Understanding your camera’s meter
There are 2 light meter readings in photography: reflected light reading and incident light reading.
In this post, I’ll confine this discussion to reflected light readings, the kind in your digital cameras.
85% of the time, maybe more depending on the metering mode your camera is set on and the scene you’re trying to meter, the meter inside cameras are accurate and dependable.
There are times when it is not. If you pay close attention and wrap your head around this well, you can learn when to trust your camera’s light meter and when shall we say, you should ditch it?
To illustrate, I photographed 2 people:
- Chris in black T-shirt against a black backdrop
- Trevor in white T-shirt against white backdrop
Part 1: Chris in black tshirt against black background
Here’s the setup: I placed one continous light lamp with daylight balance florescent bulbs on the left and set a chair to the right of the lamp.
Without changing the lighting conditions in either situations, I metered the scene and followed the camera meter’s recommendations.
Since I had the camera on a tripod, and camera shake would not be an issue, I left the aperture on the lens the same but I turned the dial to lower or raise the shutter speed according to what the camera’s light meter suggested.
Chris in his black tshirt as you would expect was over-exposed because the meter wants to make every scene it sees 18% gray.
So when I set my exposure based on that, you see the highlight area of Chris’s face closest to the lamp are blown out. No detail.
The histogram shows this as clipped highlights on the right side.
Part 2: Trevor in white tshirt against white background
Here’s what happened. The meter sees a lot of white this time.
Now the meter is again being fooled and is essentially saying,”ooh… too much light, you need to let in less light to make the scene 18% gray.
This time the meter tells me to set an exposure of 1/20 sec @f4.
So when I follow the meter’s recommendation,Â I get an underexposed picture of Trevor.
When detail is lost in highlight areas, you can’t darken or “burn” in that area to recover the details in that area.
Something to be aware of is this: the picture you see on your monitor as you read this post may or may not look properly exposed.
And while I had the lights and backdrops in place and everyone’s attention here, I went a step further to illustrate how reflected light readings are affected by tones in a scene.
This time I had Duby hold my trusty Kodak Dataguide (soon to be a collector’s item from 20 years ago)
Still using the same lighting, here is the rest of the procedure:
- I made the picture on the left based on a spot meter reading of the white square.
- I made the middle picture based on a spot meter reading of the black square.
- For the 3rd pic, I based my spot meter reading on the 18% gray card.
So if you’ve ever been disappointed with your attempts to photograph the full moon at night, this explains it, I hope.
What is happening in that instance is this: unless you’re using a supertelephoto like a 600 mm lens, the moon is a tiny white ball against the dark sky.
The meter looks at the scene and wanting to make the scene 18% gray, suggest that you let in more light. This causes the subtle shadows on the full moon’s surface to be over-exposed and lost. Remember, details lost in highlights can’t be recovered!
Here’s a tip. You’re probably like me. You don’t walk around with a gray card so what can you do when you’re outdoors? Take a meter reading off green grass or worn old asphalt for 18% gray. Works like a charm. Yeah, only thing is, the green grass and worn old asphalt has to be in the same lighting conditions as your subject.
And in case any of you noticed the color in these pictures aren’t that great, I just checked my White Balance setting on my camera.
It was still on the cloudy setting from Sunday when I shot the Festa Italiana.
I’ll show you how to fix the color to make it look better if you comment and you subscribe to this blog.