Reprocessed Lagoon and Trifid

[avandonk]

Dug up some old (April) data and reprocessed it. The trouble with getting better at processing is all the previous efforts should be redone.
Details
Canon 5DH, 100ED with AP FR so 640mm at f6.4, 12 x3 min ISO 800, Hutech LPR filter, processed with ImagesPlus, stacked with Registar, digitally developed with IP, gradients removed with GradientXterminator, levels and curves in PS, Richarson Lucy enhancement in IP 7x7 for ten cycles.

You can see the image has some noise and looks a little flat because of the ISO of 800. The dynamic range is not as good as you increase the ISO.That is now why I shoot at an ISO of 200 and for 20 minutes exposure. The trouble with 20 min exposures is that your polar alignment and tracking have to be spot on otherwise you get image rotation. The guide star should also be very close to the centre of the image because even with perfect polar alignment image rotation still occurs if the guide star is off image centre.

1.6MB
http://members.optusnet.com.au/~trlee8/L&T_1.jpg


Bert

[strongmanmike]

Nicely done Bert!

Looks a little red in the surroundings..?..perhaps add some green? Otherwise looks quite nice.

It will be good to see out of season images over the coming weeks as you reprocess actually :thumbsup:

Mike

[RB]

Very nice Bert,

looking forward to see how you go with 200 ISO at 20 min.
Awesome.

:thumbsup:

[avandonk]

You are correct Mike but I think it is something inherent in the 5DH sensitivity to H Alpha. If I increase the green, the green noise in the background sticks out like the proverbial. The Hutech LPR filter does not help as it is missing data in the green and yellow range of wavelengths. So I think what you are seeing is a faithful rendition of what the camera 'saw'. The other complicating factors of course are my eyesight vs world and monitor type and calibration.
I once mentioned to the Chief of the division of CSIRO I used to work for 'colour does not exist, it is merely the ratio of intensities as registered by the three different cones in you eyes and the sensation is interpreted by the brain as colour'. He at first did not believe me. He does now (I think).
Look up Land effect. You can produce colour in an image produced by two or three different black and white positives taken of the same scene through different coloured filters and superimposing the images with slide projectors.
This works even if the filters are both yellow but pass different wavelengths.

Thanks for the advice anyway as none of us has all knowledge anyway, even if we think we do.
What was that about unknown unknowns etc...

Bert

[avandonk]

RB you have already seen the effect of longer exposure at low ISO here
http://members.optusnet.com.au/~cheekyfish/NGC1763.jpg

That is a much dimmer nebula than the Lagoon. Notice no discernible noise in the background and very dim objects are clearer. There are others. One here
http://users.bigpond.net.au/avandonk/LT_s.jpg

Bert

[RB]

:doh: Ah yes, thanks Bert, I'd also like to try shooting at lower ISO once I get my guiding up and running.