Focussing on black things problem

[HMHB]

Does anyone else have problems with their autofocus when trying to focus on black things ? I seem to have great problems with Rooks and Crows and other black birds, the AF tends to hunt around and sometimes just won't focus. It happens on both my long lenses so I assume it's something to do with the 350D ?

 

[denno75uk]

Don't think it's to do specifically with the camera. My 30D has a fair bit of trouble with my black cat. I think it's because the uneven black fur just absorbs light without reflecting enough to provide the contrast necessary to help the AF.
I also find the metering goes awry too as it tries to either expose for the matte black or the brighter background. Never get a good even exposure.

 

[CyBeRkId2002]

I may be wrong but I beleive focusing works by looking for high contrast changes so if you are focusing on a particulrly dark subject with very little contrast I beleive this will prove a problem for any camera. Obviously, the better the camera the more capable it is at handling such situations.

 

[tdodd]

It is all about the contrast, or lack of contrast. Have a look at this article, which explains pretty well how DSLR autofocus systems work....

http://www.focustestchart.com/chart.html

The article is geared towards the Nikon D70 but the principles apply to any DSLR.