Philip thanks...as Tim mentioned, yes, it is the lens. You will see this happen in film as well. If you want a more perfectly corrected lens your choice should be the 75 Cron. That is a true APO lens and should not exhibit the chromatic aberrations such as 75 Lux. As they say, beauty is in the eye of the beholder

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I will say, I have also in the past used the pre-ASPH 50 Lux and the 75 Lux seems to be far better corrected. Not APO quality, but somewhere in between