Sunday, October 21, 2007

Adventures in lunar photography

Back on August 29th I set up my camera on a tripod and pointed toward the almost-full moon in the eastern sky. Having gotten semi-comfortable with shooting the crescent moon back on the 17th, this became an experiment with taking shots of it with scattered clouds in the sky.

And now, for no discernibly good reason, I now reveal my results (and pretend I know what I'm talking about when it comes to photography even though everything refutes that).

Mostly I was seeing what I'd get by playing around with the lens aperture (how wide the lens opens--the bigger the number the smaller the opening) and with the exposure time (how long the lens is left open while taking the exposure).

All were taken with a 22mm focal length, with (I think) the ISO set at 100. (The ISO isn't stored in the file properties, alas.)

I started with lens aperture at F/7.1, a 1 sec exposure, and got:
Moon is bright (with a spiked corona), but with no surface detail, and the clouds are dim.

Then I opened up the aperture to F/5.6, keeping other settings the same, and got:
Moon is still a bright white circle, but the clouds are a bit more distinct.

Then I further opened the aperture to F/4, still 1 second (and same ISO), and compensated with a +0.7 overexposure, and got:
The moon's corona is smoothed, and the clouds are bit brighter.

And then I reduced the aperture down to F/6.3, no exposure compensation, but extended the exposure to 4 seconds (yes), and got:
And here the moon is really bright (so much so that it's not even a sphere), but on the clouds we can make out shadows.

So I pulled the focal length down to 10mm, knocked the aperture to F/3.2 and pulled the exposure back down to 1 second, and found that bringing in more of the clouds and making the prominence of the indistinct moon less important in the shot, and it didn't seem so bad:
No, it's not that good either...

In the end, what I learned is that getting a brightly lit object and dimly lit objects in the same night sky to show up with decent detail on both is way more difficult than it might seem.

And you've now learned... that I am not above hiding my moments of semi-ineptitude.

1 comment:

  1. Doug:

    You're mixing day with night. The full moon is a daytime exposure: at 100 ISO, start around 1/500 @ f8, then open up from there. Of course, exposure will also be affected by the phase of the moon and sky conditions (haze, clouds).

    One way to get the right amount of detail on both the moon and the clouds is to do two series of exposures, one for the moon, the other for the clouds, and then combine them with Photoshop or a similar program.

    (BTW, this isn't digital "cheating." In the old days of film a photgrapher would combine images but using darkroom analog techinques.)

    Even with Photoshop moon-clouds shots can be tricky when the clouds are passing in front of the moon. Depending upon how thick the clouds are at the moment you take the image, your exposure might be over or under. And the streaking across the moon's face might not match up when you combine the images.

    Hope this helps you out. I just know this stuff after making lots of mistakes shooting the same subject matter.



So, what do you think?