Resolution chart—80/2.8

Resolution chart used for test — about 2 meters across

The MTF charts suggest that sharpness will be degraded by field curvature and astigmatism for the Hartblei 40/4 and 80/2.8, but not much by the 120/4.

Please see test notes on the 40/4 page.

Resolution chart

Results here are similar to those from the 40/4 in terms of contrast/sharpness and field curvature.

Contrast at f/2.8 is quite low, and it should be avoided except for a dreamy effect; the effect is similar to that seen with DSLR 50mm f/1.4 lenses, and might indicate spherical aberration (and therefore possible focus shift, though the image crisps up nicely at f/4).

The results show that with a flat (planar) subject:

• unshifted performance is excellent over most of the 35mm frame, slightly weak at the far corners until f/8 (astigmatism);
• fully shifted, the corner and center cannot be sharp at the same time unless the lens is stopped down to the f/11 - f/16 range;
• some trace uncorrected chromatic aberration is present;
• fully shifted, contrast is low in the corners (due to field curvature) unless focus is near the corner;
• astigmatism is unavoidable; even optimal focus for the corner does not avoid it;
• Overall best results near f/16; stopping down to f/22 degrades contrast and resolution substantially.
• field curvature comes into play significantly at about 5mm of shift; the last 5mm of shift is where the field curvature really is seen as a problem (for planar subjects).

Center, focus at center

Center, focus at corner

Corner, focus at center

Corner, focus at corner

Conclusions

Shifted performance on flat (planar) subjects reveals field curvature and associated astigmatism beyond about 5mm of shift, for which stopping down to f/11 - f/16 is strongly advised. For 3D subjects such considerations may be safely ignored.