Better Light 7 manual Selecting a Focus Site

Selecting a Focus Site

There are several factors to consider when select- ing locations within an image for focus verification. The focus-quality algorithm displays the aggregate differences in intensity between adjacent pixels within the selected area; this means that best-focus determination will work best on high-contrast lines or edges. However, any surface lit to show some tex- ture can usually be used successfully for focus verifi- cation, whether it is brightly lit or in the shadows.

Better Light supplies a business card size focus target with new cameras. Click on the side of the card where the lines are perpendicular to the CCD in the camera insert.

Better Light focus card with focus location selected for a horizontal scan.

Care must also be taken when focusing on por- tions of an image containing multiple planes of focus; the focus number and bar graph may indi- cate several distinct focus “peaks” as camera focus is adjusted across each plane of focus, or a single, broader “peak” may be observed that may not accu- rately represent any single plane of focus. Again, it may be helpful to slightly reposition the focus rectangle to eliminate ambiguous readings; zooming the focus magnification in or out may also alleviate confusing displays.

This is usually not a problem for most copy work, where the entire subject is (hopefully) in the same plane, but can be confusing when attempting to focus on narrow subjects at some distance from the camera.

A. High contrast edge focus readout.

B. Low contrast, but acceptable, focus readout.

When capturing three-dimensional subjects,

the location selected for focus verification should contain only a single plane of focus.

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