1080 sensor crop

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C. L. John

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1080 sensor crop

PostSun Dec 30, 2012 3:30 pm

Hello, I would love to use my super 16mm lenses on the upcoming MFT vesrion of the camera, could any one from BMCC's tech stuff can confirm an 1080 crop on the BMCC sensor in order to use the above lenses.
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John
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Christian Schmeer

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Re: 1080 sensor crop

PostSun Dec 30, 2012 9:44 pm

If you record in ProRes format, the camera will output at 1080P. RAW output is 2.5k and there is no 1080P crop mode for recording in RAW yet, but you can always do the cropping in post.
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rick.lang

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Re: 1080 sensor crop

PostSun Dec 30, 2012 10:10 pm

Christian Schmeer wrote:If you record in ProRes format, the camera will output at 1080P. RAW output is 2.5k and there is no 1080P crop mode for recording in RAW yet, but you can always do the cropping in post.


When the BMCC records in ProRes and DNxHD at 1920x1080, I would think the BMCC is starting with the raw data from the 2432x1366 active bayer sensor, converting that to the debayered 2400x1350 image internally and then downscaling the resolution of that image to 1920x1080 for output to the SSD and the ports. So any lens needs to have an image circle that will cover the full active sensor size, 15.81x8.88mm, whether it is intended to deliver a raw image or a compressed HD image.

If you did select raw output from the BMCC, then the debayered 2400x1350 image could of course be cropped to a smaller size but you are losing a lot of quality and resolution. If you do not crop the debayered image, but render a digital intermediate like ProResHQ 4:2:2 or generate a final deliverable in HD video, your application is then downscaling the larger image to 1920x1080.

The only time you might plan on cropping all your footage would be if you wanted to reframe the images for purposes of composition or you want to remove the vignetting from a S16 camera lens that didn't cover the area of the BMCC active sensor as the OP might do.

Rick Lang
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Christian Schmeer

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Re: 1080 sensor crop

PostSun Dec 30, 2012 10:24 pm

Sorry, you are right, otherwise recording in ProRes would always result in an even larger crop factor than 2.3x. I guess recording in RAW and cropping in post is the way to go then, at least until different crop modes become available via firmware updates (which may never happen).
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rick.lang

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Re: 1080 sensor crop

PostSun Dec 30, 2012 10:55 pm

Christian Schmeer wrote:Sorry, you are right, otherwise recording in ProRes would always result in an even larger crop factor than 2.3x. I guess recording in RAW and cropping in post is the way to go then, at least until different crop modes become available via firmware updates (which may never happen).


I know for some people raw processing may not be desirable due to time constraints or budget constraints or other factors, but where it is feasible, I think people will find recording in raw gives them greater flexibility not only in terms of grading but also the occasional reframing or motion tracking for a shot. But generally speaking in my opinion: you crop, you lose.

I'm sure when the community has more experience using ProRes from the camera and uncompressed raw from the camera, each person will be able to judge which situations benefit each option. For example, most commercial and narrative work and any visual effects really deserves raw; event recording like a sports event or music concert may be fine with compressed footage. Weddings are harder to judge but the bride will want raw if she knows it is an option.

That does run contrary to some of the very experienced people who have said words to the effect: "I challenge you to see the difference between the uncompressed raw and ProResHQ 4:2:2." I agree on final output there may not be much difference, but I am convinced (in my ignorance) that working with raw as long as possible will still produce the better look during the edit and grading process and for the final deliverable. Storage does become an issue and I think there may be merit in compressing the original raw via Cineform just for long term retention. Although when I think about it, at the rate hard disks continue to fall (like $129 for a 3TB Western Digital My Book and cheaper for the bare hard disk), and considering how timeless and valuable your creative efforts are, it may even be worth keeping the raw... Just try not to have 10:1 shooting ratio! Documentarians shooting 100:1 better shoot ProRes!

Rick Lang
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Rick Lang

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