Paul, I'm a little confused on those figures. I usually do my flats at around 20000ADU, or about 1/3 full well. 40000 would be closer to 2/3 than 3/4 wouldn't it? (Can you tell numbers make my brain ache?) Is that definetly 'right' ?

[RobH]

Cheers Tim.

I'm happy to wait until I have more subs, then get all my subs and Ollys and stack them to get the full value of the better S/N ratio that will produce.

Olly, I too am surprised you don't take flats...your gear must be really clean, I've never seen a dust ***** on any of your images!

Tim, I, and almost everyone else I've ever heard of, does their flats at about 1/3 of full well depth....mine are done at between 28 and 30.000 adu and work perfectly. I do 20 of them for each filter to keep the S/N down nice and low.

Cheers

Rob

[RobH]

Strange....the filter for rude words just removed B-U-N-N-Y .....well, 50 years old and I thought I knew all the rude words there were....obviously wrong!!!