Auto Focus When Shooting Portraits

I do have to say, that is quite challenging on the lower end DSLR's, atleast without a focus screen.

The 300D seems another likely culprit. Between it being 2 generations behnd on AF and the kit lens being a little loose inside (as it seems to be), you'de have to expect some issue.

May I also suggest greater care at pre-focusing each and every shot. Don't just fire away in one motion. You could also try multiple pre-focus' before firing.

I seem to recall, this technique seemed to boost my percentage from about 80% OOF to 80% in Focus. Don't know if it's because it eliminated motion blur or has a technical validity, but it did seem to work. Now with all USM focus rings, and mainly using IS lenses, combined with this old habit, the problem seems to have vanished altogether.

When I do flash shots of love ones or memorable events, I stay with F5.6-F8, better safe than sorry.

One way to get sharp focus on the eyes, yet still retain shallow DOF, is to use a longer lens and step back.

The technique of rocking the focussing ring back and forth and finding the middle ground helps, of course.

After thinking about the subject, though, I think I have heard that the "consumer" grade lenses have a rather fast-acting manual focus adjustment which doesn't help. I use "L" zooms on my 20D and have absolutely no problem doing manual focus tweaks with the rocking back and forth technique.

It will only help on lenses with FTM (which the 75$ 50/1.8 does not have).
Still, I fail to understand how random adjustments (sorry, that's how your technique sounds to me) of the AF would yield better results than the AF without 'adjustment'. I think that the L zooms might have more precise focusing in the first place.

Bear in mind that the actual area of the focus sensor is much larger than the tiny red dot in your 300D viewfinder.

My 50/1.8 (old used MKI version) was spot-on with my 20D most of the time - even at the tests I did wide open.
Still, to obtain sufficient DOF I also used it @ f/2.8 most of the time ... with good results.

Best regards,
Andy

Andy, the idea is to use manual focus when you would have problems with autofocus and then re-framing. For example, with the portraits that were the focus (pun intended ) of the problem, you could use manual focus to tweak the focus to be perfect at the subject's eyes without reframing the shot at all. What I would do is rock the focus ring back and forth, looking for equal out-of-focus on each side of perfectly focussed and then put the ring in between the extremes. I usually take several swings, narrowing the total band of movement each time and homing in on perfect focus on the eyes (or whatever else is the point of concern for best focus).

There are many times that focussing aids in the viewfinder (split screen, etc.) won't work for this because they would require you to re-frame to focus and that would cause the same problem again - causing something to be out of focus because of the different distances to the focus point when reframing.

With my old Nikon F cameras (that have interchangeable focus screens), I would most often use a plain ground glass focussing screen for the purpose of using this technique.

If you focus on the eyes with the centre AF point and then rotate the camera to recompose there will be a small change in focus of the eyes unless you rotate the lens around its nodal point. This is seldom done. First, try to use an AF sensor that is over the eye when the image is composed, so there is no or minimal movement of the camera before shooting. Second, review the focus manually before shooting. Unfortunately you are using the 50/1.8 lens that does not have full time manual focus override (FTMFO) so you will have to move the AF/MF switch before adjusting focus manually. (I do not purchase lenses that do not have FTMFO.) Thirdly, use a smaller aperture so you have more depth of field so any focus errors will be less noticeable. If you want to blur the background, move the subject further away from the backdrop and use a backdrop that doesn't have any distracting features.

I trust that you are using a tripod if you want to be precise about focus and composition.

Maybe my math is bad. If DOF is between 4 1/2 and 5 inches, doesn't that make for 1/2 inch of focus. Assuming an inaccuracy of 1 inch, it wouldn't be well within the DOF.

Also, 1 inch is for tripods or someone being extremely careful handholding, if you are doing a full body shot, meaning that the focus point on recompose could be as much as 2 to 2 1/2 feet lower on the body.

Having done it myself recently, and not taking extreme care handholding I think I was off by as much as a couple of inches, maybe even 3 on some occasions.

It's not just 50 mm 1.8 issue. I jumped into this thread because of my issue with a recompose shoot I did with a 70-200mm 2.8 IS.

It was outside-inside. Outside in the bright sun, most of my f-stop numbers were 4 or higher (I shoot AV mode virtually exclusively) and more than half of those recompositions the face and eyes were still in very good to excellent focus.

Inside even with 2 500 watt lights with Rosco diffusion paper and a third spot light, I shot mostly at f-stops of 2.8, 3.2, and 3.5 to keep the shutter speeds up, (until I realized that I had forgotten to bump up the ISO even then I first went to 400, but couldn't really use f-stop numbers between 4 and 5 until I went to 800.)

On those shots, I had a very, very low (3 shots out of 80) success rate of keeping her face in focus. I took some face only shots, no recomposing, nearly all those came out fine.

It was my first glamor shoot, no help, so I was concerned about many things, (especially the lighting) I didn't focus (no pun intended) on my recomposition technique. I do it better from now on but, recomposing of the center AF has its drawbacks.

However, I also came away with 2 lessons for myself (at least ones relevant to this discussion thread):

1. Unless defocused background is critical to the result I want, I will make every effort to keep my f-stop numbers above 4 to avoid narrow DOF issues.

2. I will use other AF points as much as possible to minimize recomposing.

By definition, the DOF is the range in front of and behind the plane of focus that will be "acceptably sharp". Most standard DOF calculators, including the one I used, are based on a circle of confusion derived from what the human eye can see in an 8 x 10 print at normal viewing distance. A DOF of 5 inches means that anything that close or closer to the focal plane will appear just as sharp as if it was right at the plane of focus, when viewing an 8 x 10 print.

That said, I think the two points you made are generally valid for producing consistently sharper portraits. The ability to stop down to F/11 is one of the reasons portrait studios use powerful strobes.