EOS 350D and Canon 50mm f1.8

Doug Pardee wrote:

chits wrote:

I am planning to buy this lens and after searching here saw it has focus issue,

What you guys suggest ? My main purpose is to shot portrait of kids and family on holidays,wedding ( night mainly) , Kindly suggest , Does Sigma or Tamron has good wide aperture lens for 350D ?

The problem is that the autofocus (AF) system on the XT/350D is designed for f/4 zoom lenses. It wasn't designed to be accurate enough to handle the narrow depth of field at f/1.8. The AF accuracy varies from camera to camera. If the AF in your camera happens to work well at f/1.8, great. If not, too bad.

Later "Rebel" models — even the XTi/400D — have improved AF systems that provide increased accuracy at larger apertures (at least with the center focus point). The original Digital Rebel (300D) and the XT/350D, however, don't have that.

I've used the 50mm f1.8 and f1.4 on a t2i (550D) and a 10D.  My experience was similar to what I've read across the Internet regarding these lenses.  Specifically, the focus is very inconsistent when shooting wide open.  To quantify that a bit, when shooting wide open you may get 25-50% of shots out of focus, the OOF rate is fairly high.  But you will get some with good focus, so you have to rely on probability a lot with these lenses.  For things like portraits where you can take many shots of the same composition, this is probably not a deal breaker.  You wouldn't want to use those lenses where each shot is unique and any OOF shots are missed shots, because you'll always have a few OOF in a group.  I seem to recall the f1.4 performed a bit better than the f1.8 (it costs 3-4x as much, better build quality, better AF in theory) but it wasn't significantly better.

It also seems like stopping down to f2.8 and above made a noticeable improvement in AF accuracy, so you can trade off focusing accuracy for DoF/exposure if possible.  And yes, I understand the difference between OOF and narrow DoF, so let's not go there.