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MTF for Hartblei 120mm f/4

This is a technical page. Skip it unless you understand MTF. Or see Making Sharp Images.

Most MTF charts plot contrast (MTF) at a distance from optical center, graphing 10/20/40 line pairs per millimeter, not so here.

These charts graph MTF from zero to 200 line pairs/mm, and there is one graph for each distance from the optical center. A distance of 21.3mm is the corner of a 35mm frame; a distance of 30.4mm is the corner of a 56mm X 24mm frame, which is what you get fully shifted 10mm in the long direction.

Note that Canon and Nikon MTF charts only go to 30 line pairs/mm. Zeiss supplies 10/20/40 line pairs/mm for most of its optics. So the charts on this page should be read out to the “40” mark only, to be (somewhat) comparable to the standard Zeiss MTF graphs.

The graphs were supplied by Hartblei, and used with permission.

Red is tangential, blue is sagittal

Hartblei 120mm f/4

The Zeiss datasheet shows Zeiss’s official technical data.

At center, resolving power is very high, reaching out to 100 line pairs per millimeter. Modest astigmatism develops away from the center, and resolving power drops rapidly away from center — not the behavior we’d hope to see. At an offset of 20mm, fine detail (40 lp/mm) simply cannot be resolved; stopping down to f/8 or f/11 is key here.

Hartblei 120: MTF from 0 to 100 line pairs/mm at center
Hartblei 120: MTF from 0 to 100 line pairs/mm at 5mm offset
Hartblei 120: MTF from 0 to 100 line pairs/mm at 10mm offset
Hartblei 120: MTF from 0 to 100 line pairs/mm at 15mm offset
Hartblei 120: MTF from 0 to 100 line pairs/mm at 20mm offset

Conclusions

MTF performance examined near the edges and corners of the 35mm frame is a little disappointing. Possible explanations include field curvature, and field shots show very nice performance on “3D” images, so one can safely ignore these issues and instead be content with the superlative bokeh and color rendition.


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