[JJ_SO]

If you think the truth is rubbish, oh well. They say one never is too old to learn, though.

Well, in your case you passed long ago the moment of willing to learn.

 

And it's so simple to prove you wrong. I just needed to point an f/4 lens to a darker corner - AF was fine. Put the ND8 filter on it - AF started hunting and missed. Of course, bright daylight ND8 is no problem - but with reduced light the ND filter was the reason why AF stopped working properly.

 

Of course it's about the amount of light the AF modules need. If the manufacturer tells me as low as -3EV and I use an ND8, it's then until -1EV without changing any aperture. I don't expect you to agree that would be too far off.

 

But adding a light reducing filter - as NDx and polarizers are - in front or inside the already not super fast lens will lead to struggling AF. Some of the AF points can be used as low as f/8, others as low as f/5.6 and all 51 AF points need to see through a minimum aperture of f/4 and it's not about aperture, only about light quantities.

 

As Markus said to me "Maybe you should occasionally tend to believe people who have actually used the gear they're talking about"