Saturday, October 24, 2009

Jail House

While I was out behind the Mission last weekend, I found that one of the stone ruins back there was this old jail house with no roof. It seemed like the perfect subject for a shot of the night sky.

18mm, 2 minutes at f/4.0 and ISO 800

There was some wind earlier this week that blew away all of the haze in Santa Barbara, so I jumped at the opportunity to try out this shot on a clear night.

A recent gift from my wife came in handy on this outing; she got me one of those huge 4 D-battery Maglites. It made it a little less terrifying tramping along the trail in the dark, and was really helpful for lighting up the jail house so that I could focus the lens on it.

The funny thing was, once I had crossed through the park, I realized the jail house was on the complete opposite side, and there was a road literally right behind it! Oh well, though; walking through the dark made it more exciting :)

To set this shot up, I mounted the camera on the tripod at its lowest setting, maybe 8 inches off the ground, and used the cable release. I had planned to get more of the building in the shot, but there was a big bush there blocking me from backing up anymore. The trees in the background also constrained the angle that I could shoot at if I wanted the sky in the picture, so this seemed like pretty much the only way to frame it.

It took 5 test exposures to get it right. At these shutter speeds, I was out there for a good 30 minutes just to get those 5 shots. For the final shot, I opened the lens wide at f/4.0, then set the shutter speed to 'bulb' and timed the exposure manually with a sports watch for 2 minutes.

I had done one earlier exposure at 4 minutes, but found that at that length the stars movement is pretty noticeable. "Star trails" are a pretty cool effect, but if you go that direction I think you kind of want to go all the way, so I stuck with 2 minutes and bumped the ISO instead.

I probably spent a couple hours playing with this photo to get the look right. I discovered that an important problem with taking photos of a starry sky is the camera's white balance. If you're not sure what white balance is, there's a superb article on the subject here. The problem was that the light on the building came from the headlights of passing cars, and the headlights have a much different color temperature than the light of the stars.

Camera auto-WB, 4450K

Because of the complexities here with the colors, it was tempting to just go with a monotone treatment and make this a black & white or maybe sepia image. The contrast between the cool sky and warm light on the stone was just too good to pass up, though.

There were two different approaches I could think of to resolving this white balance problem. One would be to bring the image into Photoshop, divide the building and sky into two layers, and adjust their white balance separately.

Another approach, which I decided to go with instead, was to use the Adjustment Brush in Lightroom to select just the sky.

Selecting the sky using the adjustment brush

I desaturated the sky (not completely, though) and applied a light blue color (I have to thank Jess again for helping choose just the right color of blue for this). This had the added benefit of cleaning up what I think must have been noise in the stars--the stars were all slightly different colors in the original.

I read an interesting tutorial on creating really dramatic star trails, here. I hope I get a chance to try it out!

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