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Nailing focus for larger than s35 formats


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Hey guys,

I've never shot anything larger than s35 sensor and I can usually manage to nail focus on a moving subject fairly easily at apertures of 2.8 or smaller, but I've been asked to work on a project that will be shot on a full-frame sensor (canon 5d3) and I am kind of intimidated about managing focus at the extremely small DOF. I have a good monitor, and viewfinder available, but I've been practicing at home just following my kids around and stuff and it's much more challenging. I imagine we will be using longer lenses to obtain the same FOV (making it even harder) how do you guys manage this? Are there some tricks you could share with me? I've been watching movies shot on 70mm and vistavision and I am blown away by the sharpness of every single shot. Any insight you can offer is greatly appreciated!

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  • 3 weeks later...

Take measurements, hope they hit their marks. It really comes down to the traditional techniques of focus pulling and responding to the action.
DSLR shooting adds an extra element as you probably wont be using as accurate lenses.
I think talking with the DoP or Director and explaining your limitations and that you might require more stop compared to S35 shooting or shooting on a production camera with cinema lenses.

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2 hours ago, Chris Steel said:

Take measurements, hope they hit their marks. It really comes down to the traditional techniques of focus pulling and responding to the action.
DSLR shooting adds an extra element as you probably wont be using as accurate lenses.
I think talking with the DoP or Director and explaining your limitations and that you might require more stop compared to S35 shooting or shooting on a production camera with cinema lenses.

Now that I've had a few weks to practice with this camera package, I have found that the 5D3 sensor is capable of shooting at much higher ISO with less noise than the 7D because it uses 3x3 pixel binning instead of line skipping. So a lot of the noise get's binned out in camera. This has allowed me to shoot deeper stops with the same lighting setups. It seems like If I shoot for 5.6 I have about as much DOF as 2.8 on a S35 kit. couple that with the fact that the HDMI out is a true 1080p it's easier to see critical focus on a monitor or EVF too.  feel much more confident now. Thank you for your input

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21 hours ago, David Mullen ASC said:

Technically the difference is 1.5-stops in depth of field if comparing a 24mm wide sensor to a 36mm wide sensor, the same as the crop factor. 

So if I understand this correctly, if I wanted the same DOF as 2.8 (s35/aps-c) I would need to stop down to a 4-5.6 split (FF) ?

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Yes, though there may be other factors. If your 7D recording is fuzzier, softer it may seem to have more apparent depth of field. It’s not really more depth of field but if your 5D image has more sharpness and edge contrast, the fall-off into the out-of-focus area may seem more rapid in comparison to the 7D. So if you feel 2-stops is a better match just to be safe, that’s fine.

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