Roger Clark
09-26-2010, 09:40 AM
I am not happy with this image. I computed the azimuth and time of moonrise and positioned myself to get the Moon rising behind Denver. There were two issues: 1) atmospheric absorption and turbulence. With the distance to the horizon about 30 miles, the atmospheric path was huge. Even though it appeared to be a beautiful clear day, this image shows it actually was not that clear. The absorption in the atmosphere was very high, and if you put the image in a photo editor, you will see that there is zero hint of the Moon in the blue channel and the red channel is saturated. The atmosphere was bery turbulent with the lights jumping by several pixels from exposure to exposure, and blur induced within a single exposure. The distortion at the bottom of the Moon shows an extreme effect of atmospheric refraction. The top edge of the moon has a green fringe, also due to refraction. Actually, that is the green flash effect we sometimes see with the sun. So this is the green flash with the Moon. The atmospheric absorption resulted in a long, 0.8 second, exposure time.
So with the red channel saturated and nothing in the blue channel, all the detail in the Moon comes from the green channel. After this image, I experimented with shorter exposure times to not saturate the red channel, but the exposure times had to be so short, that not much of the city shows. So I like this image best from the sequence (plus the position of the moon).
What do you think?
Canon 1D Mark IV, 500 mm f/4 L IS telephoto lens (IS off) + 1.4x TC giving 700 mm at f/5.6. Exposure was 0.8 second at f/5.6, ISO 200. Mirror lockup on a tripod. Crop to 9 megapixels.
So with the red channel saturated and nothing in the blue channel, all the detail in the Moon comes from the green channel. After this image, I experimented with shorter exposure times to not saturate the red channel, but the exposure times had to be so short, that not much of the city shows. So I like this image best from the sequence (plus the position of the moon).
What do you think?
Canon 1D Mark IV, 500 mm f/4 L IS telephoto lens (IS off) + 1.4x TC giving 700 mm at f/5.6. Exposure was 0.8 second at f/5.6, ISO 200. Mirror lockup on a tripod. Crop to 9 megapixels.