EXCERPT page containing first few paragraphs. 2019-02-22 11:43:29
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Sony’s press discussion places very strong emphasis on MTF of 50 line pairs per mm (lp/mm) in the new G Master (GM) lenses. But its approach is self contradictory, and without any rigor:
- Sony MTF chart is at 10 and 30 lp/mm... where is the 50 lp/mm data emphasized so strongly in the Sony press conference? This kind of disconnect undermines credibility. MTF at 50 lp/mm (or even 40) is far more demanding than at 30 lp/mm.
- Sony MTF is computed from a design, not measured from a real lens. Real lenses have to be built, and can at best only approach the theoretical computed performance and only if built to perfection. When actual lenses are examined in field use, weaknesses pop out.
- Sony MTF does not take diffraction into account. While this no bearing on the f/1.4 chart, the f/8 chart is pure fantasy (impossible). It tells us to expect strong performance at f/8, but it does not tell us what a real lens measured will deliver. At f/8, MTF of the Zeiss Otus 85mm f/1.4 APO-Planar (best 35mm lens ever made) even at 40 lp/mm falls short of 80% MTF. Another ding to credibility—it’s not real. Moroever, in real field conditions, internal reflections can drop MTF at f/8 significantly.
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