Have a look at this small crop of a telephoto picture:
Doesn't look very pretty, does it? I can assure you, this is not a lens problem, this is not front or back focusing. It's the air. Have a look at another crop from the same shot:
You can clearly see the distortion at the uprights in the barriers. This is called scintillation and it is due to rapid small-scale changes in air density between the camera and the subject. This is simply hot air going up. The picture was taken from about 500 m on a hot day.
I started noticing this effect when I tried to test my new Sigma 150-600 at infinity. I put it on a tripod and focused on a distant target. Then, I noticed that the image in the viewfinder (or even more in live view, when you zoom in) is twinkling and shimmering. Any picture taken in such conditions, regardless of the shutter speed, would be blurred, as above.
I wonder how much air scintillation affects typical wildlife photography. I guess it doesn't matter that much at shorter distances, let's say 50 m. There is not enough air between the camera and the animal to make a significant distortion. But at longer distances on a hot day? It might contribute a lot to a softness of the resulting image. So, some of the telephoto pictures we take can be limited not by the lens or sensor, but... by the weather.
Doesn't look very pretty, does it? I can assure you, this is not a lens problem, this is not front or back focusing. It's the air. Have a look at another crop from the same shot:
You can clearly see the distortion at the uprights in the barriers. This is called scintillation and it is due to rapid small-scale changes in air density between the camera and the subject. This is simply hot air going up. The picture was taken from about 500 m on a hot day.
I started noticing this effect when I tried to test my new Sigma 150-600 at infinity. I put it on a tripod and focused on a distant target. Then, I noticed that the image in the viewfinder (or even more in live view, when you zoom in) is twinkling and shimmering. Any picture taken in such conditions, regardless of the shutter speed, would be blurred, as above.
I wonder how much air scintillation affects typical wildlife photography. I guess it doesn't matter that much at shorter distances, let's say 50 m. There is not enough air between the camera and the animal to make a significant distortion. But at longer distances on a hot day? It might contribute a lot to a softness of the resulting image. So, some of the telephoto pictures we take can be limited not by the lens or sensor, but... by the weather.
