BetterPhoto Q&A
Category: New Answers

Focusing trick

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November 10, 2004

However, it's very difficult to incorporate that design with autofocus, so almost all autofocus zooms are vari-focal: changing the zoom setting changes the focus. Best results are acheived by zooming to the desired focal length setting first, then focus and take the photo without changing the zoom.

Focus-lock and recompose can also introduce focusing error, especially when the subject is very close. Using the wide area AF sensor closest to your subject is more accurate than using center focus then recomposing and putting the subject off center.

Autofocus algorithms generally quit when focus is within the maximum apeture depth of field. (The EOS 1v and 3 film SLRs and EOS 1-series DSLRs have high precision AF that focuses w/in 1/3 DoF) If there is enough light and your eyesight is good enough you may (or may not) get more precise focus manually.

I've read many digital users (on other forums) complain of inherent "backfocus" problems with the Canon and Nikon DSLRs and they send them off to the service centers for recalibration. Personally, I think the cameras are functioning as designed (AF to w/in the DoF) and they are being hypercritical by looking at their images on a monitor at 100%. Per the very helpful Canon brochure, Getting The Most
From Your EOS-1 Class Digital SLR,
"Understand that image magnification affects perceived sharpness:
When viewing images at 100% magnification, the actual image size can be as large as 4 x 6 FEET depending on the resolution of the camera. If your images are regularly printed at 8.5" x 11" or less, the equivalent magnification with EOS-1D Mark II would be approximately 33%, or 25% with an EOS-1Ds. Try printing your images to evaluate sharpness." Also see the section on applying in-camera sharpening or using an editor like Photoshop's Unsharp Mask, to counter the softening by the anti-alias filter.

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November 10, 2004