Can high-tension lines degrade image quality?
I've been trying to photograph foxes, there den is under many high-tension lines (about 2/3 mile upstream from a 35,600 kW power generating dam). I'm using a Canon 400mm F2.8 L USM lens on Canon EOS 5D III and 7D II bodies. I'm sitting for five or six hours each session, directly under the wires.
The images are soft - it looks like I'm shooting through heat shimmer. It isn't that I'm missing the focus - there are no sharp points anywhere in the image. I've shot a few hundred thousand shots with this gear on this tripod. I miss the focus now and then, but the set up has been proven repeatedly, so we're not dealing with motion blur. I'm in a blind only ~35 feet from the den, hard to believe there's enough heat shimmer to distort an image. The same gear works well once I'm away from the high-tension lines.
Is there something that could be interfering? I wondered if the magnetic field from the lines might be strong enough to be corrupting the card. But, I'd expect that to give file read/write errors rather than affect the image. (The affect is the same writing to both SD and CF cards).
Anyone have any thoughts?