[Editorial Note: This post is the fourth part of Obtaining Maximum Sharpness, and continues directly where Obtaining Maximum Sharpness, Part 3 leaves off.]
• Use Image Stabilizer or Vibration Reduction technology.
I can personally attest to the fact that Canon's Image Stabilizer technology works remarkably well. I've heard the same about Nikon's Vibration Reduction technology. Use lenses with these technologies when they are available to you. If you don't use these Canon or Nikon lenses, you might want to consider getting a gyroscope to attach to your camera, if you can afford it.
• Manually focus your lenses when possible.
It may take longer and be more difficult, but manually focusing can dramatically improve picture sharpness. Camera autofocus systems have mechanical limitations: autofocus systems focus in discrete steps. If optimum focus of your subject falls in the middle of two neighboring discrete steps-- which is the case most of the time--then you can achieve sharper results manually focusing. Further, autofocus systems are less sensitive to contrast than human eyes, and therefore less able to achieve optimum focus. Most autofocus systems are calibrated to achieve focus of about 50 line pairs per millimeter--which is certainly very good, but nowhere close to what good lenses are capable of. Moreover, autofocus systems are dumb: they don't know exactly what you want to focus on; they just focus somewhere within that big autofocus selection rectangle. When you set your autofocus selection with the rectangle covering half of a bird's head, the autofocus doesn't know whether you want to focus on the bird's eye or its cheek feathers--which could be a critical difference when the depth of field is very shallow.
• Use your lens's optimum aperture.
The sharpness your lens is capable of achieving varies widely as the aperture size changes. If the aperture is too wide, the lens is most subject to loss of sharpness from lens aberrations. If the aperture is too narrow, sharpness will be lost due to light diffraction. Each lens has a "sweet spot": a middle point in the aperture size range where it is least affected by aberrations on the wide end and diffraction on the small end. This range varies by lens model, but is generally somewhere around f/5.6 and f/8. By placing your aperture within the f/5.6-8 range, you will have the potential for achieving sharpeness far beyond what is possible at such apertures as f/1.4 or f/32.
• Center the most detailed parts of the picture in the middle of the frame.
Your lens's sharpness also varies widely from center to edge. Most lenses are capable of far better resolution in the center than close to the edges, especially at their widest apertures. Moreover, lenses can vignette the edges and corners of pictures, making for decreased contrast in the details along the photo's edges, which also lessens perceived sharpness. Consequently, you will get the best sharpness results if you place the parts of your compositiion which are most detailed as close to the middle of your frame as possible.
• Use your zoom lens's optimum focal length.
The sharpness your zoom lens is capable of achieving not only varies widely as the aperture size changes and varies from center to edge; it also varies widely as the focal length changes. A zoom lens has a focal length "sweet spot" where it performs most sharply. Toward the shortest focal length the lens will be most subject to certain kinds of distortion, and toward the longest focal length the lens will be most subject to certain other kinds of distortion. At either end, the lens will be more prone to chromatic aberration than in the middle range. Somewhere in the middle the lens will be sharpest. You may have to resort to trial and error to figure out the focal length sweet spot, or you may be able to find the information. Sometimes it is supplied by lens manufacturers; sometimes it can be found in lens tests in magazines or online.
• Use your lens's optimum distance from the subject.
The sharpness your lens is capable of also varies as the distance of your subject changes, though this variation is usually much slighter than the levels of variation associated with the other mentioned aspects of lens use. Again, there is a "sweet spot" distance where your lens focuses best. However, unlike the sweet spots mentioned above, there is no particular tendency of sweet spots to be toward the middle distance. It is mostly a matter of how the lens was designed, based on what the designers considered the priority. Sometimes, these priorities are easy to figure out. For example, macro lenses tend to perform best around their closest focusing distance (though macro lenses also tend to be exceptionally well corrected for the entire range). For most lenses, you will probably need to figure it out through use.
To be continued, soon. There's still a lot more coming.
Gates of the Valley in Spring
All pictures and text are © Mike Spinak, unless otherwise noted. All pictures shown are available for purchase as fine art prints, and are available for licensed stock use. Telephone: (831) 325-6917.
