Thread: Who's good at math? Crop factors for windowed modes on URSA Mini?

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  1. #1 Who's good at math? Crop factors for windowed modes on URSA Mini? 
    Can someone who is better at math than I am figure out the crop factors for the different modes on the URSA Mini? Or is it impossible to tell yet because of specs we haven't been given yet?

    Most interested in 1080 windowed and the 3k anamorphic, just want to be able to tell if I can use S16 lenses in certain modes and how wide the taking lens for my iscorama could be in 3k anamorphic.

    Another math side note - I've got a 1.33 iscorama - if I used that in 3k anamorphic mode would that give me close to 16:9?? When I use it with a 16:9 sensor it gives me 2.40:1 I believe so I was wondering what the math would be on a 4:3 sensor (assuming that's what the ratio would be on the URSA in 3k mode).

    Thanks!
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  2. #2  
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    Quote Originally Posted by FrissionMedia View Post
    Can someone who is better at math than I am figure out the crop factors for the different modes on the URSA Mini? Or is it impossible to tell yet because of specs we haven't been given yet?

    Most interested in 1080 windowed and the 3k anamorphic, just want to be able to tell if I can use S16 lenses in certain modes and how wide the taking lens for my iscorama could be in 3k anamorphic.

    Another math side note - I've got a 1.33 iscorama - if I used that in 3k anamorphic mode would that give me close to 16:9?? When I use it with a 16:9 sensor it gives me 2.40:1 I believe so I was wondering what the math would be on a 4:3 sensor (assuming that's what the ratio would be on the URSA in 3k mode).

    Thanks!
    Here are the horizontal crop factors compared to 135 film:

    Shooting Resolutions
    4608 x 2592 1.42x
    4096 x 2304 (4K 16:9) 1.6x
    4608 x 1920 (4K 2.4:1) 1.42x
    3840 x 2160 (Ultra HD) 1.7x
    3072 x 2560 (3K Anamorphic 1.2:1) 2.13x squeezed, desqueezed it's 2.4:1 crop 1.065x
    2048 x 1152 (2K 16:9) 3.2x
    1920 x 1080 (HD) 3.4x <-- the photosites are 5.5 microns versus 6.5 microns on the BMPCC.

    The anamorphic crop has an aspect ratio of 6:5, not 4:3. It's designed to be used with a 2x anamorphic lens to achieve a CinemaScope aspect ratio of 2.4:1. If you used a 1.33x anamorphic adapter, you end up with 4096 x 2560 and an aspect ratio of 16:10.
    Last edited by rick.lang; 04-19-2015 at 05:56 PM.
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  3. #3  
    Really useful thank you!!
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  4. #4  
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    I'd be happy with a 2.7 crop ala the digital bolex - that will cover s16 plus still have 2K to work with.
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  5. #5  
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    so do we think the 2k or 1080p modes will cover super 16 lenses? can anyone with the ursa currently confirm either way? it would be really cool to be able to use s16 lenses on the ursa mini in 1080p or whichever mode is closest to the super 16 frame size and take advantage of the high speed frame-rates in that mode too!
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  6. #6  
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    Jake, the 2K window on the 4.6K sensor has a horizontal width about 1.5mm smaller than the HD sensor on the BMPCC. Super 16 is 11.95 x 6.72mm so those S16 lenses should cover the window, barely with a 16:9 aspect ratio 11.264 x 6.336mm.
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