Focus Question

robigouk

Hi

I previously posted a question on here if people use the "*" to pre set their focus when shooting.

My next question is - when shooting does anybody zoom in, focus (I lock using "*") and then zoom out before taking the photo?

I heard that focus isn't always the same a different zoom lengths?

The reason I ask - if I'm shooting a small group of people posing at a wedding, I'm quite far back so I can't be sure if I've focused on the eyes exactly unless I zoom in first?

Any thoughts on this?

kdog

Dude, you seriously need to learn about depth of field. People worry about getting the focus on the eyes when they intentionally use a depth of field shallow enough so that only the eyes are in perfect focus, while the rest of the face is pleasingly soft. You wouldn't want to try that on a group of people because it would be impractical to line them up so that their eyes are all on the same plane. Simply use a depth of field deep enough to encompass the entire group of people, focus on somebody's head in the middle of the pack, and be done with it.

I would suggest you spend some quality time playing with a DOF calculator to see the effects of focal length, distance and aperture on DOF. A wedding photographer needs to know this stuff cold. Link: http://www.dofmaster.com/dofjs.html

Regards,
-joel

JohnBiggs

kdog wrote:

Dude, you seriously need to learn about depth of field. -joel

I won't be so harsh, but I would say that I have read that zooming after focussing can screw up the focus. I've never tried it and I don't know if it's the same for all lenses but to me its just not worth the bother.

As Joel said, with a group of people you have to get the right depth and just focus on a head. I'll typically use f5.6 or f8 for general purpose group shots.

Also with weddings you don't want to get in the habit of doing all that to focus. That could really eat into time no matter how good you get.

bendruckerphoto

You really only need to worry about being exactly focused on the eyes for a headshot or half length portrait at a large aperture. Otherwise, the DOF is long enough for the eyes to be in focus even if you focus on the forehead.

Qarik

robigouk wrote:

Hi

I previously posted a question on here if people use the "*" to pre set their focus when shooting.

My next question is - when shooting does anybody zoom in, focus (I lock using "*") and then zoom out before taking the photo?

I heard that focus isn't always the same a different zoom lengths?

The reason I ask - if I'm shooting a small group of people posing at a wedding, I'm quite far back so I can't be sure if I've focused on the eyes exactly unless I zoom in first?

Any thoughts on this?

If you zoom in an focus..then lock and zoom out..then DOF changes will be off unless the subject are far away enough to be in the hyperfocal distance at both zoom lengths. DOF depends on zoom strength AND distance as well as aperture. You change one and the DOF changes as well.

That said what you described may work if all you do is zoom out because as you zoom out the DOF increases at the same distance. Still it is not the best way.

For the situation you describe you need to simply "know" what aperture and zoom lenght and distance will give you the proper DOF for group shot. That is "getting to know you lens".

I suggest you spend some time with DOF calculator.

Matthew Saville

If your camera is perfectly calibrated, and you skillfully place your focus point, you should be able to shoot without zooming in and out. If you're getting out of focus images you either need better technique, or your camera needs to be calibrated. (Body and/or lenses...)

If you're shooting a group of people and talking about "zooming", I'll assume that you don't need to worry about focusing on someone's eyes exactly like you might with an f/1.2 L lens for a single headshot. If you're shooting at f/2.8 or tighter and you're comping multiple faces or someone's entire body, then you really just need to get your focus point over their face in general, not necessarily their eyes exactly.

Like others have said, it is critical to play around with DOF and see what you can get away with and what you cannot. I've already stated a general rule of thumb, regarding the difference between shooting a headshot at f/1.2 and shooting a group shot at f/4 or something. But, get out there and practice, practice, practice!

=Matt=