Monday 26 January 2009

Techniques - Metering

One of the comments we had early on was for some technique tips on metering, or more correctly shooting mode.

For most of my work these days, I tend to use M Mode. All the images on the Short Eared Owl post were taken in M mode, and I will tell you how I did it a little further on. When I started off my wildlife photography, it was either Av or Tv mode, depending on the speed of the subject. Control of the depth of field is probably the most overarching variable to control. We often prefer to just isolate our subject, blur out the background so all concentration is on the subject and we are not distracted by busy and cluttered backgrounds. However, this is something that we should be looking closely at when taking the image. Often with Birds in flight, I wait before I press the shutter button so the subject is in the right part of the scene, rather than just snap away.

However, there are other times, such as with the Armilleria fungus in this post, I actually wanted to get a good sense of the environment of the forest to put the subject in place.

Anyway, before I get too distracted by depth of field, lets concentrate on shooting mode With Av mode, we control the aperture, setting the depth field at whatever subject distance and focal length we are using. The camera then sets the required shutter speeds, based on whatever ISO and metering pattern you have selected. We will cover the metering mode (spot, matrix, partial etc) and the different options at a later date, as this is worthy of a separate posting.

Now Av is fine as long as your subject is in a reasonably consistent background. So what if your subject, lets say a Red Kite is one minute against a bright sky and the next against the dark tones of trees . If you are in one of the auto or semi auto modes, your exposure is going to be all over the place. Yet, the light may not have changed on the subject, and that is what we want the exposure for. In Av mode, we might have been at + 1 1/2 stops to counter the bright sky, which is going to be clearly very wrong for when the subject dips below the tree line.

To counter this, I shoot in M mode - but how do I set the three variables f ISO, aperture and shutter speed. Simple - meter from a suitable mid tone, grass is a good place to start. For the Owls, I metered from the foreground grass, took a shot, checked the histogram and that was that. Using the ISO to ensure that the shutter speeds was in the right sort of range, the aperture set for the depth of field I wanted, and the shutter speed fast enough to make sure I had a fighting chance of a sharp image.

Once the exposure set, then I can forget it and just get shooting, and wherever the bird goes, it will be correctly exposed won't it? Well not quite - you do have to keep an eye on the light levels. So when the sun is popping in and out of the clouds, you do need to adjust the exposure to ensure a consistent exposure. But you will be surprised how sensitive you get to the changes in light, and it will become instinctive you to dial in the extra light you need.

So there you go, if you haven't tried it, give it a go, let us know how you get on


1 comment:

  1. That looks like a familiar 'lecture'..... ;-)
    All good stuff. One point I'd make though is that you don't need to meter from a mid-tone. As long as you can determine whether something is brighter or darker than a mid-tone, and by how much, you can meter from any tone.