Friday, December 10, 2010

Early evening sun, snow and mist

click photo to enlarge
It's surprising how much of the detail of what you learn in school stays with you throughout your life. I was looking at a cup of cold tea the other day and into my head popped the phrase "colloidal substance". A colloid, as I recall, is a substance dispersed evenly throughout another substance. The word was explained to me by my teacher by reference to, among other things, cold tea. The following day I was looking for a late afternoon/early evening photograph while walking along a track past the village of Bicker when mist started to roll in from the north west. As I started to take my photographs of the trees and church tower with the bright disc of the sun above, the mist started to thicken and the whole of the horizon gradually disappeared from view, the landscape becoming enveloped in a thick fog.

On my journey home I tried to remember the precise difference between mist and fog as it had been explained to me in geography lessons. I recollected that the density of water droplets and the consequent degree of visibility was what separated one from the other, and it was in the hundreds of yards (metres today I suppose), but I couldn't recall the precise figure. So, later that day I looked it up. The current definition of fog is visibility less than 200 metres. However, if you are a pilot it is less than 1000 metres. That latter fact wasn't one I knew and puzzles me somewhat. Do pilots have enhanced vision? As far as mist goes, it is the discernible presence of water droplets with visibility greater than 200 metres.

So, by my reckoning this photograph, which incidentally was taken from near the point where I took this one the other day, shows mist. What it doesn't show is how cold that afternoon was. The temperature was about -8 Celsius (not cold in world terms, but quite nippy as far as the UK goes), however the perceived temperature was a good bit lower due to the wind. The time I had my gloves off to change lenses was as long as I could stand it, and I haven't felt that cold for a few decades - in fact, the last occasion would probably be when I was at school learning about colloids, and the difference between mist and fog!

photograph and text (c) T. Boughen

Camera: Canon
Mode: Aperture Priority
Focal Length: 228mm
F No: f8
Shutter Speed: 1/200
ISO: 100
Exposure Compensation: 0 EV
Image Stabilisation: On