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nebraska focus racking


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#1 Ray Equis

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Posted 11 June 2015 - 09:27 AM

just watching nebraska again. i wonder if this shot is solely focus racking or a change in aperture as well - 0:51-0:54 - do you calculate this in advance or is it just trial and error?. whats up with the image compressing laterally when the focus changes back to the front seats?.
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#2 David Mullen ASC

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Posted 11 June 2015 - 10:40 AM

I don't think there is an iris rack though in the D.I. the colorist may have tried to pull a little bit of overexposed detail down once the focus shifted to the background, but I didn't really see a change.

 

The stretching laterally is an artifact of classic rear-anamorphic prime lenses.  Early CinemaScope lenses had a problem where when the lens was focused to near minimum, the amount of optical squeezing was decreased to less than 2X, but in projection, with a constant 2X lateral stretch, those shots, mainly close-ups, looked fatter.  

 

So Panavision solved the problem of "CinemaScope Mumps" but it meant that to keep to point of focus at a constant 2X horizontal squeeze, the out-of-focus areas would get more than a 2X squeeze, so they look skinny even after the image is stretched back out laterally by 2X.  So when you do a focus rack, you see the amount of squeezing shift as a form of lens breathing.  The only way to minimize it is to stop down the lens a lot to reduce the amount of frame that is out of focus.


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#3 Ray Equis

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Posted 11 June 2015 - 11:00 AM

thanks david nice background info!
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