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Crop factor talks, one and only place
  • disneytoydisneytoy

    Hi!

    I've been googling, but can't find the answer, If I want to have the same field of view as an 18mm lens on a Super35 camera to a GH-2 m43 frame, what would be the conversion factor?

    m43 is a 2x crop to a full frame.

    Thanks

  • 12 Replies sorted by
  • Vitaliy_KiselevVitaliy_Kiselev

    Check this

    http://www.personal-view.com/faqs/camera-usage/general-camera-usage-faq

    Btw, I want to slightly update this FAQ with some charts, and after this fully ban discussions of crop factor. :-)

  • disneytoydisneytoy

    I did find a partial answer with pics here:

    http://pro.sony.com/bbsc/ssr/show-highend/resource.solutions.bbsccms-assets-show-highend-pmwf3.shtml?PID=I:highend_2011:pmwf3#/35mmSensor

    But I know the crop factor for GH-2 "video" 1080p 16:9 is not the same as for stills.

    Super35 = 24.9mm x 14mm (diagonal=28.6mm)

    "the multi-aspect sensor of the GH2 allows a bigger 16:9 extraction"

    So what is the actual dimensions of the 16:9 GH-2 extraction?

  • PsycoPsyco

    Taking the numbers from the Sony add, the crop faktor from super 35mm to m4/3 is 1,4x.

    So if you want an 18mm FoV, you will need... 18/1,4 = 12,85 -> a 13mm lens.

    I think the small difference between 4:3 to 16:9 mode on the Gh2 can be neglected.

  • nomadnomad

    There is a pretty good simulator on the website from Abel Cine.

  • PsycoPsyco

    http://www.abelcine.com/fov/

  • jrdjrd

    The usual dimensions given for the Gh2's sensor, when shooting 16x9 video, are 19mm x 10.7mm, which is larger than standard format m43.

    Assuming Sony's figures for S35 film scaled to a 16:9 ratio, 24.9mm x 14mm, are correct (you see a range of figures, sometimes reflecting the difference between aperture size and projection area), then the crop factor is 1.3

    In any event, an 18mm lens on a S35 aperture which measures 24.9x14 will need a 13.7mm lens on a 19mm x 10.7 sensor for equivalent FOV.

  • PsycoPsyco

    @jrd isn't it more like 18.9mm wide? ;-)

  • jrdjrd

    @psycho

    Well, hell, while we're at it, the figures for a 35mm 1.85 ratio, normalized to 16:9, should be 20.96mm x 11.84mm.

    So if the Gh2 sensor is indeed 19mm x 10.7mm, the crop factor there is only 1.1x -- contrary to popular belief!

    Now let's just hope all the numbers are right....

  • disneytoydisneytoy

    Isn't the frame width more important? if you change the aspect ratio from 4:3 to 16:9 for video, and then end up cropping to 2.39, the frame width would be the same not the height? or am I wrong

  • jrdjrd

    @disneytoy

    All these figures assume you start out with either a S35mm or regular 35mm film frame, and then crop that frame as needed to obtain a 16:9 aspect ratio, using the full width of the frame, to get the largest imaging area possible.

    So you're comparing the largest 16:9 frame you can get from any given film frame format, to the GH2, or any other 16:9 based sensor, and determining how much wider a lens you need on the GH2, to give you same the picture, height and width, you're getting on the 16:9 cropped film frames.

    If you're trying to compare the S35mm 2.39 format with the 16:9 Gh2 format cropped to 2.39, that's an entirely different calculation.

  • disneytoydisneytoy

    A director who shoots a lot with an 18mm lens on a super35 sensor. The result is a 2.39 ratio. Say the shot includes both sides of a street and a door way. To get the same field of view with the GH-2s video frame cropped to 2.39 to 1 from the same camera spot. I'm guessing the width of the frame is what we are calculating. S35 = 24.9mm and GH-2 = 19mm would be 1.31 to 1. So, 18mm would equal 13.75mm. So either a 12mm 0r 14mm m43 lens would match the FOV.

  • jrdjrd

    On second thought, and assuming that in all cases you're using the full width of the film frame and the sensor for comparison, the crop factor should remain the same.

    So the crop factor of S35mm v. Gh2 would be 1.3, regardless of what ratio you're shooting at (as long as it's not squarer than16:9, anyway), assuming S35mm measures 24.9mm wide and the Gh2 runs 19mm wide.

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