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Many Photographers for their set of camera and lenses carry a cheat sheet with different MFA settings for different lighting. Tungston at most 2700K typically will cause a shift if AF opposite to say cool Florescent at 5000K+. It really stinks when as a photog you are stuck needing different MFA values for a single lens such that you get oof results when the lighting changes. If MFA using Tungston, and then shoot at cool white, you will if I remember correctly, g t consistent back focus, and visa versa. My original 24-70 mk1 on my 7d (orig) had this issue. The worst part about it was Canon not acknowledging it during the three trips despite me showing a single MFA number could not be used. The amount of time spent chasing them was unbelievable. If they hadn't told me that a single MFA is supposed to work then I wouldn't have pushed so hard. It was not due short long as a single FL displays this phenomenon. Only afterward did I find corroboration online by other photogs who simply acknowledge it and don't try to fix it. So, literally if you only shoot in one type of light, MFA using that type, otherwise pick a Kelvin Temp in the middle of the type of lighting you'll use. Indoor bright halogen works quite well for MFA. Halog n also has then benefit of high CRI (color rendering index) to appease any color sensitivity of the AF sensor. Good luck, but most lenses do afford sing set of MFA across lighting types.
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