Thread: BM Pocket 2 with Full Frame lenses - understanding crop factor

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  1. #1 BM Pocket 2 with Full Frame lenses - understanding crop factor 
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    Hi All,

    Curious for those who have used the MFT sensor with full frame lenses in the past, what the crop factor would be with the new Pocket 2 with an EF to MFT adapter?

    Still trying to wrap my head around how the math on all that works as I haven't had any practice using those lenses on that sensor size.

    Thanks!
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  2. #2  
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    A couple things:

    As far as magnification is concerned, full frame lenses and MFT lenses at a given focal length behave the same.

    The core difference between full frame and non-full-frame lenses is the projected image circle. Full frame lenses have a large image circle to cover the larger sensor.

    There are other differences in terms of things like optimization (many lenses have visual aberrations towards the edge of their image circle, or they may have soft spots in the middle) but for a given body all 50mm lenses will give you nearly the same framing regardless of the format they were originally intended for as long as you can adapt them to the mount. (I have Pentax medium format lenses that I can adapt all the way down to MFT, for example.)

    That said: the crop factor on the Pocket4k's sensor is 2.08.

    This means that to achieve equivalent framing on the Pocket4k, as compared to a full frame camera, divide by 2.08.

    So let's say you want the look of a 50mm lens, classic neutral look, natural framing, and distances. You'll want a 50 / 2.08 = 24mm lens.

    If you want to go in the other direction, figuring out how your full frame lenses will behave, just multiply instead.

    Your 50mm lens will behave the same as a 50 * 2.08 = 104mm lens.
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  3. #3  
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    Quote Originally Posted by sohara24 View Post
    Hi All,

    Curious for those who have used the MFT sensor with full frame lenses in the past, what the crop factor would be with the new Pocket 2 with an EF to MFT adapter?

    Still trying to wrap my head around how the math on all that works as I haven't had any practice using those lenses on that sensor size.

    Thanks!
    With a Speedbooster It becomes basically an S35 sensor. Which is the best reference when discussing lens lengths with film people. That's another great reason to add one.
    That 2.08 crop factor reference is against FULL FRAME. So if you're making videos then you can only compare that to using a Sony A7, a Canon 5D, or an ARRI 65. This is not a reference that film and video makers use hardly ever except when using Full Frame video cameras which are extremely uncommon in the list of available video cameras out there.
    I know a guy who got so sick of dealing with cop factors and variances that he said "Screw it!" and bought a pair of Optimo zooms!
    Cameras: Blackmagic Cinema Camera, Blackmagic Pocket Camera (x2), Panasonic GH2 (x2), Sony RX100 ii, Canon 6D, Canon T2i,
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  4. #4  
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    You could also mount the speedbooster for the pocket, and make it nearly a full frame crop though. Andrew Reid did that with his GH4.
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    Instead of thinking in terms of crop factor, learn what is the normal focal length for a given format then figure wide and telephoto from there. a good rule of thumb is roughly half of normal is wide and double normal for telephoto. Fill in gaps accordingly and go to extremes on either end, but it is usually easier to get super telephoto on small sensors than extreme wide.

    FF - 50mm
    S35 - 35mm
    MFT - 25mm
    S16 - 17mm

    As stated MFT becomes essentially s35 when using a standard .7 speedbooster, making it a versatile format.
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  6. #6  
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    Hi Foldablehuman,

    Thanks for the specifics.. that makes sense.

    DPStewart, polaroid and dop16,

    Thanks for the speedbooster info. I was looking into those. I was really close to picking up a UMP, but decided to wait until NAB to see what came out.. now for the price and features, the pocket is insanely attractive. But I did want to use full frame lenses as I see that as more of an investment than the camera tech (since that's changing so rapidly). Getting close to S35 is awesome to hear. Isn't that what the UMP is anyway?
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  7. #7  
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    Quote Originally Posted by polaroid22 View Post
    You could also mount the speedbooster for the pocket, and make it nearly a full frame crop though. Andrew Reid did that with his GH4.
    The GH4 has a smaller sensor than the GH5S or the new Pocket camera, so the BMPCC Speed Booster is going to vignette when you put it on the new Pocket Camera 4K, you need the MFT 0.64 or 0.71 SB. Even the O.64 will vignette wider angle APS-C lenses, like the Tokina Zooms at wider focal lengths. This has been tested with the GH5S.
    Cheers
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  8. #8  
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    Seems irresponsible of grant and the rest of the blackmagic team to say there is basically no crop factor. They should be calling it what it is.
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  9. #9  
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    On a side note, I find it interesting that in all of the promo shots and in all of Grant's interviews the Pocket2 always has an Oly 24-40mm on it

    I understand their choice from an aesthetic perspective it looks good on the camera...almost like a system.
    But I have one pretty much always mounted on one of our Micros.
    It's kind of a perfect "all around" lens for this camera - a relative 25-83mm 2.8, it will allow for push AF and has great two stage manual focusing and it's the sharpest zoom I've shot with.
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  10. #10  
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    Quote Originally Posted by Steven6d View Post
    Seems irresponsible of grant and the rest of the blackmagic team to say there is basically no crop factor. They should be calling it what it is.
    Well, crop factor is entirely from an arbitrary reference point anyway, and from the point of view of the MFT mount it has no crop factor. Since MFT lenses, particularly zooms, will all be in focal lengths appropriate for the sensor there's no additional crop factor that needs to be kept in mind. It's a distinction because the Pocket and Micro, with their S16 sensor, had crop factor relative to the MFT mount.

    The main reason why full frame is used as the reference point for generic crop factor is because all the old guard grew up learning lenses and framing on 35mm photography, and crop factor was a non-technician's issue in digital photography before digital cinema, compounded by the popularity of the 5D and prevalence of relatively accessible Canon/Nikon full frame lenses.
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