BMPC 4K greenscreen "should" be keyable?

[mtheory]

Theoretically, the full frame vs S35 difference should be irrelevant because the actual optical image of the lens will be the same, therefore photographic principles should remain intact in cinema as well.

 

Here the "clown" phenomenon only goes away at 50mm on full frame, nevermind 21mm.

 

 

Question is, if her face was more centered in the "35mm" image ( i.e as it would be on "crop" / S35 ), would it make a significant difference in reducing distortion? I wish I could find a proper focal length comparison on a 7D online with horizontal orientation. I'm 75% sure that it would not make a difference, but I guess I'm fishing for a magical solution that would allow me to shoot close to the actors without distortion.

 

Only actual tests with the BMPC will tell.

[Sean Cunningham]

The optical image won't be the same because the distance necessary to achieve the same framing between Full-Frame and S35 will be different.  The S35 result will match the 7D reference you're looking for.  The actual optical image of the lens is the same regardless of sensor.  Distortion is related to what part of the "optical image" can be seen and the distance from subject you have to be to achieve the framing of a sensor/film that's 36mm wide.

 

Faces are distorted by your own eye as you get closer to them.  How is a lens not going to do the same thing?  The theory behind portrait lenses and their reduced distortion have to do with how they render facial features  in accordance with how our own eye-to-brain interface handles facial recognition.  These lenses simulate how we see faces at the optimal distance for recognition (~15' I think it might be?)

 

At 50mm her nose is still quite pronounced, this lens rendering depth compression close to how our eyes see.  By 100mm she's starting to look like a model/actress and not just a semi-cute girl passed in the mall.  You want to know why some pretty girls could never be models or you see some candid photo taken of a working, high paid model and wonder "WTF?" it largely has to do with how that person looks with appropriate lenses and nothing to do with how they look in real life or standing right next to them.   @50mm she's not even the same girl as at @100mm, if you didn't know her personally or had familiarity overriding what the image is telling you about her features.

 

It should come as no surprise 135mm is where she looks best and this is a classic, go-to focal length for portrait photography.  This minor amount of distortion would be the same with a 50mm at a similar distance but now no longer framed for close-up.

[mtheory]

The optical image won't be the same 

Correct, I meant to say "optical distortion" instead of "optical image" in that sentence.

 

Those 4 center squares at the bottom are the sweet spot with least distortion, so an S35 will naturally take advantage of that.

 

Question is, will it make much difference visually? Only the eye will tell, I have an old Canon 20D lying around with a 1.6x factor, will have to make my own test sometime.