NX200 test shots - lenses, focus, and ISO 400

Started Nov 9, 2011 | Discussions thread
OP Andrew Westlake Senior Member • Posts: 2,928
Top corners as proxy for focus, and curvature of field

Billx08 wrote:

From the comparison crops that I previously posted, the NX200 photo is front focused, irrespective of any greater DoF due to the smaller aperture. The two photos that I posted showed the comparisons where the selected locations (top right corner - most distant from the camera...)

Sadly, your use of the top corners as a proxy for focus falls foul of a not-entirely-obvious issue - that of curvature of field. It's been apparent to us from the start of shooting this scene that those regions are highly variable in sharpness, indeed far more than would be expected. What we also know is that if you compare different lenses on the same camera, those regions vary far more than any other. The obvious conclusion is that curvature of field is confounding the results here, so we don't pay any attention to them. The pertinent point to note is then that the NX200 was originally shot with the Pentax 50mm F1.4, whereas the NX100 used the Pentax 50mm F2.8 macro, which unsurprisingly is better-corrected for flatness of field. So your observations, while initially persuasive, aren't entirely correct.

If you want to compare focus, use the angled ruler at the lower center of the frame; it's a far better indicator.

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Andy Westlake

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