[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"

[Brightcolours]

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"

Don't be obtuse, this is how PD AF actually works.

 

If you are in daylight and you focus with a f5.6 lens with ND8 filter, AF will work fine.

Now the problem for PD AF. If you try to focus, in same light, with an f8 lens, AF will not be so fine. Why? Because the PD AF turns blind, or partly blind. PD AF with f5.6 sensor points needs f5.6 width to see. PD AF points with f2.8 sensitivity need f2.8 width to see. An f2.8 point will turn blind with f5,6 lens, NO light reaches the AF point at all.

 

Hence: it is not the amount of light that is the problem, it is the aperture size that is the problem. Too small an aperture will block the optical path of the AF system.

 

Of course, PD AF also needs contrast to see patterns to lock onto. But that was not the subject at hand.