Basic aperture question

rawfa

rawfa

Veteran
Scenario: 2 actors sitting still on a sofa having a conversations. There is a big windows that casts a lot of natural light over the actors, so low light is definitely not an issue and I can close the lenses down
Shooting workflow: 1 MarkII and one NEX7 with a speedbooster shooting at the same time with a 28mm 1.8, 50mm 1.4 and 85mm 1.8 (both cameras are still on a tripod)
Question: what is the basic aperture / f stop under these conditions for me to have a nice rich DOF without limiting the actors from moving and getting out of focus? I´ve made some tests and got some great results with the 28mm even at f1.3 for general lateral shots where one actors´ body was in focus and the one wasn´t, but I had some issues with the 85mm...when the actor moved his head a little he kept getting out of focus and it would be an insane task to keep pulling focus on such a wide aperture during the entire piece.

Anyway, tips and suggestions are appreciated.
 
What's behind the sofa? I suggest use F4 to F5.6 to keep the actors in focus, make the background as far as possible to create a rich DOF (or the actors as close to the lens as possible)
 
It depends not only on which lens you use, but also what kind of shot it is: a tight shot will have the same DoF no matter if you shoot it with a 85mm from 2m or with a 24mm from 50cm (what changes with a different lens -and camera position- is perspective, and this in turn affects how "recognizeable" the background is, but not how much movement forwards or backwards makes your actor go out of focus).

So, I'm guessing you have a couple of portraits, with an image that is around 40cm tall in the focus plane (85mm at 1.7m), and a medium shot, with an image about 120cm tall in the focus plane (28mm at 1.65m). That medium shot would have a DoF of 23cm if you shoot it at f/1.3. If that is the DoF you want, then for the portrait you want to go to f/11:
http://www.similaar.com/foto/dof/dof2.php?f_x=1.0&f_r=1.77&f_f=1.3&f_ph=1.2
http://www.similaar.com/foto/dof/dof2.php?f_x=1.0&f_r=1.77&f_f=11&f_ph=0.4
Or you can go for a slightly wider shot: make it 50cm tall in the focus plane (85mm at 2.10m) and you can use f/8:
http://www.similaar.com/foto/dof/dof2.php?f_x=1.0&f_r=1.77&f_f=8&f_ph=0.5
 
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Thanks, guys. Good stuff here. I will try these tips out this weekend. I´d like to have a nice DOF but not crazy thin DOF.
Oh, there is a white wall behind the actors.
 
also keep in mind the other choice: focus distance. of course you know how you want the actors framed, but you can frame them that way with any focal length so long as you can move the camera forward or backward, and the choice is that as you get closer with a wider lens, the more background you will see from side to side and top to bottom, but the more in focus it will appear (but actually have the exact same blur), or you can move back with a longer focal length and see less background, and more apparent blur. so blur aside, if you want to see more of the background, get closer with a wider lens, if you want to hide what's in the background, go farther with a longer lens.

basically, skip to 3:00 in this:

 
I´ve shot another episode today and everything was in perfect focus, but I had to keep the aperture at around f2.0 or f2.8 (occasionally I´ve reached f3.) because otherwise I would have to boost the iso over 400 on the NEX7 and it would add grain to the footage. Actually this was probably the first time I´ve ever shot iso 400 with the NEX7 and I´m not sure if this is a coincidence or not but I´ve never gotten so many overheat warnings and cameras shut downs. It was a nightmare and when I was shooting at iso 100 or 200 I barely ever got any overheat warnings...let alone a camera shutdown. I´ve read in a couple of places that faster SD cards help with the overheat issue but since a 32gb card costs around us$150 here in Brazil I would like some reliable testimonies before sinking more money into a bunch of cards without know if it will work.
 
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