Focus Area: Where Should the Camera Look to Focus?

When you're using auto focus, which is most of the time, you've (perhaps unknowingly) ALREADY instructed the camera where to search for its focus point.  And it will find the most prominent thing in that searched area.  Suppose there was a bird ten feet behind the bird feeder so that you can see both the bird feeder and the bird.  If your focus area is set to Wide (or equivalent term on your camera), the camera will search the wide area for its focus .... and the bird feeder will be in focus and the bird will be less in focus. 

If you had used a much smaller focus area (once again term vary but look for a smaller focus box), then you could position the small focus box on the bird.  The bird will then be in focus and the bird feeder will be less in focus.

Generally speaking, it's easiest to use a Wide focus area if that focuses on the thing you want. If it doesn't then you need to make your focus area progressively smaller until you're able to focus on the thing that you want.  The more complicated the scene, the most precise (i.e. smaller) the focus area needs to be.

This is something that you need to consider in every birding shot.  So you need to know how to quickly and easily change the focus area.  (Pro tip:  If it's buried inside menu section 2.12.8 then it's not easy to find).  Consider setting one of your camera's program buttons to focus area or setting your Function ("fn") button to include focus area.

Metering Mode

The metering mode is functionally a little similar to the focus area.  If you've requested the camera to calculate any of the three exposure triangle settings (aperture, shutter, ISO) then the metering mode comes into play.  This means that if you're in aperture Mode, Shutter Priority mode or using Auto ISO, then this applies.  In other words, it only does NOT apply if you're in full Manual mode and you've explicitly set the aperture, shutter and ISO (not using AutoISO).

A quick little deviation.  Every colour is comprised of a red,green and blue (aka RGB) component.  And these numbers range from 0(darkest) to 255(brightest).  For example, black is RGB(0,0,0), white is RGB(255,255,255) and the Home Depot orange is RGB(249,99,2).  Your camera is happiest with an image that has the brightness of blah middle grey.  Middle grey is achieved when each of the RGB channels (Red,Green,Blue) are halfway between their darkest (black) and brightest (white).  Anything brighter than middle grey is considered too bright and similarly anything darker than middle grey is considered too dark. So your camera will calculate the overall brightness of your photo and attempt to bring it closer to middle grey.  Back to metering mode.... 

If the camera is calculating any of the three exposure settings, then you must instruct it where to look to determine the initial brightness of the image.  This is known as the "metering mode" or "metering area".  Different cameras use different terms for their metering modes.  My Sony has metering areas of Multi, Center, Spot (Large), Spot (Standard), Entire Screen Average, and Highlight.

Suppose you have your metering mode to the full screen (your camera may call it "screen average").  Then every part of the frame is used to calculate the overall brightness of the image. And the camera make its calculation based on that.  If you're taking a picture of a bright empty sky, this is a very bright image.  Let's call it 100 out of 100 on a fictitious brightness scale.  Your camera will consider this to be a very bright image and will darken it in an attempt to bring it closer to middle grey.

If a bird appears in the sky, then the overall brightness of that image is less than 100 but probably still something like 99.5 because the dark bird is relatively very small compared to the big sky.  If you take the picture, the camera will once again darken the entire image.  This may result in an overly blue sky and, probably worse, a way-too-dark bird.

If you had changed your metering mode to be a much smaller area, then you could have placed the small metering area on the bird (yeah, this sounds like the focusing area discussion above).  Your camera would only consider the portion of the image inside the metering area.  If the bird filled the metering area, the camera would think this is a dark image and would calculate its settings to brighten the picture.  This would result in a maybe too-bright sky and a better exposed bird.

Alternatively, you could have kept the screen average mode and used Exposure Compensation to bump up the exposure.  The camera would've done its calculation based on middle grey and then increased its calculated value to make the image brighter than it would normally be.

Exercise:

1. Put your camera on a tripod.  You'll want identical compositions for each of these photos. 

2. Compose any scene.

3. Go into automatic mode and take any picture A.

4. Go into manual mode and manually set aperture, shutter, ISO to the same settings just calculated by the automatic mode. Take picture B.  Pictures A and B should be identical.

5. Change metering mode to screen average. Change ISO to auto ISO.  Take picture C.  Pictures A, B, C should be identical.

6. Change metering mode to spot.

7. Without changing the composition, move the metering area to a bright spot.  Take picture D.  See what ISO the camera calculated.

8. Without changing the composition, move the metering area to a dark spot. Take picture E.  See what ISO the camera calculated. Pictures D and E will likely have different ISO values.

All images are the same (which is why you're on a tripod).  If screen average metering mode was used for images D and E, the calculated ISOs should be the same.  However, since spot metering was used, the camera and the spot used had different brightness levels, so the camera probably calculated different ISOs.