There is a wealth of information on metering modes available online but almost none of this info makes specific reference to scenarios that us as wildlife photographers face in the field. Whether its on our digital photography course or the wildlife photography course that I host, or even on safari, the question on the various metering modes always pops up.
I’m going to try and make the various metering modes simple to understand using a couple of “out of the box’ illustrations which I hope will resonate with some of you.
The Technical Stuff
Every camera has a sensor which, when exposed to light, creates an image. The camera also has a secondary sensor which measures the light that’s coming through the lens and determines how much is needed to produce a well-exposed photo based on the scene in front of you. As light is reflected from a scene or subject through the lens, it hits the mirror in front of the imaging sensor and is reflected up to the camera’s focusing screen and metering sensor and the camera assigns a shutter speed (in Auto, P and AV) modes.
The majority of cameras these days will have Spot, Partial, Centre-weighted Average and Evaluative (Matrix) metering modes, all of which work in the same way. Each of these modes takes readings from different parts of a scene in order to calculate the shutter speed necessary for obtaining a “correctly exposed” image. As the name suggests, Spot metering offers the most precise metering – anywhere from 1.5%-10% of the total picture area, depending on the camera – while at the other end of the scale, evaluative metering takes a series of readings in zones that covers around 80% of the entire frame.
This “Cheat Sheet” from Digital Camera World pretty much sums up how and where these various metering modes are taking light values from when selected.
Now, lets see how this works in the field.
Assume we are shooting in evaluative metering mode and we have selected the right hand focus points to achieve focus on our very bright white egret to the right of frame. The camera will now measure light across pretty much the entire frame with a bias towards the active focus point.
Now, this is where I’m going to share how my mind works to try and illustrate what happens when the camera meters of the scene and gives you a shutter speed based on your desired aperture value and ISO setting.
Please keep in mind that these are not actual values but I’m using this to illustrate the way evaluative metering mode works – bare with me on this one!
In order to correctly expose the darker areas of a scene the camera would need to use a slower shutter speed (1/125) in order to allow sufficient light in and correctly expose these shadows or darker areas. At the same time the camera is picking up average shutter speeds for the mid tone areas (1/250 – 1/320) and then a very fast shutter speed (1/1000) for the bright egret which takes up only a small portion of the frame.
Based on all of this information the camera then averages out the shutter speeds to keep the exposure “in the middle” and not too dark (underexposed) or too bright (overexposed). In this instance the camera may have chosen an average shutter speed of 1/320 to capture this scene. As you can see, the egret ends up being overexposed but we can see some detail in the shadows.
In spot metering mode where the camera will use ONLY the centre focus point to meter the scene the results are dramatically different.
Placing the centre focus point over your subject (only the new intermediate to professional level camera bodies has spot metering linked to the active AF point) and then locking the exposure (using the * or AE Lock button), you can now recompose and place your subject back on the desired focus points with the exposure reading locked to the original position of the centre AF point. Based on this, the camera would have used only 2-4% of the frame to gain a reading and assign a shutter speed linked to the exposure value.
This means that the camera ignores the dark backgrounds and exposes only for the subject.
Thats an example of a bright subject on a dark background, now lets look at the converse.
Here is an Open-billed Stork is set against a bright background and, in evaluative metering mode, the camera once again measures light across pretty much the entire frame with a bias towards the active focus point.
Using my hypothetical analogy of assigning shutter speeds across the scene where the camera is metering from, the camera may have decided on something along the following lines.
Clearly the scene is dominated by faster shutter speeds (1/1250) assigned by the camera to ensure that the bright water does not end up being over exposed. Unfortunately for us, the dark subject which occupies only a small portion of the frame has only two shutter speeds of 1/125 assigned to it. In the bigger picture (pun intended) the bright water wins the battle and the camera would have chosen a shutter speed of 1/1250 which is too fast a shutter speed to render our subject correctly exposed.
Changing into spot metering mode and, once again, using our central focus point to meter before using the * or AE -Lock button to lock the exposure, the camera is only metering off of the dark subject resulting in a slower shutter speed (1/125) which ensures that our subject is correctly exposed.
If you’ve grasped this concept you will see how each of these metering modes have their merits and quirks. The tricky bit with spot metering is the fact that you will not only need to change modes but will also need to lock your exposure on your subject if you are using anything other than your central focus point (unless you have set this up in the menu system on a newer intermediate to professional level camera body).
You will also, as always, need to be acutely aware of your shutter speeds to ensure that you eliminate any chance of camera shake or movement within the frame (unless you are panning of course)
When to use these Metering Modes in Wildlife Photography
Evaluative metering does a pretty good job 90% of the time and its really only in difficult lighting that one may need to consider switching into spot metering mode.
In the way that I analyse a scene and capture an image, I am constantly aware of the light within the scene and will more often than not, make some sort of manual exposure compensation adjustment which uses the cameras initial evaluation of the scene (based on evaluative metering mode) as a starting point before being adjusted to either underexpose (darken, faster shutter speed) or overexpose (brighten, slower shutter speed) a scene.
If you are wandering whether you cant achieve the same results as spot metering by using exposure compensation in evaluative metering mode then you are on the right track. This will be the subject of my next post which will look at “Manual Exposure Compensation in Wildlife Photography”.
Spot Metering in wildlife photography for me is almost only used in very harsh lighting situations or when shooting at night with the aid of a correctly positioned spotlight. Here the camera ignores the entire scene except for the centre focus point where the concentration of light is at its brightest. Rather than taking the super slow shutter speeds needed to correctly expose the pitch black areas where no light is falling, the camera just looks at the centre point and the light that is falling on that small 2-4% of the frame.
This results in faster shutter speeds and, you guessed it, sharper images.
I hope this helps shed some light on how the various metering modes work and how they can be used to deal with different lighting situations.
The really exciting part comes when you understand how to use manual exposure compensation to override the cameras evaluation of the scene and ensure that your RAW image is as close to your intended interpretation as possible.
Thats what I’ll be sharing in my follow up post so please feel free to leave a comment if you have any questions or comments on what I’ve covered here.
Share this Post