Crop Factor on BMPCC? Quick help here please. :)

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Michael Tiedtke

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Crop Factor on BMPCC? Quick help here please. :)

PostSat Apr 13, 2013 3:15 am

Hello! I'll get right to the point. Super excited for the BMPCC. When choosing lenses for the camera, I know it's a S16 sensor, but I can't find the crop factor anywhere. Searched the web for quite some time now. I've heard 3x, but no one has yet really confirmed this. If that is the case, then will C-mount lenses work with this camera and will it in that case fill up the whole frame? Thanks!

/Michael
“If you make every choice as a cinematographer based on the emotions of your characters, you will hit a home run every single time. Everything about cinematography is emotion.”
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rick.lang

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Re: Crop Factor on BMPCC? Quick help here please. :)

PostSat Apr 13, 2013 3:31 am

Tiedtke wrote:Hello! I'll get right to the point. Super excited for the BMPCC. When choosing lenses for the camera, I know it's a S16 sensor, but I can't find the crop factor anywhere. Searched the web for quite some time now. I've heard 3x, but no one has yet really confirmed this. If that is the case, then will C-mount lenses work with this camera and will it in that case fill up the whole frame? Thanks!

/Michael


Crop factor has been mentioned in other threads here. It is very close to a 3x crop compared to a full-frame 35mm camera.

Rick Lang
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phosphor

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Re: Crop Factor on BMPCC? Quick help here please. :)

PostSat Apr 13, 2013 3:37 am

It is like this. Get the sensor size.

BMPCC

Effective Sensor Size
12.48mm x 7.02mm

in relation to the full frame sensor size

36mm x 24mm

Get the horizantal numbers and divide them like this.

36 / 12,48 = 2,8846...

The result is the crop factor.
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rick.lang

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Re: Crop Factor on BMPCC? Quick help here please. :)

PostSun Apr 14, 2013 12:19 am

phosphor wrote:Get the horizantal numbers and divide them like this.

36 / 12,48 = 2,8846...

The result is the crop factor.


Good luck with getting anyone to remember to use that precise value. Nice to see there is a kindred spirit out there! I tried to promote the BMCC crop factor as 2.277x or even 2.28x for a while last year but gave up when everyone wanted to call it 2.3x. In the long run, the simplifications are close enough and easier to remember but 2.9x is more accurate than 3x for the BMPCC.

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MarcusWolschon

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Re: Crop Factor on BMPCC? Quick help here please. :)

PostTue Apr 23, 2013 8:20 pm

Shouldn't that be the diagonal instead of the horizontal?
(Also note that it's compared to 35mm photo full-frame wich is much larger then 35mm film since film runs vertical=>35mm=long side and photo-film horizontal=>35mm=small side.)
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rick.lang

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Re: Crop Factor on BMPCC? Quick help here please. :)

PostTue Apr 23, 2013 10:21 pm

MarcusWolschon wrote:Shouldn't that be the diagonal instead of the horizontal?
(Also note that it's compared to 35mm photo full-frame wich is much larger then 35mm film since film runs vertical=>35mm=long side and photo-film horizontal=>35mm=small side.)


Marcus, the diagonal is certainly the usual approach but that compares apples to oranges since the aspect ratio of full-frame film is 3:2 and many digital sensors including BMCC record 16:9 natively. So I adjust the full-frame to be a 16:9 aspect ratio as well in my approach. When the aspect ratio is identical, then the crop factor calculation could use the diagonal if you want to do all the math to determine the diagonals. But the resulting crop factor is identical to simply using the horizontal dimensions when you compare apples to apples.

Of course if I was concerned about a lens image circle covering the sensor, I'd use the diagonal.

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MarcusWolschon

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Re: AW: Crop Factor on BMPCC? Quick help here please. :)

PostWed May 29, 2013 6:26 am

I was under the impression that 35mm film is 1:2.33.
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Peter J. DeCrescenzo

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Re: Crop Factor on BMPCC? Quick help here please. :)

PostWed May 29, 2013 3:35 pm

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