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# Depth of field 1

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Created for Springfield Illinois Camera Club by Paul Puckel.

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### Depth of field 1

1. 1. Why is this important? This is what draws theviewer’s attention to what it is that you wanthim or her to look at when they look at yourphotos. It should be that which is in focus.11
2. 2.  Depth of field is simply the zone in front of andbehind the point of focus that is acceptablysharp. Simply, how much of your picture is infocus. We try to impress people with the beautyof our pictures, so we have to know what effectfocus has on the viewer. Depth of field is whatwe use to control what the viewer looks at. 22
3. 3.  Depth of field is controlled by your choice ofAperture, Lens and Working Distance. It is alsocontrolled by your vision of the scene. Aperture as you probably know is expressed inf-stops. There are two numbers you mustmemorize to master f-stops. They are 1 and 1.4.All f-stops are then a mathematical progressionof those two numbers. It goes like this:1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, and 64.3
4. 4.  The closer you are to the subject the shallowerthe depth of field. So if you want to shoot a bee on a flower youcould use a 28mm lens which will give youbetter depth of field but not much closeness oryou could use a 200 mm lens and stand fartheraway. But you would have to stand 10 feetback. Do you know why? Orrrrrrrrrrr, you could use a 200 mm lens witha 25 mm extension tube and get up about 5 ftcloser.4
5. 5.  An aperture, usually referred to as an “ap”, is ahole through which the light from a scene passesto land onto the film or sensor plane. Itrepresents the diameter of the opening as afraction of the focal length of the lens. So forexample, f/5.6 on a 100 mm lens is a largeropening, 1/5.6 100mm than, f/11 which is 1/11the opening of a 100mm. So the larger the f/stopnumber the smaller the lens opening.5
6. 6.  In a visual sense this means that the aperturesare related by size. So, an “ap” of f/2.8 is twiceas wide as an “ap” of f/4.0 and an “ap” off/4.0 is twice as wide as an “ap “ of f/5.6. 5.6 istwice f/8, f8 is twice f/11, f11 is twice f/16,f/16is twice f/22, f/22 is twice f/32, f/32 is twicef/64. How many times bigger is f/4 than f/16?See if you can figure that out. The upshot of allthis is as you go from f/2.8 to f/16 you get halfas much light each time you change f/ stops.6
7. 7.  You can check out the depth of field if yourcamera has a depth of field preview button.When you push the preview button it actuallychanges what you see. When you focus a shotbefore you press the shutter, the lens is actuallywide open so you can see to focus. Pushing thepreview button stops the lens down to the actualsetting you have chosen for the shot. That allowsyou to see what’s in focus and what’s not. 57
8. 8.  So how does lens figure in? There are a lot of factors inyour choice of lens. What is your subject? Time of day?Wind? Stationary object? Subject to distance? You arestanding on an overlook in Yellowstone N.P. using a28mm lens to get a vista shot. If you choose f/5.6 asyour aperture and the closest object is 500 yards awayyou may get an acceptable shot. But if you choose f/32you’ll get a great shot, all other things being equal.Secret: your exposure time is controlled by yourchoice of aperture. Thus your depth of field is afunction of time. The smaller your aperture the longeryour shutter is open; the longer your shutter is open, the greater your depth of field. 68
9. 9.  So if you are trying to isolate a flower youmight chose a 100 mm lens or a 200 mm lensbecause you want to isolate the flower from theother flowers or other foliage. The longer thelens, the shallower the depth of field.Conversely, the shorter the lens the greater thedepth of field. So if you use a Macro Lens youwill get a very small depth of field. Addingtele-converters will cut down your depth offield more as will the use of extension tubes.9
10. 10.  Extension tubes are used for magnificationpurposes and follow a simple formula. That is:ExtensionMagnification = ------------------------------Lens length in MMThey also limit Depth of field10
11. 11.  Speaking of lenses, an important statistic toknow is what is the focusing distance of thelens you will use for this shot? I bring this upbecause it will help visualize the shot. My 70-200 f/2.8 lens stops focusing close up at 10 feet.If I want to get closer I have to add extensiontubes. So read the papers that come with yourlenses. The extension tubes ad magnification.This affects depth of field in the reverse of agrand scenic shot. You use this to isolate aflower, a bug, or some other small subject.11
12. 12.  Depth of field isolates a subject for theviewer, be it a grandios scene, a single objectwithin a wider view or a close up . You control this by a). Lens b). Aperture c). Working distance12
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