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How to use an ambient light meter

Franz Pritz , Jan 04, 2000; 02:41 p.m.

I mostly shoot landscapes, often in available light conditions. As I recognized that my built in AE meter wasn't accurate enough for defining the correct exposure I bought a Gossen Sixtomat light meter to improve my work. The little booklet coming with the light meter encouraged me to use the ambient light meter because it was more accurate metering difficult light situations but it didn't deliver any rules when and when not to use it. As I surfed the archives I found some postings which said that one had to adopt the meter readings when metering dark or bright surfaces - but the other way round as with reflective readings. As far as I understand, ambient light meters meter the light and no surfaces!? Are there any other hints important for ambient light reading, musts or donts? Any adcvice would be highly appreciated. Franz

Responses

Phil Stiles , Jan 04, 2000; 02:58 p.m.

Ambient light is non-directional. Incident light meters typically have a white dome, and measure the light falling on a subject. (Generally most accurate, because the reading isn't dependent on the reflectance of the subject.) In-camera meters, and the usual hand held meters, read reflected light from the subject. If it's a cat in a coal bin, they will give you an overexposed negative. If the subject is a polar bear on an ice flow in sunshine, they will give you an underexposed negative. Perhaps your manual is separating "ambient" light from electronic flash, which is another metering mode. And let's not forget there may be several different exposures which are "correct," depending on how you visualize the final result. For a generally accurate incident reading, hold the meter at the subject, and aim it toward the camera. Don't hold the meter in your own shadow. You will be measuring both the ambient light, and any directional light which happens to be falling on your subject.

Tom Johnston , Jan 04, 2000; 03:30 p.m.

Incident readings are generally very accurate. However, in knowledgable hands, reflected readings taken with a spot meter are the most accurate of all.

Even incident readings, however, often require interpretation. For example, if you use an incident meter to read the light falling on a very dark subject, you should give a little more exposure than the meter recommends. On the other hand, with a very light subject, you should reduce exposure slightly from what the meter recommends. This is not because the meter is inaccurate, it is because of the nature of the film and it's ability to record detail at certain exposure levels. It has to do with film latitude. In most situations, however, you can rely on an incident meter to give you excellent results. Of course, this assumes that you have tested your films and know what E.I. to rate them at. Incident meters do not allow you to measure subject brightness ranges like reflected (including spot) meters do. The ability to do this is especially important to b&w photographers and is fundamental to the use of the Zone System.

Too often the term incident is confused with ambient. Ambient light, as the poster above pointed out, is simply the existing non-directional light in any scene. You're sitting in ambient light as you read this especially if I have added any illumination to this subject at all.

Jeffrey Rodgers , Jan 04, 2000; 04:07 p.m.

I would like to add one note on extremely low light levels: unless you have a very sensitive meter, you're better off going by instinct and also bracketing. Part of my reasoning is film reciprocation(did I spell that right?)

Jeff Polaski , Jan 05, 2000; 07:24 a.m.

All of the above is useful. Having used all sorts of meters over the years, I didn't really start to understand exposure until I read about the Zone System. Whether or not you use the Zone System, it gives you a unique perspective. It concentrates on the photographic subject, rather than the technology.

(Jeff Rodgers: Yes, you spelled it right. And, thank you for caring.)

Pete Schermerhorn , Jan 05, 2000; 12:43 p.m.

I think what I'm going to start doing - in addition to filter factors, reciprocity (maybe better than reciprocation), etc. - is to take both incident and reflected readings (don't have a spot meter) for all of my photos. If they differ by more than a stop, I'll shoot both readings. Sort of a "reasoned" variety of bracketing. Plus-X film is cheap, and my time is worth even less.

Pete Schermerhorn, in the glorious Berkshire hills of western Massachusetts

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