View Full Version here: : M83 (inspired by the image of the week) and M16
28-04-2012, 04:38 PM
Finally - a clear night! Inspired by this week's IIS Image of the Week (Rigel003's great shot of M83: http://www.iceinspace.com.au/forum/showthread.php?t=89811) I thought I'd have another go as well. Have had a few earlier attempts at this object, and this is definitely my best so far.
15x8min with the modded 400D @ ISO800 + darks, flats and dark flats. (cropped)
Also thought i'd have a try at M16. Dialled up 23 x 8min subs, but some high level cloud (or perhaps it was fog) meant that I had to discard 8 subs, leaving the final count at 15 x 8mins as per M83. (this one is also cropped)
Stacked in DSS, and finished in Darktable.
Advice and feedback welcomed.
ps the full frame shots all seem to exhibit some sort of red 'noise' (?) around the edge. not sure if this is just some vignetting effect that im not removing properly with my flats, or if its in-camera. the red around the edge doesn't appear on my darks, and i cant see it in the flats either. Looking back over other astro images from previous sessions it is there as well. Any suggestions?
28-04-2012, 11:42 PM
You have done a good job there Richard with your kit.
Processing is pretty good too, it shows you have a good handle of stretching your data both linearly and non linearly :)
Look forward to your next installment
Nice job Richard with focus and tracking (which I am still working on :rolleyes:). I am very envious, keep them coming! You have inspired me to have a go at these soon too.
29-04-2012, 02:03 PM
I find that focus is easy to achieve with the aid of the Bahtinov mask. I slew to a star nearby the object that I want to shoot. (I'll usually use this as a further alignment point in EQMOD as well). Pop on the mask, and then using a 4 or 5 sec exposure at ISO1600 i can quickly see the diffraction pattern on the laptop screen (im using Backyard EOS). With progressive shots i can then home in on the focus point. I then lock the focus down and slew to the object for imaging. I use a series of 30sec ISO1600 exposures to get the image framing that I want.
Once I've done that I select a guide star with PHD, activate guiding, then do a single exposure at the planned sub time (in this case 8 mins) to check that tracking looks okay. I then dial up the desired sub sequence and i'm away.
In terms of alignment, Im using alignmaster and my procedure there is basically just to run through the alignment process repeatedly until alignmaster tells me I have an alignment error of less than 1 arc minute (ideally less than 30 arc seconds).
Using this procedure I've seen reasonable success so far with subs at 8 mins. (I haven't tried any longer yet, as then next exposure increment in the 400plus firmware hacked intervalometer is 16 minutes, which might be a little long...?)
29-04-2012, 03:10 PM
Well done Richard. A very nice image and heaps better than my last DSLR version. I guess the deep cooling of a dedicated CCD camera just gives you some extra latitude in pushing processing a bit further without too much noise. Nice detail in the galaxy and well represented background field with good star colour. I like the widefield especially. From your description above it sounds like you've got the capture process down pat.
29-04-2012, 04:09 PM
Wow - thanks Graeme :)
Ironing out the kinks in the workflow certainly makes for a more enjoyable and productive imaging session, and i'm obviously pretty happy with the results i've been getting so far. Would love a cooled CCD (i like the look of the ST8300C - maybe next year...), but i know there's still a long way to go until i've exhausted the capability of my current gear.
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