Perfecting Digital Camera Exposure

By Barry Haynes Back to

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It’s critically important to get a correct exposure when shooting with a digital camera. I shoot my digital camera exposures in RAW mode at the lowest ISO I can use and still get the shutter speed and f-stop I want. Although modern cameras have many different exposure options, I have a standard way of shooting that works best for me. I believe that the image itself is the most important thing. That’s why the steps for getting a good exposure have to be second nature, practiced and thought out ahead of time. That allows you to focus on making that all important image!

Five years ago I moved to the Sunshine Coast, just north of Vancouver, BC, Canada. Living here one becomes attracted to the water and the natural beauty that surrounds you. Before moving here, I never was in a sea kayak and seldom found myself in a boat. Now being on the water in a kayak or sailboat or just the ferry that brings us home is one of the things I enjoy most. In the last five years I’ve spent a lot of time learning how to color adjust waves and ripples, color and contrast of water so it looks the way I see it and feel about it when I’m out there on the water.

Choosing your Camera Settings

RAW, not Auto or JPEG

Hopefully you’ll find RAW mode as one of the image quality choices on your camera. A RAW file is exactly what the chip in the camera captures, analogous to your original film in traditional photography. RAW files can have up to 32,768 tonal values per each Red, Green and Blue color channel. If you choose JPEG for your file type, the image is shot in RAW, then the computer inside your camera automatically color corrects, adjusts contrast and converts your image to an 8 bit file which only has 256 possible tones per color channel. That JPEG format has tossed most of the detail in your image, and then the image is usually sharpened and saved in a compressed version that may lose more shadow and highlight details. Because it has more contrast, the JPEG version may look better in your camera’s small viewing window. When you go to improve the image on your computer, by adding shadow or highlight detail for example, that is where the JPEG falls apart. It doesn’t give you the options provided by all those extra shadow, midtone and highlight values that the larger RAW file has. If you use Auto to shoot your images, the camera is picking your shutter speed and aperture for you.

Histogram display On, use a low ISO

You want to set up your camera’s screen so you can see the histogram display of each image right after you shoot it. This allows you to see if you are under or over exposed. Newer cameras, like my G10, show you a real-time histogram display on the camera’s screen while you are composing a shot so you can see ahead of time if you are going to over expose, then change the exposure to correct before you actually shoot. The histogram display shows you a bar graph of the light values in your image. The darker shadow values are to the left and the bright highlight values are to the right. The shape of the histogram graph will be different for each image and depends on the subject matter in that image. With a contrasty scene, like a bright sunny day, an ideal exposure would have histogram values going from the far left to the far right of the graph without any vertical lines at either the left or the right edge of the graph. A vertical line on the left edge of the graph means that you have lost some shadow detail and on the right edge it means a loss of highlight detail.

I always use the lowest ISO setting on my camera if possible. That would be ISO 100 on my Canon Rebel XTi and ISO 80 on the Canon G10. The G10 is a 14 megapixel pocket camera so its sensor is quite small. I’m able to make 30 to 40 inch prints with the ISO 80 setting, but the higher ISO settings are often too noisy for large prints from the G10. The quality of the XTi images is great at ISO settings up to 200 and I’ve certainly shot and used images with the 1600 setting from the XTi, but those require creative Photoshop techniques to disguise the noise in the shadow areas. During my 20 years of teaching Digital Printmaking workshops, I’ve worked with images from many different digital cameras, and I’ve found that the quality of the pixels is, in many ways, more important than the number of pixels. I try to choose cameras that give me the best quality of pixels for the price. Even though my XTi only has 10 megapixels, I can generally make larger sharper prints from it than from the 14 megapixel G10. The key to being able to up-sample an image and sharpen it for larger high quality prints is to get a correct exposure at the lowest ISO possible where the histogram goes across most of the range from shadow to highlight.

Above is the Histogram for an image shot with a Canon Rebel XTi. The Display (Disp on the Canon; Info on some other cameras) button changes the display mode. While viewing a recently shot image, push the button until you see the histogram on the screen. It should appear in the camera’s preview after shooting an image. Many cameras have a mode to show the histogram in color. The histogram above is correct for a normal contrast day, in that it spans the full range of values but doesn’t go vertical on either the left or right.
On this histogram, notice the vertical bar on the right side, indicating this shot is overexposed and is losing highlight details. The picture to the left of the histogram is flashing black in the sky to show the overexposed areas that will be clipped with no detail in the digital file. To correct this problem, lower your exposure until no clipping is shown.

Metering Style, Shutter & Aperture settings

With a digtal camera, I use the camera’s Auto White Balance setting, then tweak it in Photoshop when it’s off a bit. When shooting in RAW mode, the camera’s white balance setting isn’t permanently applied to the file, as it is with the Auto and JPEG settings. You can see the white balance and edit it in the RAW filter later. When the item I want to focus and meter on is not in the center area of the screen, I just point the camera at that item and hold the shutter button halfway down. This forces most cameras to make their focus and metering choices. While holding the button halfway down, I then move the camera to reframe the shot and this keeps my initial focus and exposure setting.

I’ve learned that the shooting style that works best for me is to set the camera to shutter speed priority. With this setting, I pick the shutter speed and the camera picks the aperture setting based on the scene and meter setting to get the correct exposure. One needs to understand the relationship between the two, in that faster shutter speeds stop motion and smaller aperture openings (the larger aperture numbers) give you more depth of field. When shooting in this way, to get the most depth of field, I usually pick the slowest shutter speed that I can use for the type of image.

Underexposing to Save Highlight Detail

When you get to a new exposure situation, take a sample shot or two then look at your camera’s histogram display. It is most common to lose high- light detail on a bright day, especially when shoot- ing in the direction of the sun or when you have lots of darker areas and fewer bright areas within the scene. Look at your sample shots; you’ve lost highlight detail if you have a vertical line at the right edge of your histogram and/or the bright parts of the picture on your camera’s screen flash on and off to show you that these highlights are clipped (lost forever). When this happens, you should set your camera to create a slightly lower exposure, then shoot the scene again until the histogram goes just to the right side and the flashing stops in the bright parts.

An additional advantage of shooting in RAW mode is that if you do overexpose a bit, you can later lower the exposure setting in the RAW filter, and sometimes, if you didn’t overexpose too much, get your lost highlight details back. In JPEG mode these highlight details are permanently clipped.

Another way to solve the loss of highlight detail problem is to set your camera to bracket exposures. When you do this, normally the camera will shoot one exposure at the normal setting, one under exposed and one over exposed. I find that I seldom need the over exposed shot. I’m often not sure if I’ll need to underexpose by, for example, one f-stop or two. I’m often shooting from a boat or kayak and can’t stop to check the details, so first I set the camera to underexpose by one f-stop. I then go to the camera setting for bracketing exposures and set it to shoot three exposures. Since I’ve already chosen to be shooting one stop under, the bracketing will now set the camera to shoot one at two stops under, one at one stop under and one at the normal exposure. This allows me to later pick the exposure that works best. If I choose to, I can also take the highlight values from the two stops under, or one stop under shot and get the shadows and midtones from the normal exposure. To do this would require editing the image in Photoshop or a similar application. Aligning several exposures like this is also much easier if they were shot from a tripod so all exposures are of the exact same crop. A tripod won’t work from a kayak, but I still find it fairly easy to take clouds and sky detail from one exposure and the rest of an image from another.

On Salmon Inlet, BC; taken from my kayak in RAW mode with the Canon G10.

Summary of RAW file Philosophy

Images that you shoot in RAW mode often look flatter than their JPEG counterparts. This is because the camera does no automatic correction on the RAW files. That gives you the most options later when you edit those files using Lightroom, Photoshop’s RAW filter or some other RAW editing application. Your main goal in exposing a RAW file is that it should have a range of histogram values to match the image without losing any values in the highlight or shadow range. For fairly high contrast, you can underexpose a stop or so and still use the shadows. For extreme contrast, you’ll have to bracket your exposures to give you the option of using several exposures for a final art quality print. These techniques will give you good RAW data to shape into your final image in the digital darkroom.

The system I’ve described here can easily be applied to most outdoor situations, and you’ll have a great image to work with when you want to edit it electronically and/or make a print.

Another day on the water, we took our sailboat through world famous Skookumchuck Rapids, straight ahead here. I find the power and beauty in this body of water amazing!

Product Resources: Cameras: Canon Digital Rebel XTi, Canon EFS 10-22MM lens, Canon G10; Printers: Epson 7600, 4000, 2400; Inks: Ultrachrome; Paper: Epson Premium Luster Photo Paper, Epson Matte Canvas; Software: Adobe Bridge, Photoshop CS4; Computer: Mac.


About the Author

Barry Haynes
Contributor
Barry Haynes is a photographer and author living in Gibsons, BC, Canada, just north of Vancouver, where he has his studio and photography gallery. See www.barryhaynes.com for info about his Outdoor Photography, Photoshop/Printmaking workshops,Photoshop books, images and gallery. His Photoshop Artistry: for Photographers using Photoshop CS2 and Beyond, from New Riders publishing, is the 8th edition of this series. See also www.maxart.com.