 Sarah-fiona |
Basic focusing query I'm using a Canon 350D. I want to take some general photos of my garden where there are flowers from front to back. How can I take a picture where everything is in focus. I have tried using a small aperture and/or a faster shutter speed to prevent blur on a windy day. Where exactly should I be focusing through the viewfinder - a third in? I've experimented with the focusing but can't get everything in focus at the same time. Nothing I try seems to create a focus where everything is in focus. Thanks!
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Alan N. Marcus |
Hi Sarah, While many factors are involved with depth-of-field, here are the basics: Use a tiny aperture. The f/numbers are somewhat cryptic because the tiny apertures are represented by larger values. Stated another way: the tiny apertures give the greatest depth-of-field. They are f/32 – f/16 – f/11. These grant the greatest depth-of-field. Your camera may not sport f/32, use f/16 instead. Depth-of-field increases with shorter focal lengths. Set you zoom more towards the wide angle position. Depth-of-field is a span of acceptable focus that extends in both directions from the point (distance) focused upon. Stated another way, depth-of-field extends both for and aft of the point focused upon. The span of depth-of-field is not split down the middle. It extends more to the rear. Actually 2/3 to the rear and 1/3 towards you. To maximize depth-of-field try to envision the span of the vista. Decide the center spot, and then focus half-way between your position and the center spot. Hope this helps. I try but often I espouse marginal technical advice. Alan Marcus
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Sarah-fiona |
Hi Alan, Thanks for replying. Yes, that's pretty much what I've been trying. I used f32 (Canon 350D and 17-55mm lens). When I look in the viewfinder it is obvious I have to choose which part of the view I wish to put in focus. I have experimenting with focusing at the two thirds and one third points and also other variations. Yet my photos still aren't completely in focus. It feels a bit embarassing to have such a basic problem! Anyway I'll have another go next weekend. Best wishes,
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Alan N. Marcus |
Hi again Sharah, You have identified depth-of-field as the problem, it ain’t necessarily so. Most photographers falsely assume smaller apertures are the sharpest. While small apertures like f/32 yield great depth-of-field, sharpness is compromised. A specific aperture is achieved by the insertion of a washer like barrier in the optical path. The volume of focused light rays produced by the lens is abridged by this obstruction. As light transverses the optical path, some rays are caused to brush by the edges of the aperture obstacle. Those rays that come into contact with edges are caused to deviate and thus they stray. Misdirected rays degrade image sharpness. This condition is known as diffraction. As we stop the lens down we increase the percentage of rays that must brush by the edges of the aperture as apposed to those rays that transverse unimpeded. Thus at some point diffraction becomes devastating. Large format cameras require long focal length lenses. These lenses have larger diameters than our 35mm and digital cameras. For these large format cameras, lens aperture can be tiny indeed before diffraction sets in. Often we see display prints shot with 8x10 or 4x5 cameras with lens set to f/45 or f/90. Sorry to report that the 35mm and digital camera, due to the shortened focal lengths involved, can barely tolerate f/16. Actually the very tiny apertures provided by the lens maker are compromises between proving great depth-of-field and tolerated image degradation due to diffraction. Try f/16 for your compromise. I only dispense marginal technical advice. Alan Marcus
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Andy |
If your camera has A-Dep mode, try it.
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Christopher A. Vedros |
Are you using a tripod? If the small aperture is resulting in slower shutter speeds, you should use a tripod, mirror lockup, and a remote trigger or the self timer to minimize camera vibration. Also, is that the standard kit lens, or the f/2.8 lens with Image Stabilization? If it is the IS lens, you should probably turn off the IS for this shoot. While newer versions of IS lenses don't have the problems that older version lenses had when on tripods, if some of the flowers are moving in the wind, they may be causing the IS to adjust focus, thereby throwing other flowers out of focus. I thought of something else that may be completely obvious, but we might as well cover all the bases while we're at it. Is your lens set to manual focus? I've seen people make this mistake when shooting on a tripod with a remote trigger. If your lens has full-time manual focus (meaning you can manually focus with the focus ring without flipping the switch to MF), and you compose the shot and focus 1/3 into the scene, then press the remote trigger, the camera will autofocus on a different point. You need to switch to MF to avoid having the camera re-adjust the focus. Chris Vedros
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