A little more visual
If possible, get them in the same plane.
If not, split the difference and take several different aperture settings with complimentary setting in ISO and Shutter-Speed to maintain your EV (Exposure Value).
The COF (Center Of Focus) should be on the rear person's eyes ... and then choose the aperture setting that gives you your DOF (Depth of Field). Please remember to consider that this diagram is a "relative" depiction ... and distances vary with focal length and distance to subject.
For instance: Using a 70mm lens ... and the COF is 10 ft. away
@ f/2.8, the DOF is 0.69 ft ... or ~7.5-inches
@ f/4, the DOF is 0.97 ft or ~12-inches
@ f/8, the DOF is 1.96 ft or ~24-inches
The Focal Plane Shift requires you to position the camera so that both subject's pair of eyes are in the focal plane or parallel with the camera's body. Doing this reduces the impact the DOF will have in the shot.
I hope this helps you visualize the scenario. :)
Try and make use of the information provided by the Online DOF Calculator (<- click here)
Wow, O.K. 2 things, welcome back Millz! don't be a stranger, man I thought I wasn't taking many shots! got to keep that shutter clicking my friend. I make a strong effort to at least scan through the forum every day, really helps keep things fresh in the mind.
Second, Don outstanding visual aid! I not only learned more about COF and effects of apreature variation from that slide but I understand it! Thanks.
Sean, you may have it down, but does 'Millz'? It is with this understanding, you begin to resolve focus issues in your images.
Remember this Christmas Shot? You could term it a 'bokeh' shot,
but it is just a very shallow DOF ... 135mm @ f/1.8 @ 4-foot COF. The actual DOF was about 0.02 feet! His eyes were barely within the plane ...
The thing tio keep in mind is that with a shallow DOF ... your COF has to be dead-on. I usually "double-clutch" (autofocus twice), just to be sure, and then "frame" it.
If the rain goes away I may have a chance to do some field work with this info. We may be going to the Columbus Ohio zoo on Saturday. One of the top 10 zoos in the U.S. and we havent been there in 5 or 6 years! It's only 80 miles or so from home, and we are in the city at least once a month or more. Supposed to be mostly dry, cloudy and cool, I am thinking Tokina 80-400 and the 50mm just in case, and traveling light. any other suggestions?
i look throught he forums often just no time to chat..remember these are my cousins pics i just wanted some opinions. most of the stuff your saying i get and don awesome visual. The difference is i would take the shots and change settingas move things around to get them better. You guys are just way more versed than i am so i thought throw them out there and see what happens.
Millz, is she using center-point/spot focus?
also what mode is she using on the camera?