100mm L not for portraits?

[Loswr]

...the ol' rule of thumb (although disputed by many), 1/3 of the focal plane in front and 2/3 of the focal plane will be in focus

Disputed by 'many'. In this case, the 'many' would include the field of optical physics.

In the scenario under consideration (100mm, f/2.8, reasonably close focus), the distribution of the DoF is 49% in front of the focal point, and 51% behind it.

Maybe some people have really weird, asymmetrical thumbs.

 

[PureShot]

In my screen your picture is not too bad

 

[privatebydesign]

I think the photo would have look sharper had you focused on the closer of the two girls. It appears more natural if the subject in the background, rather than the one in front, appears a bit soft. (Due to haze and other aerial disturbance, our eyes are used to accepting things in the distance as being less distinct.)

That and stopping down to maybe f:5.6 or 8 should do the trick. You don't want to go so slow that the girls' movement spoils the shot.

good advice, plus, the ol' rule of thumb (although disputed by many), 1/3 of the focal plane in front and 2/3 of the focal plane will be in focus, depending on what aperture you use, so you have the better chance of of the back subject falling in focus than the front one jumping in focus.

Along with Neuro's answer I'd add this very helpful site link. Take a look at the tables in the "CLARIFICATION: FOCAL LENGTH AND DEPTH OF FIELD" section and don't forget that, generally, lens focal length gets shorter as you focus closer, no disputes, just physics.

 

[bholliman]

My key learning here? There are DOF calculators for smart phones!

Just checked, I found 44 on iOS. Awesome! I am not one of those people that can do the math in my head and I sometimes panic or worry when taking group shots as to what to set the aperture to.

Thanks guys!

These DOF calculators are a great reference. When I get a new lens I consult them frequently and do as well if trying to set-up a specific shallow DOF shot.

As you gain experience, you will develop a pretty good feel for what your DOF will be in a given situation and can select an appropriate aperture without having to look it up. I'm in my forth year of photography as a serious hobby and selecting aperture settings now is pretty easy in most situations.

 

[awinphoto]

I think the photo would have look sharper had you focused on the closer of the two girls. It appears more natural if the subject in the background, rather than the one in front, appears a bit soft. (Due to haze and other aerial disturbance, our eyes are used to accepting things in the distance as being less distinct.)

That and stopping down to maybe f:5.6 or 8 should do the trick. You don't want to go so slow that the girls' movement spoils the shot.

good advice, plus, the ol' rule of thumb (although disputed by many), 1/3 of the focal plane in front and 2/3 of the focal plane will be in focus, depending on what aperture you use, so you have the better chance of of the back subject falling in focus than the front one jumping in focus.

Along with Neuro's answer I'd add this very helpful site link. Take a look at the tables in the "CLARIFICATION: FOCAL LENGTH AND DEPTH OF FIELD" section and don't forget that, generally, lens focal length gets shorter as you focus closer, no disputes, just physics.

And when all else fails, http://www.dofmaster.com/dofjs.html. DOF and parameters vary based on the focal length of the lens, aperture, and focal distance... Some combinations are narrower as neuro suggests, however other combinations are quite in the favor of 1/3 in front 2/3 in back... the common characteristic is however no matter how narrow the front/back focus is, there typically is more latitude in the back focus than front focus of the acceptable focus range.