Modern cameras are pretty good at determining the proper camera settings for making properly exposed photos, but if you are going to consistently achieve well-exposed images you will eventually need to take your camera out of program mode and make your own decisions regarding exposure. Back in olden times (about ten years ago,) we shot film and couldn’t see our results until that film was developed. I know I regularly threw out a number of slides per roll due to poor exposure, despite using several techniques for determining proper exposure. With the advent of the histogram in digital cameras, there really is no need to improperly expose an image if you are paying attention. DSLR’s and many point and shoots will display a histogram when you play back an image and many will show you a histogram in live view mode while you are composing an image. The histogram is a bar graph that charts exposure by showing you the number of pixels in your photo at each tonal gradation, from black on the left to white on the right. By learning how to read this graph, you can easily make exposure adjustments in the field to insure you will end up with a properly exposed photo.
Watch the accompanying video for a detailed description of how to read a histogram. You may want to pause it when the screen captures appear so you can really study how the histogram relates to each particular photo. The video explains in detail how to recognize an underexposed or overexposed photo and how to make exposure adjustments based on this information. This explanation works fine in photos with average contrast, when you can usually find an F-stop/shutter speed combination that will give you proper exposure without blown out highlights or underexposed shadows. However in very low contrast scenes or very high contrast scenes, you will need an even deeper understanding of the histogram, which I’ll outline here.
In low-contrast scenes, when the entire frame is either in shadow or lit by shadow-free, diffuse overcast light, you will see a histogram that is all bunched up, with gaps on both the right and left sides of the graph (like in the above photo.) Since that bunch of pixels is primarily mid-tones, you’ll want to expose the scene so that the histogram peaks in the middle of the graph, or slightly to the right of middle. I explain this in more detail in my post, Add Blacks to Give Low Contrast Images Some “Pop”.
In high-contrast scenes, you will most likely end up with a histogram with spikes on both ends of the graph, which means you have both blown out highlights and clipped shadows. Changing your exposure settings can fix one of those problems, but not both (if you reduce exposure to properly expose your highlights, you’ll end up with even more clipped shadows.) This happens on bright sunny days when the scene contains both bright highlights and dark shadows (think of the dappled sunlight in a forest.) It can also happen during sunrise and sunset, when the low angle of the sun will cause the scene to have a bright sky and maybe a well-lit mountain, but the sun isn’t yet high enough to light your foreground. In the latter case, you can use a filter called a graduated split neutral density filter to control exposure (more about this in Week 9.) In the former case (like in the below example,) you face a bigger challenge. Sometimes, you can add some fill flash to balance out exposure, but often you are better off recomposing to eliminate either the highlights or shadows from your composition. You might also just need to return to the scene when the light is lower in contrast.
Here’s this week’s assignment:
1) Watch the video!
2) Get out and shoot! First, if you’ve never seen the histogram before on your camera, read your manual so you know how to display it. For this assignment, I want you to shoot in manual exposure mode. Learn how to read the in-camera meter and how to adjust your aperture and shutter speed so that the meter in your viewfinder indicates a proper exposure. In most cameras, you will see some numbers and vertical lines at the bottom of the viewfinder – in my Canon it looks like this:
-2 | | 1 | | v | | 1 | | +2. (The “v” is actually a triangle, and the numbers indicate the number of stops the camera thinks your photo will be over- or under-exposed.)
When you depress the shutter half way, another line will appear. This one blinks and indicates where on this continuum of exposure your current camera settings will get you. As you change your f-stop and/or shutter speed, this blinking line will move. Get it lined up in the middle and take a photo. Check your histogram and see if you need to adjust your exposure settings. Make your changes if necessary and re-shoot, checking your new histogram to see that you’ve accomplished your goal of proper exposure.
3) Post your properly exposed photos to our on-line Flickr Group before Wednesday, February 29nd. In the picture description, explain how you adjusted the exposure from what the camera’s meter suggested. And don’t try to fake it – your picture’s EXIF data will tell your story!
On Thursday, March 1st, I’ll select one photo to critique and mail a copy of The AMC Guide to Outdoor Digital Photography to the photographer. Post your questions in the comments section below.
Thanks for watching, and have fun!
P.S. I have to give a shout out and thanks to Andrew Pappas for helping out with filming this tip – thanks Andrew!
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