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•the focus point shifts SUBSTANTIALLY when stopping down. Or in other words: the lens suffers from residual spherical aberrations (RSA). In close focus situations this is rather poisonous and the problem was affecting images taken at more conventional distances. The user who supplied the lens checked this behavior with a 2nd lens and this focus characteristic was the same here. This is NOT (sufficiently) compensated by the AF. We did AF reference checks during the MTF analysis and there's a decrease in measured resolution (= increase in focus shift) from f/4 to smaller apertures.
当缩小光圈时焦点显著漂移。换句话说,镜头存在残余球面偏差(RSA)。近距离对焦情况下这个问题十分令人讨厌,而且影响在更常见距离上的成像。提供测试镜头的使用者还检查了另一支镜头,发现相同的聚焦特性。这不是自动聚焦AF可以充分补偿的。我们在MTF分析过程中进行了AF的参考检查,在f/4向更小光圈变化时发现了实测分辨率的下降(相当于焦点漂移量的增加)。
在标尺焦点测试中发现,f4缩至5.6再缩至8,每次焦点会漂移1cm左右。
photozone在结论中称:该镜头分辨率非常锐,某些情况下甚至超越其同门师兄24-70f/2.8L II,但由于RSA问题,此镜头成像被扣分至3星,性价比2星半。
对此镜头一直十分关注,正在最后下决心阶段读到此测评,不得不急刹。恳请使用过此头或有条件测试的兄弟提供一手信息,到底是否存在上述跑焦问题?本人在此多谢了。
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