50mm f/1.4 hard to focus question, bugging me...

Hello all,

I own a 20D and recently purchased 50mm f/1.4. Everything was great but I have noticed something. When shooting in dim light with aperture f/1.4, it is hard to focus on certain objects and some takes some time to focus in AF mode. For example, I have trying to shoot a black cat during evening with iso 800, f/1.4, the lens had hard time to focus and cannot focus at times. Is it because the object is black/dark? Also, I was trying to shoot a white handrail indoor with white/cream background and it was also having hard time focusing on it. Has anyone experience this with their 50mm or any lens?

I forgot to mention that if I focus on the black cat's eye (bright and different color than his body), the lens was able to focus quicker.

Please help! Just wondering if the lens is defective...or it is just the object...

Thank you all.

Unless there's some light hitting it, or you're focusing on the eyes or something, there's virtually no chance of that thing focusing accurately, even if you're wide open.

AF needs contrast to focus- period.

AF uses contrast to find the best point of focus. If you try and focus on an area with little contrast (black on black or white on white), it will be very difficult for any lens to find focus. Always try and hit a contrasty area for focus.

Nuff said.

Thank you for clearing that up for me. Thank you. Just want to be sure it is not defective. Thanks.

The 50 f/1.4 has a shallow DOF, so I suggest you first start shooting with appertures like f/5.6, specially when you are near to the subjects. Once you get confidence, go more wide open.

I have had a similar problem and I start to take photos of the same subject (a flower) at the same distance, decreesing each time one F/stop and looking at the resulting DOF and pictures.

Enjoy, it´s a wonderful lens.

To help with focusing, you can use either the built-in flash on the 20D or the focus assist beam on an attached flash unit, even if you don't want flash. There's a custom function (I forget which one) which will prevent the flash from firing.