Lovejoy widefield experiment above The Rising Sun

[Kenny]

Great night observing with Mark (and sis), Doug and Rose last night with eyes, bins, dob and DSLR. I took a range of shots of the comet so that I could continue my education in photography and image processing. Target object was Comet Lovejoy. Here are the results.

Canon 450D on standard (non-tracking) mount. Stacked in DSS with 2 flats darks (not enough?), no flats or bias (laziness). Processed in LightZone.

Wide starfield shot of Taurus, Hyades, Pleiades, Perseus and Comet Lovejoy C/2014 Q2. There is a very faint tail showing - there is more tail data showing, however, to display it destroys the rest of the picture. 23 (minus plane trail exposures) / 30 x 13 second exposures (untracked) at 18mm, f/5, ISO-1600.


Cropped version of the above image zero-ing in on the comet.


Two further experiments zoomed in at 88mm with 8 second and 6 second exposures as I was worried about star elongation. Possibly should have worried mvoe about focus!

30 x 8 second exposures at 88mm, f/5.6, ISO-1600.


30 x 6 second exposures at 88mm, f/5.6, ISO-1600.


There doesn't appear to be much difference stripping 2 seconds off the last image.

[The Thing]

Gosh you are a busy bee!.

...
Canon 450D on standard (non-tracking) mount. Stacked in DSS with 2 flats (not enough?), no flats or bias (laziness). Processed in LightZone.
...

Presume by two 'flats' you mean darks! I use 8 as I have been told (I think by MarkS) that that is a statistically good number - or it's just lucky!

[Kenny]

Yes. I meant darks. Is there a target ratio of lights to darks / flats / bias?

[The Thing]

I use 8 darks, 10 flats, 10 bias/offset and as many lights as I can get. There doesn't seem to any benefit I have found out about to having more calibration frames thought I read of people using hundreds.

[MarkS]

Hi Kenny,

You've definitely caught some comet tail there!

However I am finding that the background is very black - I had to take your image and stretch the pixel values by a factor of 4 before I could see either the comet or its tail.  Maybe it is just my screen (but I don't usually have this problem) or maybe you are setting your black point too low.

Mark

[Mike]

Same here Mark. I'm also finding the background super black and finding it hard to see anything. The night sky is not black so don't try to artificially make it black Kenny. It looks unnatural and hides faint data.

[Kenny]

Thanks for the feedback and noted. I have dialed down some of the levels in LightZone because I felt the background sky was too messy / noisy but as you say that is where the faint tail data is. I haven't set a black point before (not sure how) and also not sure how to stretch the pixel values / histogram though I may be partially doing it and not know it by that name. LightZone allows you to relight the picture and also set / stretch zones.

[Kenny]

Ok, finally got around to reprocessing this following my Adobe Photoshop CS2 tutorial on Friday night with Carole. Same data used (30 x 8 sec). My processing skills are still 'amateur' but to me this looks remarkably better than my first attempt.

[The Thing]

Making progress, a huge improvement.

The background diagonal streaking can be got rid of by using one of the sigma staking operations in DSS. Usual settings for me are kappa 1.5 with 1 iteration.