April 25, 2011, 4:11 p.m.
posted by redphone
Create the Maximum Depth of Field
Imagine the kind of pictures you could take if everything were in focus from one foot to infinity? Here's the inside scoop on one of the oldest secrets in photography.
Galen Rowell, one of my favorite photographers, used to create landscape compositions in which both foreground objects and distant elements appeared in perfect focus. The effect is stunning. The viewer can both study a delicate pattern of petals in a foreground flower and marvel at the beauty of outlying mountains. How did he do that?
Galen found a way to capture tremendous depth of field in his images. In other words, he could have everything in focus, from inches away to infinity. You can employ this same technique in your photography; you just have to know the hack.
Three important factors come into play on these types of shots:
- The focal length of your lens
The wider the better.
- The lens aperture
The smaller the better (f-16, f-22, etc.).
- The object on which you focus in the composition
Contrary to expectation, it's not the thing closest to you.
Once you've properly set these adjustments, you can create depth of field that spans from a foot in front of you to the puffy clouds drifting by.
1 Focal Length: The Wider the Better
Galen Rowell usually shot with 35mm film cameras, and often he would use a 24mm wide-angle lens for this type of landscape image. For this hack, I recommend you find a digital lens that provides a film-camera equivalent of a 28mm lens. You can go wider if you want (such as 24mm), but as you'll see, that's easier said than done in the digital world.
Why? Well, the D70 and many other digital SLRs have image sensors that are smaller than 35mm film. That changes the relationship between lens and camera, and the result is that you often have to multiply the focal length of the lens by a factor of 1.5 to get the same angle of coverage that you would with the lens mounted on a film camera.
If you multiply the Nikon 17-55mm zoom lens by 1.5, you get the 35mm equivalent of a 25.5-82.5mm lens. You may or may not care about all of this. But what you do need to know is that you have to find a lens with a film-camera equivalent of at least a 28mm lens for this type of photography. The Nikon 17-55mm zoom on a D70 should work nicely.
If you're shooting with a digital point and shoot, such as a Canon PowerShot A80, then your built-in zoom lens (7.8-23.4mm) has the film-camera equivalent of a 38-114mm zoom lens—not quite as wide as we'd like for this type of shooting. The good news is that Canon offers a wide converter (WC-DC52) for this camera that attaches over the built-in zoom lens. It extends your field of view to a healthy film-camera equivalent 24mm lens. Cool!
In fact, many digital point and shoots accept wide-angle lens attachments. If you're interested in this type of shooting, then you'll want to make sure your next camera has this capability.
No matter which route you choose—digital SLR or point and shoot—get to the film-camera equivalent of a 28mm lens, and you're in business. Scenes such as the redwood forest shown in Figure are captivating when you're able to extend the depth of field to render all elements in focus, from foreground to back.
Extending the depth of field in a redwood forest
2 Lens Aperture: The Smaller the Better
The second factor for extending your depth of field is to use a small aperture. If we go back to the Nikon 17-55mm zoom, for example, it has an aperture range from f-2.8 to f-22. When the aperture is set to wide open (f-2.8), your images will have a shallow depth of field. For this assignment, you want to use the opposite (f-16 or f-22) for maximum depth. You can achieve this by using the Aperture Priority or Manual Exposure mode on your camera. If you don't have these modes available, look for Landscape in your menu of options. It will stop down the aperture for you (stop down is an old photography term for making the iris hole smaller by choosing an f-stop such as f-16).
When you have the aperture closed down to a diameter this small, you're usually going to have long shutter speeds, such as 1/8 or 1/4 of a second, to compensate for the reduced amount of light coming through the lens. These shutter speeds are too long for handheld photography, so a tripod is in order.
If you attempt to hand-hold the camera with these long shutter speeds, your pictures won't be sharp, due to camera shake. The best way to avoid camera shake is to use a sturdy field tripod and a remote shutter release, so as not to jar the camera when you trip the shutter. You can use the self-timer instead, if that's more convenient.
The main thing to remember is to steady your camera and stop down your aperture to f-16 or smaller.
3 Set Your Focus Manually
Now, here's the real secret to success: switch to manual focus mode and focus on an object that's one-third deep in the composition. Think of it this way: if the flower is the closest object in the picture and the mountains are the most distant elements, then manually focus on something that is one-third the distance between them.
Your tendency will be to focus on the nearest object—in this case, the flower. But that won't give you the greatest depth of field. If you're shooting with a digital SLR that has a depth-of-field preview, you can test this theory. Set your camera to f-22 and focus on a point that's one-third deep in the composition. When you initially look through the viewfinder, both the near object and the distant elements will appear out of focus. That's because you're viewing them with the aperture wide open, which shows the least amount of depth.
Now, press the depth-of-field preview button (with the aperture still set to f-22). The image will get darker, because less light is coming through the lens. But if you look carefully, you'll see that both the closest object and the distant elements are now magically in focus.
4 Final Thoughts
Every lens and camera combination has its own quirks and characteristics for this type of shooting. If you're lucky enough to have a depth-of-field preview button, you can actually check your scene before shooting. But even if you don't, with a little experimentation you'll discover that you can stretch the boundaries of clarity to incredible distances. Save this technique for special compositions that are enhanced by great depth of field.