Foggy Focus

Mozziephotography

Mozziephotography

Suspended / Banned
Messages
1,850
Name
Stephen
Edit My Images
Yes
Spent well over an hour in the wind, mist and rain on the top of Holme Moss photographing runners in a fell race. Had to change the spot I'd chosen to "snap" due to the fact that the rain would hit the lens head on. Moved near to a nice boggy bit with plenty of water, hoping to capture a few splashes. Chose a 50mm prime for my D7200 and awaited the first runners. The camera found it difficult to focus through the mist and the first lot of images were more like Manet/|Monet paintings. Things did improve when the mist became less dense. What is happening to the camera's focusing ability when it's foggy?
 
There are two focusing systems. With contrast based systems, in fog there is not enough contrast for the camera to detect maximum contrast. With phase based systems, the multiple lenses (aka water droplets) are providing too many phase differences for the system to know which ones to go by.
 
Couldn't use manual focus because of the speed of the runners and the different routes they took across the bog. When I've edited the images, the bottom half of the runner isn't too bad but any part of the body with sky behind them, looks darker. I'll just have to be satisfied with the outcome. It's a learning curve.
 
mossienet said:
Couldn't use manual focus because of the speed of the runners and the different routes they took across the bog. When I've edited the images, the bottom half of the runner isn't too bad but any part of the body with sky behind them, looks darker. I'll just have to be satisfied with the outcome. It's a learning curve.
Click to expand...

Of course you could have used manual focus. How do you think sports photographers managed in the days of film before auto focus. The trick is to pre focus on a spot the runners are going to be at and then take the picture.
 
You obviously have taken part in a fell run. (Smiley face thingy) They DON'T run on a track, they choose their own route to avoid water, rocks, etc etc. I know what you mean but it just wouldn't happen. So many changes of direction.
 
There just wasn't enough contrast/detail for the AF system. The same thing can happen in low light, or when trying to focus on something with a lack of detail/contrast like a blank wall...

john.margetts said:
With phase based systems, the multiple lenses (aka water droplets) are providing too many phase differences for the system to know which ones to go by.
Click to expand...
I highly doubt that.
The phase based system is still dependent on image contrast; it compares multiple separate images, taken from separate parts of the objective lens, for position (phase) on the sensors. The less distinct the images are, the worse it is going to perform.
 
mossienet said:
Couldn't use manual focus because of the speed of the runners and the different routes they took across the bog. When I've edited the images, the bottom half of the runner isn't too bad but any part of the body with sky behind them, looks darker. I'll just have to be satisfied with the outcome. It's a learning curve.
Click to expand...
You could give yourself a bit more depth of field to play with by raising the ISO above 250 (rather low for the conditions), which will let you stop down the aperture a bit while maintaining the same shutter speed. But it also looks like there may be more mist at head height - in some shots the leg is quite clear, but further up the body is 'hazy' even when it seems to be the same distance from the camera.
 
They look fine to me, nice and atmospheric. I agree with @Retune about upping the ISO and and stopping down a bit, a bit of noise in those conditions isn't really going to detract from the photo.
 
I was really surprised with the low ISO. I shoot in manual because the runners speed varies as you work through the field. Set the speed to 1/800th and aperture to f5.6 I thought that the ISO would be 1600 or so. Does the fog/mist have some effect on the readings?
 
Fog disperses a lot of light towards the lens (and every other direction) rather than letting it be adsorbed by the scene so there is a lot of light going in the lens.
 
You must log in or register to reply here.
Back
Top