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| p.1 #9 · Can someone explain the hyperfocal distance?!? |
Shooting as a way to learn to understand these things is a great idea - it is perhaps the best way to understand these concepts. Fortunately, it is easy to do some really basic experiments related to aperture and DOF and the so-called hyperfocal distance.
(First, though, about shooting at f/16. This can be a great aperture to shoot on full frame. Contrary to what some will tell you about diffraction blur, f/16 produces very sharp images on full frame when you need large DOF. However, if you shoot a cropped sensor camera, be very cautious about stopping down that far since diffraction blur becomes an issue sooner on the smaller sensor cameras. In general, I would avoid f/16 on crop.)
To find out about the effect of aperture on DOF, just do the following:
1. Put the camera on a tripod and compose some reasonable test image that includes subjects at various distances from the camera position.
2. Focus on your primary subject within the scene.
3. Shoot a series of images at apertures ranging from the largest to perhaps f/16.
4. If you want to be a bit more methodical, you can use your DOF tables/software to "calculate" your hyperfocal distance and repeat the process.
5. Spend some time (well under an hour) looking over the results on your computer.
Another great way to understand the effect is to shoot in live view. Here you can press the DOF preview button, zoom in the live view display to 5x or 10x magnification, and pan around the image on the rear display to see a very good approximation of the effect of your aperture choice on elements of the scene at various distances from the camera.
SIMPLIFICATION: A SECRET
Finally, let me share a little secret. From reading some forum posts, you might imagine that lots of photographers are going around making careful and technical calculations of hyperfocal distance and DOF and all the rest and then making precise and accurate choices about aperture on each shot. In general, it doesn't work that way in the real world, where photographers often tend to select aperture in basically three ways:
1. In a shot where the subject doesn't have a lot of depth and DOF isn't really an issue, we tend to shoot at some default aperture that we believe is more or less optimal for overall resolution, corner resolution, and perhaps vignetting. On full frame, this might frequently be roughly f/8, though there are reasons to vary from that a bit.
2. When working a subject on which we want very large DOF, we tend to go straight to the smallest aperture that we feel will produce large DOF and very good resolution. For me, this is typically f/16 on full frame. (There are rare situations in which I might use a smaller aperture, but very rare and they involve acceptance of some tradeoffs.)
3. When faced with a shot in which we want very narrow DOF, we tend to open up as much as we think we can, perhaps tending toward the largest aperture on the lens we are using. (There are some additional factors to consider here, but I'll leave them out in the spirit of simplifying.)
So, simple generalized approach: Shoot at some middle-of-the-road aperture when DOF isn't a major concern. Shoot at the smallest acceptable aperture when you want large DOF. (f/16 on FF or f/8-f/11 on crop). Open way up when you want to limit DOF.