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EXCERPT page containing first few paragraphs. 2023-02-08 03:09:53

Zeiss 28mm f/2.8 C-Biogon

MTF: Zeiss ZM 28mm f/2.8 C-Biogon

Contrast wide open is already very high at center, but exhibits a steep drop-off to the corners. This is a pronouncd wave-type field curvature which persists to f/5.6.

Realistically, the 28/2.8 C-Biogon will be a marginal choice for a planar (flat) target unless stopped down to at least f/8 (a building, distant horizon, etc). In this regard it is similar to the Leica 35mm f/1.4 Summilux ASPH FLE, which has a a similarly strong wave-type field curvature. The zone of sharp focus most likely arcs forward (closer to the camera), then reverses back starting around the edges.

Stop down to f/8 - f/11 for subjects where sharpness across the field is needed. Moreover, a focus bias to the distance is likely to better balance total sharpness across the field.

Actual micro contrast is likely close to 80% across the frame—just not in a geometric plane.

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Aperture series 2.8, 5.6 available in full article
Zeiss ZM 25mm f/2.8 Biogon MTF

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