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Thread: 16mm Cine lenses on Micro 4/3 cameras: what crop factors?

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    16mm Cine lenses on Micro 4/3 cameras: what crop factors?

    I am shooting video on GH1 with lenses from old 16mm movie cameras; primarily in C mount, some Arri mount.

    I am trying to determine the FOV of my lenses in 35mm lens equivalent terms, and I'm stumped because of the way different lenses crop/don't crop on the m4/3 sensor.

    Lenses _< 25mm tend to vignette on the sensor. So these don't have a crop factor, right? (or do they have a negative crop factor?) I am seeing more than what the lens was designed to show. So is a 25mm lens then really giving me the FOV of 20mm?

    Lenses > 25mm don't vignette. So 50mm, 75mm, 150mm lenses have full coverage. It is said that the GH1 has a 2x crop factor, but I believe that is for 35mm format glass? These lenses were all designed for regular 16mm or super 16mm format. Yet they are not vignetting like the 25 and below. Still, with m4/3 larger than 16mm format -- does it mean my 50mm lens is giving me the FOV of a longer, 55mm? Or 50mm? or wider? 45mm? 40mm?

    How can one know/measure/ascertain this crucial data??

    Thanks!

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    Senior Member kds315's Avatar
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    Re: 16mm Cine lenses on Micro 4/3 cameras: what crop factors?

    A crop factor is a crop factor is a crop factor....vignetting (or not) has nothing to do with that at all. If a lens covers more than what it was supposed to be (like for 16mm format), just call yourself lucky, it is an optical design side effect. Most retrocfocus designs for 16mm film do not cover much more than needed this is why they usually show heavy vignetting.

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    Re: 16mm Cine lenses on Micro 4/3 cameras: what crop factors?

    Quote Originally Posted by Andreus View Post
    How can one know/measure/ascertain this crucial data??
    Divide by 2. Done. It's based on the sensor size, not on the lens. m4/3 sensor size is just about exactly 1/2 the FOV of the FF (i.e. film).
    -Dragos
    Panasonic GH1/G1, Canon FTb(n)/F-1, Mamiya C330F/RB67 Pro SD, Chamonix 45N-2, Nikon F5 + Assorted Lenses

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    Re: 16mm Cine lenses on Micro 4/3 cameras: what crop factors?

    The so called crop factor is always "2". If you multiply or divide is up to you and from what end you are trying to grasp this. Dragos seem to divide, I never heard anyone else do that...

    Check the focal length, multiply by 2 and you get the focal length you would need to use with a FF camera to achieve approximately the same FOV.

    /Jonas
    Last edited by Jonas; 27th March 2010 at 14:40. Reason: spelling....

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    Re: 16mm Cine lenses on Micro 4/3 cameras: what crop factors?

    Quote Originally Posted by Jonas View Post
    Dragos seem to divide, I never heard anyone else do that...
    It's always a matter of perspective, right? Depends on which direction you come from (and I seem to always come at things from directions different from others ). A crop to me is subtractive in nature, so when I halve the FOV of a FF, it means I divide by 2. Other people look at lens focal lengths, but I try to see things from the perspective of the composition.
    -Dragos
    Panasonic GH1/G1, Canon FTb(n)/F-1, Mamiya C330F/RB67 Pro SD, Chamonix 45N-2, Nikon F5 + Assorted Lenses

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    Re: 16mm Cine lenses on Micro 4/3 cameras: what crop factors?

    Crop factor is the relationship between the size of the sensor and the 36mm x 24mm frame size of 35mm film images. The crop factor for FT and MFT will always be 2x. This allows you to determine that a 50mm lens on a FT/MFT camera will be the equivalent to a 100mm lens on a 'full-frame' or 35mm camera. The reality is a 50mm lens is always a 50mm lens but the angle of view is different as you are taking the image from a smaller sized sensor.

    What is a problem with most c-mount lenses is the cover provided by the lens. Most were not made to cover the same area as a 4/3 sensor, hence the vignetting.

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    Re: 16mm Cine lenses on Micro 4/3 cameras: what crop factors?

    if you are shooting... 35mm cine lenses, there is no crop~factor ... if you are shooting 16mm ... I would guess the crop~factor is about .75...

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    Re: 16mm Cine lenses on Micro 4/3 cameras: what crop factors?

    Quote Originally Posted by Y.B.Hudson III View Post
    if you are shooting... 35mm cine lenses, there is no crop~factor ... if you are shooting 16mm ... I would guess the crop~factor is about .75...
    This statement is as wrong as can be. A crop factor affecting the angle of view has NOTHING to do with the lens type used or its focal length! To reiterate, it is only the size of the actual sensor used as compared to full format 24x36mm

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    Re: 16mm Cine lenses on Micro 4/3 cameras: what crop factors?

    Quote Originally Posted by Y.B.Hudson III View Post
    if you are shooting... 35mm cine lenses, there is no crop~factor ... if you are shooting 16mm ... I would guess the crop~factor is about .75...
    To extend that- if it is 8mm lenses it could be 0.5 to 0.25.

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    Re: 16mm Cine lenses on Micro 4/3 cameras: what crop factors?

    Quote Originally Posted by Andreus View Post
    I am shooting video on GH1 with lenses from old 16mm movie cameras; primarily in C mount, some Arri mount.
    I am trying to determine the FOV of my lenses in 35mm lens equivalent terms, and I'm stumped because of the way different lenses crop/don't crop on the m4/3 sensor.
    (...)
    Andreus; could you please clarify what you mean with "35mm lens equivalent terms".

    Are you thinking of FF lenses as in still photography with a sensor/image window at 24x36mm size, or are you thinking of 35mm film motion picture cameras, and if so exactly what flavour?

    Normally we simply determine the so called crop factor by dividing the diagonal of a FF still camera imagener with the diagonal of the imagener we use. There is no magic about it and it is a simple calculation.

    I think we need to get this thread in order...

    /Jonas

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