Getting good exposures with your digital SLR

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.

In essence when the meter saw all the black in the scene, it was thinking “ooh… way too dark, you have to let in more light to to change the black to gray.

It suggested my exposure be 1/8 sec @f4. On the left is the histogram under Levels in Photoshop. You may not see the clipped highlights at first but here’s a close up of the right side area.

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

For the 2nd part of this demonstration,  I swapped Chris for Trevor who wore a white tshirt. I also switched my backdrop to an off-white color.

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,  I get an underexposed picture of Trevor.

From the histogram below, you can see this time the shadow areas are clipped and most of the digital information is located on the left side.

 

So from comparing the two pictures, you can see that underexposing accidentally is not as “fatal” as over-exposing.

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.

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8 thoughts on “Getting good exposures with your digital SLR”

  1. Thanks Pete for the info. I think I had been doing that myself in a primitive intuitive way. When photographing houses, interiors for listings, I would turn on the incandescent lights, and if I were lucky would have the white balance set right…then if I found the room was too dark, because of a bright window throwing the meter off, I would try to find a “color” mid range to get the room in balance and shoot. Whooda thought?

    Now I will do it being more knowing, and thanks for the suggestion about the asphalt, grass, etc.

    1. Pat,
      That is the gist of it but not entirely. Without looking at the actual images themselves, it is difficult to say if that was the best image you could get in those conditions. Thanks for your kind comments.

  2. Bobby,
    Thanks for visiting the blog and commenting. Good to know you’re getting your money’s worth. Next time you guys do the demo and you can tell me what kind of results to expect.

  3. Peter:
    One of the best things about this class are the demo’s. They reinforce, and aid the learning curve. Knowledge is power.
    Bobby

  4. Jessica,
    Thanks for visiting the blog and commenting. We’re not done with this demo. We’ll continue and discuss incident light reading and White Balance using the same setup next time.

  5. Dwayne,
    Thanks for visiting my blog and commenting. I’m pleased the post helped in your understanding of what your camera’s meter is doing in those instances.

    It is a similar situation when you’re at a concert when the stage is dark but for the lone performer or singer who is being lit by a solitary spotlight.

    If you follow the camera’s recommendation, your singer will be over-exposed too especially if you use the metering mode that is center-weighted. Better cameras have the ability to narrow the area of sensitivity. If you don’t have that functionality in your camera, use your longest focal length lens and fill the frame” with your subject. Then get a reading that way. Spotmeters basically operate that way.

  6. You’re right it really did help to reinforce my experience in class. Thank you very much I will share this blog with other photography enthusiast. Also the link to the blog was helpful.

    Jessica

  7. I love astronomy and have tried to take pictures of what I see but always end up with nothing. This was really helpful.

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