Light meters...once and for all
Posted: Sat Aug 18, 2007 2:08 pmLet’s sort out some misconceptions about light meters….the in-camera type and the separate hand-held type. I’m gonna stick my neck out here and I know I’ll cop some flack from some of our more experienced photographers…..but here it is anyway. The hand-held (incident type) light meters are NOT more accurate than the light meter in your modern digital SLR. They simply require less thought. Here’s how they differ…the light meter in your camera measures reflected light and will give you a deadly accurate exposure providing it is pointed at something that represents an average daylight scene. So what is an average daylight scene? It is a scene that contains a mixture of blacks, whites and greys that if mixed together in a bucket will give you essentially the same tone as a Kodak 18% grey card. How often does that happen you might ask? Surprisingly, most of the time. The meter in your camera will always presume the camera is metering off a scene that reflects 18% of the light. The problems arise when your scene contains an excess of black or white, then the meter will indicate an inaccurate exposure. Picture a camera on a tripod set to Auto mode. A light shines from behind the camera and the subject is an 18% grey card. The cameras meter will give an accurate exposure value. Let’s pluck a value and say F8 at 1/60. Now replace the card with a black card and what does the camera assume? It assumes the same card is there but someone turned the light levels down. For a black card the meter will now give a reading of around F4 to compensate for what it thinks is a lower light level. Place a white card into the scene and the camera still thinks it looking at the grey card but now assumes that the light levels have been increased….so it now indicates around f16. Note…the correct exposure for the black and white card is the same as for the grey card…f8. Now, what does all this mean for the photographer?...simple, if your scene contains average tones then trust your meter, If your scene contains predominantly dark tones then CLOSE DOWN the iris 1 or 2 stops…if predominantly white tones then OPEN UP the iris 1 or 2 stops. (Note that these are not the instinctive actions one would presume to be correct). After a short while of evaluating tones in relation to the grey card you will become surprisingly skilled and your exposures will be exactly the same as if you used a hand-held meter.
Now, let’s look at the hand held meter. Go back to our camera on the tripod measuring the value of a grey card.. Instead of pointing the meter at the card, we point it at the light source. It will measure F8…same as the cameras meter. But, when we change the grey card for a black or white card the setting still reads F8 because we haven’t altered the brightness of the light. The incident light meter reads the light before it bounces off the subject so it’s not influenced by the tones or the reflectivity of the subject. However, it is still not a perfect light meter and has to be used with some discretion. Both types of meter can’t automatically adjust for back lighting and the photographer has to make an adjustment for that. Also, the incident type meter can be fooled by strong side lighting…so once again the photographer has to use his experience. Another handicap of the incident meter is that you need to use an extra hand to employ it and you need to make sure that the ISO is set to the ISO set on the camera. At around $700 for a decent meter it is also a big investment so is it worth it? Well, for a wedding photographer or someone who shoots a lot of products….probably yes. For a street or sports photographer….no. Regardless of what type of meter you use it still has to be used with intelligence and experience and some evaluation of the scene needs to be taken into account. Basically, if you understand your built-in meter then you have everything you need. Your built-in meter also has one advantage over most incident meters….it reads over a matrix….can sense colours, and has a huge at hand database to assist in fine tuning the exposure. Hope this helps clear things up a little.
Now, let’s look at the hand held meter. Go back to our camera on the tripod measuring the value of a grey card.. Instead of pointing the meter at the card, we point it at the light source. It will measure F8…same as the cameras meter. But, when we change the grey card for a black or white card the setting still reads F8 because we haven’t altered the brightness of the light. The incident light meter reads the light before it bounces off the subject so it’s not influenced by the tones or the reflectivity of the subject. However, it is still not a perfect light meter and has to be used with some discretion. Both types of meter can’t automatically adjust for back lighting and the photographer has to make an adjustment for that. Also, the incident type meter can be fooled by strong side lighting…so once again the photographer has to use his experience. Another handicap of the incident meter is that you need to use an extra hand to employ it and you need to make sure that the ISO is set to the ISO set on the camera. At around $700 for a decent meter it is also a big investment so is it worth it? Well, for a wedding photographer or someone who shoots a lot of products….probably yes. For a street or sports photographer….no. Regardless of what type of meter you use it still has to be used with intelligence and experience and some evaluation of the scene needs to be taken into account. Basically, if you understand your built-in meter then you have everything you need. Your built-in meter also has one advantage over most incident meters….it reads over a matrix….can sense colours, and has a huge at hand database to assist in fine tuning the exposure. Hope this helps clear things up a little.
