astrophotography

Last night I found myself on Road 81W about half a mile south of High­way 16. I had my cam­era and my tri­pod, so I thought, Well, why not? Why not take some shots of the Milky Way?

The head­er image, above, is a sin­gle shot of the galaxy above the prairie horizon.

This is a panoram­ic pho­to, nine pho­tos, rough­ly 3×3, to cap­ture more of the height of the galaxy than I could with any sin­gle image.

And this is an 11-image stack of a por­tion of the galaxy, which hope­ful­ly brings out some of the detail bet­ter than any sin­gle shot could.

Info for Nerds

All images were 30 sec­ond expo­sures at 11mm, f/2.8, ISO 3200.

I merged^[1]Use the “Light­en Only” mode, Pat, for future ref­er­ence. 10 dark frames into a sin­gle “dark mas­ter”^[2]Sounds Sith, but it ain’t. to elim­i­nate or at least lim­it hot pix­els in the images. The Image Mag­ick com­mand composite {image}.jpg -compose minus_dst {dark-frame}.jpg {image}_cleaned.jpg is how I did the dark frame subtraction.

The align­ing and stack­ing was done with tools from Hug­in Panora­ma Tools^[3]Hug­in is part of Panora­ma Tools, appar­ent­ly. and Image Mag­ick—align_image_stack *.jpg -a aligned_ to align the images, then mogrify -format jpg *.tif to con­vert the TIFF files to JPEG, most­ly so my com­put­er isn’t bog­ging down try­ing to process huge image files.

The panora­ma was cre­at­ed with Hug­in—my luck with align­ing night-time panora­mas with Hug­inn is hit-or-miss, but I find it gen­er­al­ly can find enough con­trol points in a group of Milky Way shots to do its magic.

…I should just make a page about all that, should­n’t I. A ref­er­ence for my own use, if no one else’s.

Last night I was set­tled in, ready to just watch a bit of TV and then go to bed, when my dar­ling wife texted me:

If the skies are as clear there as they are here, you need to go outside.

So I stepped out onto the patio and yes, yes it was pret­ty clear here. I gath­ered up my cam­eras and tripods and hit the road.

I set up on a grav­el road not too far from town—if I want to, I could prob­a­bly bike there—and snapped a few sets of Milky Way pho­tos. With the 11–16mm lens, I was shoot­ing ten-minute batch­es of 30 sec­ond frames, 11mm, f/2.8, with the ISO chang­ing each ten min­utes: 400, 800, and 1600. I want­ed to see what I could get from the dif­fer­ent ISO settings.

Unfor­tu­nate­ly the dew crept onto my lens—or, more pre­cise­ly, the UV fil­ter I have screwed on over the lens. If I was smart, I’d have removed the fil­ter and re-done my shoot­ing; I think now it was the fil­ter hold­ing in a bit of heat that caused my dew prob­lems.^[1]Appar­ent­ly the sim­ple hack for dew is to wrap a cou­ple hand warm­ers around the lens; you can hold them in place with tape or a beer cozy. Filed away for lat­er exper­i­men­ta­tion.

I man­aged to get two stacks from the ISO 1600 run, and they look pret­ty good, I think. One is 8 images deep, and the oth­er is 10.

I also got a stack of 18 images from the ISO 400 run, and… Well, you can judge for your­self, but I think ISO 1600 is the sweet spot between “detail” and “noise” (at least for me). Maybe ISO 800 would work, if I can keep the lens from mist­ing over…

There was quite the auro­ra show last night, and I’m going through my pho­tos from that, but first I decid­ed to process the 24 shots I took of the Milky Way. Two hours’ pro­cess­ing gets you the above photo.

The Process

I took some notes as I processed the images, because I want to do more of this and get bet­ter at it. The image, as eye-catch­ing as it is, is pret­ty noisy, and I’m pret­ty sure there are bet­ter ways to do some of the things I did. But, for the nerd crowd (I know you’re out there, I can hear you breath­ing), here’s how I made this par­tic­u­lar image:

• snapped 24^[1]One frame was wonky, so the final stack is 23 images deep. pho­tos (aka “light frames”), 15 sec­onds, 24mm, f/2.8, ISO 3200
• snapped 3 dark frames, ie, left the set­tings the same and put the lens cap on
• did dark frame sub­trac­tion on every frame (opened each light frame and a dark frame in Gnu IMP as lay­ers, dark frame on top, and set the Lay­er Mode to “Sub­tract”)^[2]This gets rid of the cam­er­a’s “hot pixels”—the first time I tried stack­ing the images, I got smeary blue and red lines from the hot pix­els.
• align images with align_image_stack -a aligned_ *.JPG ^[3]Part of Hug­in.
• con­vert aligned images to JPG using mogrify -format jpg *.tif^[4]part of Image Mag­ick. (most­ly so I don’t over­load my poor laptop)
• open aligned images as lay­ers in Gnu IMP
• set each lay­er mode as “Dodge”
• export­ed the whole she­bang as a JPG
• re-opened the export­ed JPG
• Used Gnu IMP’s Fil­ter → Enhance → Noise Reduc­tion and cranked that baby up to 11 ^[5]16, actu­al­ly.
• prof­it

Things to try next time:

• shoot RAW
• try a low­er ISO value

It was clear last night, so off I went to Rid­ing Moun­tain to get some Milky Way pho­tos. I shot a cou­ple of panora­mas, one just off the high­way on the golf course / Wish­ing Well turnoff, the oth­er at Spruces (thanks again, Tim!).

As I was leav­ing, thin clouds had start­ed to roll in, and the moon—still half-full—was ris­ing in the east.