DOF in practice and Hyperfocal distance

[silvan schnelli]

How do and how accurately do cinematographers pay attention to their depth of field when filming?

Seeing as depth of field and the intertwined concept of circle of confusions is very situationally based and dependent on very delicate things like visual acuity, viewing distances, print sizes/projection sizes and much more, how diligent are filmmakers in regards to DOF?

How would you calculate the Hyperfocal distance for example? Are there DOF charts or do some cinema lenses have an integrated feature to show this or do people perhaps manually calculate values and if so with what value do they use for the COC?

thank you for your time 

[David Mullen ASC]

The question is “when does it matter?” If you shoot the whole scene at the same f-stop, let’s say f/2.8, then when does depth of field matter? If deep focus matters then you probably would have lit the scene to a higher f-stop. With digital you can see the depth of field effects on the monitor and make decisions like needing to stop down for example.

Depth of field calculations only happen in two scenarios generally — in prep if planning a deep focus shot or miniature photography, or on the set when shooting film if the AC knows the focus was off on that take but wants to know if it is in focus enough to be acceptable. 

[silvan schnelli]

@David Mullen ASC I suppose it would be a nice concept if one were to be able calculate the hyperfocal distance for a camera, but I guess there are too many unknown factors especially in the exhibition portion. 

I do also feel like focus peaking on monitors, which is what I assume you are referring to, must have a similar issue. I definitely don’t know how peaking is calibrated (user can also change the sensitivity) or engineered, but I can imagine that when monitoring DOF on a monitor or even a larger display, it will always be shallower on the big screen.

However, as you did mentioned before sometimes the DOF is calculated. So I am wondering which COC values would be used, would you use the photography chart values or are there other values?

[Joerg Polzfusz]

https://www.photopills.com/calculators/dof
 

https://dofmaster.com/dofjs.html
 

https://dofsimulator.net/en/

[silvan schnelli]

@Joerg Polzfusz

Thank you for the links, although most of those do seem to be catered mainly to photography. However, I did just see, which for some reason I didn’t notice before, that dofmaster does have cinematography section in the selection tools.

In regards to the Alexa mini which has sensor dimensions of 28.25mm x 18.75mm (open gate) and a Diagonal 33.59mm, what Is it in terms “of x/y inch sensor” notation and why is it that?

From what I have seen a 2/3 inch sensor in the cinema section, gives a coc of about 0.02mm, which to my knowledge is the estimated coc of the Alexa mini in terms of cinema viewing.