The meters in digital cameras are incredibly sophisticated and growing more advanced each year. So why use a handheld meter? There are two very good reasons:
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1)They encourage you to work in a different way, leading to a better understanding of light and contrast and the way it’s affecting your subject. You’re no longer locked into that little rectangle in the viewfinder.
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2)They let you take ‘incident’ light readings, which reproduce your subjects in their proper tones, whether they are light or dark. The meters in cameras simply can’t do this without human intervention.
This is a Gossen Digisix. It has a diffuser which slides over the light sensor for taking ‘incident light’ readings. Here, though, it’s been moved to the right to expose the sensor for regular ‘reflected light’ readings. This is where you point the meter at the scene as see how much light is being reflected back from your subject. This is how all camera meters work.
We’re all used to automatic cameras where all you have to do is press the shutter release. Handheld meters are much more ‘manual’ and you have to pay attention to the settings. First, you must make sure that the meter’s ISO is set to the ISO you’re going to be shooting at with the camera.
To take a reading, point the meter at the subject and press the metering button (the ‘M’ button on the Digisix). One click ‘locks’ the reading, so you can then look at the display to read it off. The illustrations shows how a typical handheld meter ‘reads’ a scene. The angle of view is generally around 30 degrees, sometimes more, and it’s illustrated here by the red masking around the picture edges which show that the meter’s only reading from the central area. The point about handheld meters is that you can take readings from different areas - the foreground and the sky, for example - and then average them to arrive at an exposure which will capture both. It’s a subject for another tutorial, perhaps.
Let’s say this is the meter reading we got from the scene above. The value is ’14EV’ followed by a single dot. 14EV is the brightness value the meter has measured and the single dot indicates that it’s actually a third of a stop (or EV value) higher. It’s up to you how accurate you want to be.
This exposure value must now be transferred to the meter’s main dial. This is the white, outer dial on the Digisix. It must be rotated so that the value in the clear window under the red index marker is the same as the one displayed on the LCD.
Now you read off all the possible shutter speed and aperture combinations for this exposure using the outer ring. This is the beauty of manual metering - it makes you choose, and hence think about what you’re doing. Here, for example, we might go for an exposure of 1/250sec at f9. If we wanted more depth of field we might choose 1/60 at f18 or, if we were using a long telephoto with the risk of camera shake, 1/500sec at f6.3.
Now that we know the aperture and shutter speed we need, we can set this on the camera by first switching to manual mode (left) and then applying the settings (right).
Now for a different situtation, where the value of an incident light meter really becomes obvious. We’ve got a dark subject against a dark background, and the shot on the left is what the meter in our digital SLR produced, choosing an exposure of 6sec at f11. It’s far too light, and the reason for this is that the camera can’t possibly identify what it’s looking at and whether it ought to look light or dark. All it can do is adjust the exposure so that it’s reproduced as a mid-grey tone (18% grey, strictly) in the hope that’s about right. The picture on the right is correct, properly reproducing the black lens against the black backround with an exposure of 1.6sec at f11. This was achieved using an incident light reading, where the meter measures the light falling on the subject, not the light reflected from it. The camera’s meter was overexposing by around 2 stops (EV) because of the subject’s unusually dark tone.
This is how it’s done. First, the meter’s diffuser is slid over the sensor...
Now the reading is taken with the meter held next to the subject and pointed towards the camera.
As long as the lighting doesn’t change, this same incident reading can be used for any other subject. This little white sake cup was shot against a white background and the camera’s meter has produced a predictably ‘grey’ image, left, with an exposure of 0.5sec at f11. The incident reading we obtained for the shot of the lens, though, works just as well here, reproducing the white tones properly with an exposure of 1.6sec at f11. Because of the subject’s very light tones, the camera was underexposing by around 1.5 stops (EV).
The light meters built into cameras are undeniably useful. There are many occasions when there’s simply no time to mess around with manual light measurements. However, the increasing sophistication of these built-in metering systems won’t overcome the inescapable, inherent limitations of reflected light readings. Perhaps the makers think that if they blind us with science we might not notice.
Copyright © Rod Lawton 2008
