Autofocus with tele photo and Neutral gray filters

[deepcore]

Hi
Anyone else experience autofocus problems using 100mm or more and a
neutral gray (graduated or otherwise) Cokin or (Cokin style) filter?
Thanks

 

[Garbz]

What camera, what lens, what grade ND filter?

All of them matter.

 

[deepcore]

Minolta 5D with Minolta 100-200 4.5 zoom Cokin P graduated neutral gray filter.

Thanks

 

[Garbz]

Well for starters at f/4.5 you're already in the slow territory. A lot of cameras may tend to conk out at f/5.6 or above, but with a slow lens like that you're already low on light.

I assume your ND grad filter will be used to block the sky mostly, depending on how you are using it. Unless you're filter is crap and noticeably not sharp then all it can do is reduce either the contrast at the focus point, or the amount of available light for focusing.

Is the focusing slower in darker overcast conditions than in the light? Typically the amount of available sharp contrasty light that gets to the AF defines the performance.