Chinese Manual Focus Lenses

Started 8 months ago | Discussions thread
OP AeroPhotographer Regular Member • Posts: 102
Re: Chinese Manual Focus Lenses
3

A Quick Check of Field Flatness

Playing with manual lenses has awakened me to an easy way to check field flatness. Look at newspaper(s), grass, or pavement obliquely with focus peaking set at mid or high. Adjust focus so that center is sharp. The shape of the horizontal band of peaking color reveals flatness of field. A straight band indicates a flat field. An arc indicates curvature. An asymmetric band reveals de-centering. Try various apertures.

Bright lighting helps.

Alan

PS: Field curvature doesn't matter for some scenes. But it does matter for perpendicular shots of flat surfaces, like facades of buildings shot with fast apertures. Field curvature tends to vanish with small apertures.

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