Hello! Long time lurker first time poster. I’ve been into photography since the very late 1990s/early 2000s and been using Darktable full time since 2014. Mostly on Linux but also on Mac OS X, although the latter is seeing less and less use. Trying to interact with the community more, I’m bad at that …
At any rate among my other hats I’m an astronomer and would like to share a couple of photos I processed in Darktable over the last few months. First one is the total lunar eclipse form back in January. Nothing terribly special here, it’s was pretty clean straight out of camera. Just a little adjustment for the highlights on the limb of the moon, levels adjustment to bring up the shadows, equalizer for the details/color and profiled denoise (was at ISO 2000). Shot with a Nikon D7500 and 200-500mm f/5.6. The poor Nikon’s buttons quit working due to the cold (-3°F at the time) but it came back to life after a warm up.
Second photo is of Comet 46/P Wirtanen back in December, also edited in Darktable. This shot took quite a bit more processing. I do like the equalizer module for astrophotos, I used it here to bring up the luma and chroma on the more coarse details to help beat the noise down. Other than that I used profile denoise, some levels adjustments, increased saturation, used the tone curve to bring out contrast along with defringe and lens corrections to help get the chromatic aberrations under control. Shot with a Fuji X-T2 and 35mm prime at f/2.8 and ISO 3200.
Yeah, Astrobin does that too and I think Xephem or Cartes Du Ciel will do similar things. Although it looks a little off, it’s missed Aldebaran and Alcyone by a few arcseconds. Looks like Taurus in its entirety is shifted slightly east, Perseus looks spot on though. Thanks!
Some sites say your lens does exhibit edge distortions but it’s simply correctable in software. I’m wondering if it is that rather than the overlay (which should not be in error…). Do you have any other Taurus imagery? The fact that it’s bad in one corner to me suggests an element in the lens has been slightly knocked out of its holder, which happened to me with my nifty fifty. Any ideas?
I’d like to try the two Unix programs you mentioned but I’m overseas and away from my computing resources.
Nice photos!
Could you elaborate more on the shooting and pre-processing (if there was any)?
To clarify: have you taken multiple shots and then registered and stacked them? With which software?
It’s also a crop from the 35mm frame (maybe 75% IIRC) so that’s not quite on the edge. I didn’t apply distortion correction in Darktable, however the lens correction module says “camera/lens combination not found” on the RAF when I cut it on. Just a Fuji X-T2 and 35mm f/1.4 R. Do I need to submit some RAW samples? I know they take them for the white balance/RAW support on new cameras but I’m not sure how the lens correction data is built TBH.
If the lens is out of whack it’s not by much. It’s only a few months old, performs wonderfully and hasn’t seen any hard knocks or rough duty yet. Don’t have access to an optical bench anymore though. Probably should take it apart just yet as it still has a warranty.
Sure, the lunar eclipse was pretty straight forward since I was under 1" of exposure. Just at 500mm on the lens with the D7500. I was using a cheap intervalometer to get regular shots throughout the night. Unfortunately the stiff wind ruined a number of them. No dark, bias or flat frames. Just straight processed in Darktable with the highlights/shadows, tone curve, levels, contrast lightness saturation and equalizer modules. Used the equalizer to bring up the middle-coarseness luminance for details enhancement. Increased saturation, brought the shadows up for more openness in the reddish area and the highlights down for the limb area. Used the two pass noise reduction approach in profiled denoise (both set to wavelets, one set to HSV color and the other to HSV luminance blend modes).
The capture on the comet shot was done with a Sky-Watcher tracking mount as I was going for 60" expsoures. I picked that up with the X-T2 as I usually use a GEM mount but that’s big and cumbersome and I wanted something easier to haul out. This was the first real test of it, I think it did OK. More or less same procedure for editing but with more equalizer modules and more saturation. I don’t really do stacking of darks/bias/flats on something this simple. Heck I don’t really do it unless I’m reducing data these days as modern sensors are very good at noise control.
I didn’t, both were single exposures. In the past for making what I call pretty pictures I’ve used Deep Sky Stacker in a VM. I think it will run in Wine these days but I haven’t tried it in a while.
Don’t you see a lot of hot pixels with the XT-2 during long exposures? Mine shows a number of hot pixels even at very moderately “long” exposures such as 8".
Haven’t noticed any on mine out of the ordinary no. My D800 is bad about that but the few on the X-T2 are easily picked up with the hot pixel Darktable module. Again this is just for pretty picture making, taking data I wouldn’t advise that.
Probably should take it apart just yet as it still has a warranty.