M42 and Rosette Nebula 12/12/09

[Daniel]

Hi All, Haven't been on the forum for quite a while now, been hectic at work, and haven't had time to image even when there was good weather.

Anyway, I'm just about to start work so I won't be able to go into all the imaging details yet, but will post them later tonight.

Anyway, here they are, I didn't have time to take the seperate core subs for M42, will have to add these later.

Daniel
:O)

[MarkS]

Both are excellent images Daniel. 
They really look as if they've been done from a dark site .

I'm looking forward to seeing the imaging details.

Mark

[Carole]

Great imaging again Daniel.
Looking forward to details.

Carole

[MarkS]

Daniel,

I've just been comparing your Rosette to mine http://forum.orpington-astronomy.org.uk/index.php?topic=5482.0 from a darkish site and your M42 to Chris's http://forum.orpington-astronomy.org.uk/index.php?topic=5449 from a very dark site.

I reckon your Rosette is better than mine and your M42 is almost as good as Chris's.  It certainly gives a very interesting comparison for your Hyperstar setup with CLS filter from a light polluted environment.

So I'm very interested to know your exposure details etc.  It certainly shows the benefit of a very fast F-ratio.

Mark

[Daniel]

Thanks guy's, the relatively short subs at low iso definitely help keep noise low. though I was trying for ages to get my stars as nicely coloured as Marks, and failed!

Imaging details are :-



Imaging Scope = C14 with Hyperstar III
Camera = Canon 40D (Modded)
Ambient Temperature = 3 Degrees Celcius
Filters Used = CLS
Date Taken = 12/12/09    
Light Frames = 34x180s ISO 160(Rosette)   25x150s ISO 160(M42)
Dark Frames = 20x180s ISO 160(Rosette)   No darks Applied (M42)
Flat frames = 100x1/13s ISO 160
Bias  = 100x1/8000s ISO

Funny thing Is im starting to wonder what Darks actually do because I stacked the rosette image with and without darks and couldn't tell the difference even after stretching.

Daniel

[Carole]

the relatively short subs at low iso definitely help keep noise low

Funny thing Is im starting to wonder what Darks actually do because I stacked the rosette image with and without darks and couldn't tell the difference even after stretching.

Could these two be connected?  
I found the same with my recent image of M42 which I stacked with and without darks (because DSS was playing up), in fact the one without darks looked to have less noise to me than the one with darks.  

Carole

[Daniel]

Hi Carole, Normally, I'd use ISO 800 for imaging as this has a good balance in signal to noise. But with the hyperstar I'd be at my maximum amount of exposure after only 30 seconds at ISO 800.

The only way I can expose for longer and collect more photons is to use a lower ISO, this also has 2 main advantages as firstly ISO 160 has less noise than ISO 800, even with longer exposures, and secondly, it has higher dynamic range so the seperations between tones is greater and stars don't white out so easily.

I picked ISO 160 over 100 or 200 as the research i've done suggests that this has the optimal signal to noise ratio for the 40D

Daniel
:O)

[Daniel]

Oh, by the way, here's an RRGB composite which I actually used the luminance channel of to get the final colour image above.

[MarkS]

Daniel,

Thanks for the image details, they are very helpful.

Your Rosette has half the integration time of mine but looks better (though your star colours are caused by the CLS filter which I didn't use).  Your M42 has a slightly longer total integration time than Chris's.  I'll go away and do some maths on this to see if your stunning results are in line with theory.

With your camera, short subs and 3C ambient temperature then darks won't make any real difference because there is very little accumulation of electrons caused by dark current.  What darks do is to remove any fixed patterning due to dark current i.e. the background pattern caused by some pixels being "hot pixels" i.e. those pixels that have higher dark current than their neighbours.  If you animate a sequence of darks you will notice that although each dark is fairly random, some pixels are consistently brighter than others - because they have a higher dark current - it is this effect that is removed from your image by applying darks.

A very nice couple of image - well done.

Mark

[Fay]

Fantastic Daniel, took my breath away   (now on oxygen)

[Mac]

very nice.

You must have a machine tucked away in woolwich which removes clouds.
Send it up here when you've finished i could do with a cloud free night.

Mac.

[RobertM]

Wow Daniel,  You never fail to impress, the M42 image in particular has a marvelous 3d feel to it.  They would both be absolutely awesome from a dark site.  The really faint nebulosity in the Rosette image is a but grainy so it might be an idea to combine it with much longer subs and then use an HDR type merge (in PS or using something like easyHDR).  Just a thought...

Also nice pointy stars right out to the edge - very impressive optics (and collimation).

Robert

[Daniel]

Thanks guy's, what I wouldn't give to lug this lot to a dark site, well, you never know, I might just get my act together for the next DSC.

Unfortunately, as far as taking longer subs, 180s at ISO 160 reallly is my limit from my area, I'd love to go longer, but the light polution is too much otherwise.

Just out of interest, when looking at a sub'ss histogram, how far to the right hand side should the spike be before it's too over saturated, I tend to stop my exposures once they get about half way across.

Daniel
:O)

[RobertM]

If it's > 30,000 (assuming a 16bit 64k range) I usually give up and go in for a beer instead.  With that location and the kit you have I think you have to go with what works for you.

[Fay]

Daniel, what capture program do you use for your Canon?