12 Mar 2008

Aperture Value

Carl posted a comment yesterday about Ken Terry's beautiful wildlife pictures.

Ken said that he used ISO 1000 and an aperture of f5.0 in AV mode as the light was changing so quickly. Sometimes the shutter speed was 1/500 and sometimes 1/4000.

Carl commented:
...really enjoyed this. But trying to work out what AV is, in relation to rapidly changing light?

'AV' - Aperture Value - is an automatic exposure mode in which you set the aperture you want and the camera decides on the correct shutter speed to match it. This can be very useful in rapidly changing light conditions like those Ken experienced when he was photographing the red kites and the red squirrels. In these conditions it can be difficult, if not impossible, to constantly adjust the exposure manually. In other words, you just cannot keep up with the fast changing light levels by correcting the exposure yourself in the Manual ('M') mode. When shooting a fast-moving subject like a bird in flight, operating the camera quickly is vitally important, so setting the exposure mode to an automatic setting can be a boon and one less thing to bother about.

So in Ken's case, he set f5.0 in 'AV' mode. When the sun went behind cloud and the light level dropped, the camera chose a shutter speed 1/500sec. When the sun came out and light level went up, the camera chose a shutter speed of 1/4000sec.

Some time ago I posted a photograph of Freddie Mercury. Click the link below. I used 'AV' exposure mode for this because the stage lights in the studio where the photograph was taken were constantly going on and off, with light levels going up and down. It would have been impossible to keep up with the exposure manually in 'M' mode, so I set something like f2.8 in 'AV' mode and let the camera sort out the shutter speed.

Just one tip here... Aperture Value (AV) used to me known as Aperture Priority (AP), far more sensible and descriptive. Until some fool decided to change it.

1 comment:

Carl said...

Many thanks Philip - I didn't realise that someone had changed it! I saw the 'f' value wasn't changing much, so assumed that the camera was on aperture priority and the shutter speed was being used to 'chase' the exposure. That makes perfect sense - I will just have to add yet another term to my list!!