Monday, October 4, 2010
How To Maximize Depth Of Field—10/04/10
When you want more image elements in focus, take control
1. Use a smaller aperture. The first and most obvious way to increase depth of field is to decrease the aperture setting on your lens. Choose a larger ƒ number (like 22 or 32) to set a smaller aperture (and a smaller opening) that will dramatically increase depth of field.
2. Choose a wider lens. All things being equal, you’re probably selecting a lens based primarily on the composition of the scene rather than purely depth of field. That said, using a wider lens will increase the inherent depth of field available. (That’s why some photojournalists use wide lenses and narrow apertures—they can quickly ensure they’ve got a whole lot of sharp area covered.)
3. Move farther away from your subject. If you’re focused at a lens’ minimum focusing distance, the depth of field will be considerably shallower than it will when using the same lens and the same aperture, but focused closer to infinity. So if your composition affords the opportunity, simply step back to get farther from your subject and make more of the scene fall within the zone of sharpness.
4. Use DOF preview to check your progress. Back in the old days you only had two ways to test he depth of field—process your film and hope you had it right, or use the depth of field preview button to verify what was covered by the zone of sharpness. These days you can simply check the camera’s LCD. But for efficiently verifying depth of field right in the viewfinder, the depth of field preview button still works wonders—and it’s still available on many D-SLRs.
5. Use a tilt/shift lens. When maximizing depth of field requires that you go to extremes, consider a perspective-controlling tilt/shift lens to move the plane of focus where you want it. Most times the plane of focus is parallel to the film or sensor plane, but with a tilt/shift lens you can lay it down, say parallel to a tabletop full of subjects you want to remain sharp from foreground to back.
6. In the studio, fire multiple strobe pops to get enough light. Working in the studio over the years, I’ve gone to extremes to maximize my depth of field. Using combinations of the steps above usually does the trick, but in certain circumstances no matter how much finagling you do you just can’t get all the depth of field required. In these situations, I found that increasing the scene’s illumination worked wonders for stopping down the lens and maximizing depth of field. For instance, let’s say you’re working with studio strobes and you’ve got them firing on full power—maybe that’s 2000ws per pop. And let’s say that the correct exposure for the ISO you’re using is ƒ/16 but you’d really like to get to ƒ/32. (In the old days of large format film, I often wanted to get all the way to ƒ/45. Yikes!) Well if you turn off all the lights in the studio and open the shutter, firing the strobes twice will double the amount of light—making the appropriate exposure go from ƒ/16 to ƒ/22. To increase it even further, just keep doubling the light. It’s not just a single additional strobe flash—you’ve got to double it every time. So if one pop is ƒ/16 and two is ƒ/ 22, it takes four pops to get to ƒ/32 and eight to get to ƒ/45. I’ve fired as many as 32 strobe flashes in a single exposure just to be sure I could maximize the depth of field by shooting at my camera’s minimum aperture. When depth of field sharpness is concerned, it’s hard to do too much to get a sharp shot!