Deep? Lagoon and Trifid Widefield

[avandonk]

Inspired by the latest flurry of long a deep images. Thought since focus and tracking etc were all OK would go for a series of long exposures to see how deep I could go. Anything longer than ten minutes on this target under these conditions would saturate the sensor and wash out highlights. I guess short of using masking this is as good as it gets with this setup.
The only real improvement now is the same under dark skies without the LPR filter. This would markedly improve the blue response of the system.

Details
Canon 5DH, Canon 300mm F2.8L at F2.8, Hutech LPR filter, 6X10min at an ISO of 200, in camera noise reduction on. Processed with flats in ImagesPlus stacked with Registar and adjusted levels and curves in PS after digital development in IP. Also a bit of R&L 5x5 for ten cycles.

3.2MB
http://members.optusnet.com.au/~avan...LAG&TRIF_L.jpg

Bert

[iceman (Mike)]

WOW! So sharp across the field. Excellent result, Bert.

The hi-res version is stunning. The trifid looks amazing in the hi-res version.

[h0ughy (David)]

Magnifique! wow some excellent images coming lately, this one is a beauty!

[JohnH]

And that was a single shot! Very nice!

This is a personal observations....is this a mod'd camera? The Milky Way star clouds are normally shown up as brownish/yellow/orange, certainly that is how they look on an image from my 20d (unmoded). Did you alter the white balance or do you think this is a result of the longer exposure and/or the LPR filter?

Also a quick question, why did you choose to shoot at iso 200 with NR on - I am of the understanding it is best to shoot at the highest normal ISO your camera supports (1600 on the 20d) and do darks in s'ware, this maximises your light gathering time, dropping to ISO 800 on a bright object might improve S/N a little but below that there is very marginal, if any, gain to be had.

[avandonk]

Here is a small picture from the same data adjusted to 'normal' camera spectral response. Most stars put out some H alpha radiation (unless they have no Hydrogen) and with a H alpha enhanced camera it obviously shows up in the red channel.
The other consideration is that the Hutech LPR filter knocks out Sodium yellow (as emitted by pesky street lights).
It was actually a stack of six images.
I prefer to use the in camera noise reduction as noise shows up on all exposures no matter what the ISO setting. The noise is inherent in the sensor and is more noticeble at high ISO settings as all the ISO setting does is amplify the collected signal in each site along with any noise present.

The other complication is that we humans can barely see H alpha anyway so if we want to portray it in any nebula it will also show up elsewhere.
Most people are used to widefields produced by colour film which is carefully formulated to have the same spectral sensitivity as the normal human eye.
One exception was Tech Pan B&W film which had good response to H alpha.

If you have any futher questions will do my best to answer them. Maybe I should do a short article on the human visual system and its colour response.
Most people do not realize that the brain does an automatic white balance in real time no matter what the natural lighting conditions and or colour distribution/composition inherent in the scene being viewed.

Bert

[iceman (Mike)]

Originally Posted by bert

Maybe I should do a short article on the human visual system and its colour response.

Yes please! That would be great, and would be a valuable addition to the Articles section.

[JohnH]

Originally Posted by avandonk

...
I prefer to use the in camera noise reduction as noise shows up on all exposures no matter what the ISO setting. The noise is inherent in the sensor and is more noticeble at high ISO settings as all the ISO setting does is amplify the collected signal in each site along with any noise present.

!!!

If this is true then the ISO setting is (almost) irrelevant, so you should set it for the greatest dynamic range and stack to improve s/n ratio? Do you think in camera NR is more effective than darks or is it just a matter of convenience, food for thought there that is for sure...

[Lester]

Hi Bert,

I like the second one. Very nice indeed.

[avandonk]

I have done a careful experiment where I took the same set of exposures of the same object with and without in camera noise reduction on. Also took darks and flats and bias frames. Processed both lots and I think the ICNR won hands down. It is almost impossible to get dark frames that match the exposure unless the camera temperature is exactly the same.
Look here
http://www.iceinspace.com.au/forum/s...ead.php?t=9500

Yes ISO is irrelevant if you use ImagesPlus and careful post processing and the lower the ISO setting the greater the dynamic range. I am next going to try exposing at an ISO of 50.
Also see here
http://www.clarkvision.com/imagedeta...gnal.to.noise/

ISO is taken into account when the camera produces the JPG image or you use any 'normal' software to get Tiffs etc from Raw frames.

Bert

[avandonk]

Maybe I have been looking at the image toooo long. See if the changed large version is better, I prefer the previous or do I ....

bert

[tornado33]

Gee that is deep, Barnard 86 stands out like a sore thumb extreme right side of pic
I must turn your lens onto that area with the Hydrogen Alpha filter in and see how I go.
Scott

[avandonk]

Reprocessed the data to get more detail and tried to get the colour 'right'.

Large image 2.3MB
http://users.bigpond.net.au/avandonk/LT_s.jpg

The uncompressed JPG is 18.6MB!


Bert