Centre focus DOF..how to?

sunbeam · Jul 29, 2009

I was reading a previous post, op had used a very large aperature (1.4 I think) for their pic, and some people posted something about setting a centre? focus, which focus' on the eyes. I can't find the post to save my life, so could someone share with me exactly how one would do this? (I have a pentax if that matters??) Thanks so much!!

Samanax · Jul 29, 2009

I'm not familiar with Pentax DSLRs...check your manual to see if you can manually select the focus point used. Not sure what that has to do with a f/1.4 aperture though.

sunbeam · Jul 29, 2009

The posters were saying if you set your focus, or something, you can focus in on the eyes, to make them 'pop'.

Big Mike · Jul 29, 2009

Focus is plain physics. What you (or your camera's auto focus) actually focus on should be sharp...and so should anything that is exactly the same distance away from the camera. When you use a large aperture (small F number) your DOF (Depth of Field) might be very thin...so things that are closer or farther than your focus point might be out of focus.

So for example, if you are shooting a person and using a large aperture (thin DOF), you will almost always want the eyes to be in focus. So if you focused on their nose, or something else, their eyes might not be sharp.

So if you want to take your photo, without the eyes being directly in the centre where your AF point is...most cameras will allow you to use another AF point, so that you can focus on something that is not in the centre.

Or you can focus on the eyes, lock the focus, then recompose the shot to fit the composition you like.

sunbeam · Jul 29, 2009

THANK YOU Big Mike! I'm definately going to mess with that, locking the focus, 'specially since I tend to have tiny, squirmy little subjects

Big Mike · Jul 29, 2009

Just be careful that your subjects don't move when you lock the focus...because if they move, they likely won't be in focus any more. That's one reason it's hard to shoot kids with a shallow DOF.

Sometimes you have to take a lot of shots and then look for the ones that are in focus.