Thread: Crop Factor Lens Database

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  1. #1 Crop Factor Lens Database 
    Original DVXuser Thread:
    http://www.dvxuser.com/V6/showthread...tions-go-here)

    Quick table of most popular focal lengths with rough equivalents. Thanks Rick Burnett and Kholi:
    FS100/7D (1.5)
    18mm
    24mm
    28mm
    BM (2.3)
    11mm
    16mm
    18mm
    5D
    26mm
    36mm
    41mm
    35mm 23mm 52mm
    50mm
    85mm
    32mm
    54mm
    75mm
    123mm









    More comprehensive charts:
    Special thanks to "popcornflix" for making the pdf:
    BMD Cinema Camera Comparison.pdf

    Thanks to "Huski" for the following document:
    https://docs.google.com/spreadsheet/...iV0JJLWc#gid=0
    www.bmcuser.com
    A Landmine Media "User" Community
    The online resource for the Blackmagic Design Cinema Camera
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  2. #2 Re: READ BEFORE POSTING: Crop Factor and Wide-Angle Lens Database 
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    This thread's also going to be used to list wide lenses and lens reports from users. So, feel free to start adding your lists of lenses and such.
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  3. #3  
    Senior Member randyman's Avatar
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    I've heard so much conflicting info about focal lengths on the BMC, that I'm going to lay my ignorance out on the line and try to get a final answer once and for all.

    It's my understanding that if we take an EF lens - designed for full frame - and use it on the BMC, we multiply its focal length by 2.31 to get its effective focal length on the new camera. Correct so far?

    So if we take an EF-S lens - designed for a crop sensor, like the 7D - and use it on the BMC, we only have to multiply it by 1.62 to get the effective focal length.

    Am I on track here? Because I've been told I'm wrong, I'm right, I'm wrong... I know you all out there can set this to rest for me. Thanks!
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  4. #4  
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    Hey Randy,

    Rule of thumb: a 50 is a 50 is a 50. That means that even a 50mm specifically made for M4/3 will still be the same 50mm focal length on a Full Frame camera. Or, if it actually covered full frame it would still work on a full frame camera.

    There are some EF-S lenses that actually cover Full Frame at the end of the zoom range, but the performance on a Full Frame sensor may be poor.

    So no matter what lens you use, if you want to find the equivalent for the Magic Cam to APS-C/S35 then use 1.62/1.5 respectively. For full frame, 2.3x.

    Hope that helps.
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  5. #5  
    Senior Member randyman's Avatar
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    Thanks, Kholi - I do understand that despite the intrinsically magical nature of the camera, the focal length of the lens doesn't actually magically change - the smaller sensor just crops the resulting image. Thanks for letting me know my numbers were on the right track.
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  6. #6  
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    If anyone has pCAM it's easy to set up a custom camera by entering the BMC active sensor size and CoC. I use .00056 for the CoC to be safe until BMD says different (.00056 is the CoC for the 3K RED ONE crop). You can then compare the FoV of any lens on the BMC to any other camera with the same lens, just use "Focal Length Match" in pCAM to compare.
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  7. #7  
    Quote Originally Posted by randyman View Post
    Thanks, Kholi - I do understand that despite the intrinsically magical nature of the camera, the focal length of the lens doesn't actually magically change - the smaller sensor just crops the resulting image. Thanks for letting me know my numbers were on the right track.
    As Kholi was saying, a 50 is a 50. So no matter what format the lens was designed for, the crop factor remains the same, because it is the BMC's sensor that is doing the cropping.

    Here's what I mean, and why I think your understanding may be confused... if you were thinking that a 50mm ef-s lens should be multiplied by 1.6, and a 50mm EF lens should be multiplied by 2.31, then you'd be on the wrong track. Because a 50mm EF-S lens and a 50mm EF lens will both produce identical results on the BMC.

    Focal length is focal length, regardless of what camera the lens was made for. Focal length gives you the amount of magnification the lens does. And "crop" is something the sensor does. The only difference between an EF-S lens and an EF lens (as far as imaging goes) is how big of a picture the lens projects onto the sensor. An EF lens can project a bigger picture (more of the picture, not more magnified) than an EF-S lens does.

    Think about it like looking through a window -- an EF-S lens is like a porthole, and an EF lens is like a huge picture window. Both will show you the exact same scene (i.e., looking at a tree out the window will look identical through either window), but the picture window lets you see much more of the scene -- more trees, trees to the left and to the right, whereas the EF-S porthole only shows you a small subset of that bigger picture.
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  8. #8  
    Here's a simpler way to think of it:

    50mm is the focal length of the lens. That's an internal measurement of the lens itself. That doesn't change.

    The Angle Of View (AOV) shows how much of the image the sensor sees -- how much of the image ends up in the picture.
    The AOV for any given lens changes, depending on the size of the sensor.
    AOV is a function of both the focal length of the lens and the sensor size.
    Shorter lenses have wider AOV, and are called "wide angle."
    The smaller the sensor, the narrower the AOV.

    Which means that as you move to smaller sensors (narrower AOV), you need to use shorter lenses (wider AOV) to keep the same AOV.
    That's where Crop Factor comes in.

    Crop factor is used to maintain AOV between two cameras with different sized sensors.
    You choose a focal length from one camera, and multiply it by the Crop Factor of another camera to find a focal length with the same AOV on the target camera.


    Pretty easy. So why do people get so confused?

    It's how people talk about it. Photographers should be comparing AOV, but they are used to discussing lenses in terms of focal length.
    Unfortunately, photographers use the same language to describe two different situations.

    They will say both:

    "A 50mm on a 5D is a 115mm on a Black Magic."

    and

    "A 50mm on a 5D is a 22mm on a Black Magic."


    And both are correct! WAIT -- WHAT!?!?

    Here's why:

    "A 50mm on a 5D is a 115mm on a Black Magic." actually means:

    "If you put a 50mm on a BMDCC, it will have the same AOV as a 115mm on a 5D."

    and

    "A 50mm on a 5D is a 22mm on a Black Magic." really means:

    "If you want the same AOV as a 50mm on a 5D, you need to use a 22mm on a BMDCC."


    So once you bring AOV into the conversation, it becomes easier to be precise.




    Hope that clears it up a bit.
    Last edited by popcornflix; 04-23-2012 at 07:09 PM.
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  9. #9  
    AbelCine Field of View Comparator updated to include BlackMagic Digital Cinema Camera.

    http://www.abelcine.com/fov/
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  10. #10 Croppers 
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    When people are talking about crop-factors, the crop figure is relative to a specific sensor size vs the BMD. Since the BMD has a EF mount at this time, the crop-factor figure most people have been stating (2.3) is relative to the full-frame Canon sensors for which the EF lenses were specifically designed. It's a good basic reference point but ....

    ... If you have been using the 7D, for instance, and are accustomed to that field of view, the comparable crop-factor will be less since the APS-C sensor in the 7D already crops 1.6 when compared to the full-frame 5DMII.

    If and when the BMD camera has a Micro 4/3 mount, people accustomed to using a camera with an M4/3 sensor size will notice very little cropping since the BMC sensor is close to the M4/3 sensor in size. This is why it makes sense to use a M4/3 mount on the BMD. But from an economic point of view, there are probably more EF lenses and Nikon EF adaptable lenses in people's collections than M4/3 lenses. This will likely make the BMD attractive to more buyers since buying new glass is an expensive proposition. But if the camera is successful, it makes sense to release a M4/3 mount version.

    The bottom line is that the crop is relative to one sensor vs another sensor and not the millimeter size of the lens.

    Someone in the forum has suggested using the S35 sensor as a standard reference when calculating crop factors since that is a traditional filmmakers sensor but the effectual crop factor is going to be the BMD VS whatever sensor size you are accustomed to using.
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