Trouble focusing on eyes with EF 50mm on 450D

[bob_estremera]

<p>Having a pretty consistent problem with focusing.<br />I shoot my 50mm 1.8 lens around 2.8 and use the center focus point, the only one that lights up, on the eyes, then recompose.<br>

Now that I'm doing some retouching I'm noticing that the eyes are not in critical focus. Sometimes what's in focus is the hair behind the eyes, perhaps the necklace, but even though I'm focusing on the eyes, they're frequently not in focus. And I'm really careful about this.<br>

Any ideas of suggestions on my technique?</p>

[evan_goulet]

<p><a href="http://www.outbackphoto.com/workshop/phototechnique/essay06/essay.html">Why focus-recompose sucks.</a></p>

<p>I have encountered this often with shallow depths of field as well. I have since started to focus while the shot is composed.</p>

[bob_estremera]

<p>Excellent Evan, I'll adjust my technique according. But it's going to be hard to select outside focus points when you're trying to move and repose subject and maintain a flow that doesn't exactly favor, "hold it while I select a new focus point!" My guess is that for slow or very deliberate shots, this might work but perhaps shooting at more like f4 or f8 will be more reliable. But then I'd have to crank my ISO up in available light. But thanks again. That was a very illuminating article and I remember reading about something like it before with the new Hasselblad special focusing magic processor of some kind.</p>

[evan_goulet]

<p>Try doing it in low light, with moving children, and manual focus...<br>

That's my usual situation.</p>

[craig_shearman1]

<p>Bob, are you continuing to hold the shutter release halfway down from the time you focus until the time you shoot? If you let it go back up before you shoot, then it will refocus when you push it down again to shoot. I agree that trying to change focus points on the fly isn't always convenient, and there's no guarantee that another focus point will be in the right place so you may have to recompose anyway. Personally, if the subject is sitting reasonably still, I find it easier to focus manually.</p>

[bob_estremera]

<p>Craig, yes, holding it down 1/2 until I shoot. These modern slr's (450D) and their lenses are not the best for manual focusing but I might have to give that a try.</p>

[craig_shearman1]

<p>Current DSLRs, at least he ones I've seen, don't have the microprism ring or split image rangefinder center that film SLRs had to make manual focusing easy. But most that I've used usually have a light that lights up when focus is achieved, both in AF and manual focus. This functions as an electronic rangefinder of sorts -- even if the screen isn't good enough to judge focus, if you focus manually with the focus spot on the eyes, it will confirm that you are in focus, no need to hold button halfway down. Since you don't have to hold the button down, once you recompose it stays in focus for as long as you want to keep shooting without having to go back and forth for each shot.</p>

[bob_estremera]

<p>Craig, I'll try your suggestion above. And as you mentioned earlier, since portrait sessions usually fall into vertical tight headshots, vertical waist up compositions and horizontal (maybe with some space on either side of the subject) I found that knowing what the composition will be makes it easier to use a different focus point for that series of compositions. I got a much higher rate of focus accuracy without much effort. But between your two suggestions, I think I've got it. Thanks,</p>

[Ken Katz]

Another take on focus - recompose (the last example is similar to your set up):

 

http://www.bobatkins.com/photography/technical/focus_recompose.html

 

I would think that the bigger issue may be that the since AF sensors are usually larger than what is marked in your viewfinder, it is difficult to accurately AF on just the eye. Also it is possible that in the time between focusing and taking the photo, either you or your subject moved just slightly, which would be enough to result in some focus inaccuracy.

[snapper_h]

<p>The 50mm at 1.8 or 1.4 has a pretty narrow field, depending on distance to subject, try bumping it to 2.8 for larger (deeper) DOF. After pre composing, click the auto focus off on the lens. I do this rather than locking in the focal on the camera itself (T1i).</p>

<p>Here's a DOF calculator to give you an idea of focal field. http://www.dofmaster.com/dofjs.html</p>