AF and colours

Can AF be confused by the colour you ask it to use to lock onto? I'm trying to take a shot of some gladioli (I think) which are bluey purple and it doesn't look sharp. I can't make up my mind if it's;

Flat lighting causing the impression of not being sharp
Camera shake at 60th
Poor AF
Or with a 35mm lens the DOF is insufficient at a couple of feet at f3.5 to let anything much be in focus apart from teh exact plane of focus

So, the question is can the colour of the subject affect the focus point of the AF?

Mike

i dont know about the colour having an effect, but I know that the lighting can have an effect.

As far as DOF ....at 2 feet your DOF will be approx 1.5 inches.

Well I went back and shot again in bright sunlight at higher shutter speed and smaller aperture and it wasn't really all that different in many ways except everything was more vibrant so I'm not sure what to make of that. I think it was probably the shallow DOF that made me wonder about the focus and maybe some camera shake too.

Thanks for your thoughts.

Mike

First be sure you eliminate everything else that might be contributing... i.e. put on tripod.

If you can bring the subject inside with controlled lighting and no wind, that would also help.

Color should not affect AF, but if the subject has low contrast the AF might be locking slightly off from where you expect.

The AF sensors are not tiny dots, they are rectangles that extend as much as 20% or more of the viewing area's height. That can lead to a large range of possible focus points to lock onto if the subject is not a flat piece of paper.

I think you're right. I think it was probably very subjective to begin with as the flowers were in flat light which never creates the impression of a sharp image and then the focus lock may well have struggled to find a sharp edge and chose a surprising one.

Down to experience I think.

Mike