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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.

Robert Amoruso
09-26-2010, 12:29 PM
Roger,

Same problem I have in Bosque as the earth warms up my 600mm magnifies all the air turbulence and the images are no good. Same thing happens to me in Alaska. Irts cool how you got the moon lined up (and yes I know how to do it) but I hope others note the fact you planned your position in advance.

The overall lack of sharpness in the buildings is something I don't find pleasing however.

Dave Mills
09-26-2010, 01:15 PM
Hi Roger, thanks for the technical info on how the atmospheric conditions can effect an image of this type. Moonrises can take place rather quickly so it's important one plans in advance where to place it as noted.
I agree on the sharpness of the buildings. Would have shot this using a higher fstop(sharpness) but not sure how the decreased SS would of effected the moon. It might of added to the distortion. Interesting image...

Roman Kurywczak
09-27-2010, 01:32 PM
Hey Roger,
Man......you had some atmospheric turbulence!!! I love the concept and comp......but the lack of sharpness kills this one for me. Could you go with Dave's suggestion or would that make it worse?

Roger Clark
09-27-2010, 09:05 PM
Dave, Roman,

The f/stop was not an issue with sharpness, and a longer exposure time would decrease sharpness due to the image moving around. From exposure to exposure parts of the image were moving by numerous pixels, and in different directions in different parts of the image, like looking at something in a swimming pool. I've photographed hundreds, thousands of sun and moon rises and settings, and this was probably some of the worst turbulence I have seen. The buildings are not as bad as presented, as when I downsized, I did not do any sharpening. So I can improve it some. I think I'll start over and perhaps do a linear conversion and try and recover more red in the Moon. But it will have to wait a while--my son is getting married this weekend.
I'll do a repost when I redo it. Of course, there is the other idea--I'll just have to go out again next month and try again.:)

Roger

Roman Kurywczak
09-27-2010, 09:08 PM
Hey Roger,
That's for the explanation! Congrats on your sons wedding too!!!

Dave Mills
09-27-2010, 10:24 PM
Congrats on the wedding Roger....