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Mario Bosanac

working backwards in finding the correct aperture

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So might be having a total brain-fart on how I could do this but for some reason I can't figure it out at the moment.
So I have a shoot soon and the DP will be working on the Alexa Mini with Cooke s4is. On this particular shot, most likely a 50mm, the distance from the nearest to the farthest subject is about 6 feet (as seen from the image below). We have a couple Arri Skypanels and (1) M18 available, along with some smaller 300w lights or so available for motivated practicals and such. 
My question is, the DoP and I want this distance to be in focus (split diopters not an option, a little too extreme for situation). How can I figure out ahead of time which aperture we should shoot at so I will know if we have strong enough lights available that we might be able to get close enough to the actor without blinding the set with light? I don't want to assume we'll have to go all the way to an f/16 or f/22 if we don't have to. Thanks!

Screenshot 2019-05-15 16.56.40.png

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It’s not enough to know the distance between the two objects, you need to know the distance from camera. Once you know that, a depth of field calculator will tell you what stop you need.

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Use P-cam to determine the split. As Stuart says, the distance between the two subjects is incidental. You need the distance from Camera to Subject 1, and camera to Subject 2. If you know the focal length, format and these two distances, any simple DOF calculator will give you the stop needed to hold both in focus.

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Posted (edited)

The sensor size on the mini is roughly the same as an ASC-P dslr like the Nikon D7000. Using the DOF calculator if you are 10 ft. from the front subject, using a 50mm lens at f16, the in focus distance behind the first subject should be 6.2 ft., which will put your second subject in focus. At f11 and 13 ft. from the first subject, the distance behind the first subject in focus should be 7 ft.

Edited by Bob Speziale

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