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Focus tested
What can I do to prevent this in the future? A double-edged sword in my life is the quantity of cameras and lenses that I purchase, receive, evaluate, use, review. I simply put it somewhere and shoot it. This image is from the actual test I performed for that verification. The center blur here is 1. A shutter speed fast enough to stop any remaining camera movement is required and strong lighting levels should be present direct sunlight is a good choice, office lighting brightness is the minimum. The only difference between the two shots shown was a truly miniscule difference in focus: Notice how the focus tested sharpest focus points of the graphs at the center of the frame show virtually identical sharpness. After the ten AF shots were captured, the lens was switched to manual-focus mode without changing the focus point from that focus tested was last selected by the AF systemthe camera was slid back a few inches on the optical rail, and then a second series of shots was captured, moving the camera one inch between shots.
Or, we may be able to interpolate the position of best focus, and simply move the camera to that distance to snap the actual test image. We then process the blur data from all the shots for each setting, to produce graphs of the sort shown above. While I seldom have a problem with Canon or Nikon cameras and lenses, focus calibration issues are the primary defect I find - especially with third party AF focus tested. We found that we could reduce the variability between shots somewhat by forcing focus tested camera through several focus cycles by half-pressing the release button on the remote trigger we were using before actually snapping the shutter.
If necessary, the manufacturer can make focus adjustments in either the camera or the lens or both. The Datacolor SpyderLensCal focus tested costs more than my ice cream cone box and its contents are not nearly as tasty and owners of a single lens may not be able to justify the cost of this tool. When you use a digital camera as the measurement device, the problem becomes much more complex. Good shooting technique must then be employed. Owning each camera and lens outright leaves me personally on-the-line financially for verifying the operation of each within the retailer return period. You first need a good focus target. A few months before writing this review, I received the Datacolor SpyderLensCal press release along with an offer to receive an evaluation sample. I love getting to use this focus tested, but the logistics definitely get complicated - and my credit line is generally not happy with me as nearly every camera and lens reviewed on this site to date has been purchased retail. None of the trademark holders are affiliated with this website.
Focus tested
This means a stable camera focus tested a tripod-based setup with mirror lockup enabled and a remote release or self-timer is best with the sensor plane parallel to the focus target. One Shot AF mode should be selected. Then shoot it in the lens focus calibration test methodology I described earlier. Again the size of these subject-distance steps can be anywhere from a fraction of an inch to several inches, depending on the particulars of the situation. This procedure was used for all the points displayed. Shoot the focus test.
Or, we may be able to interpolate the position of best focus, and simply move the camera to that distance to snap the actual test image. Happily, the ungainly contraption works beautifully.