2013-06-30

Chinese 25mm f1.4 and 35mm f1.7 CCTV Lenses für Micro Four Thirds



    I found these 2 chinese lenses for $18 and $38 and wanted to give them a try.


    • C-Mount 50mm f1.4 covering a 2/3" sensor
    • C-Mount 35mm f1.7 covering a 2/3" sensor
    I'm trying to evaliate their usefulness for FullHD video recording and for 5MPx photography.
    Since they are f1.4 and f1.7, I'm comparing them to a completely unfair competition of modern high end lenses with similar apertures.



    • Panasonic/Leica 25mm f1.4
    • Voightländer 25mm f0.95
    • Voightländer 17.5mm f0.95
    My camera is a Panasonic GH2 (with hacked firmware but that doesn't change the results here).
    EX-Tele mod is not used. Aspect ratio is 16:9 . Thus the crop factor is 1.86 since it's a multi-aspect sensor and no regular  4/3 sensor.

    A normal 4/3 sensor would have 2.0 and a 16mm Blackmagic Pocket Cinema Camera 3.0 .
    These would have less of an issue with the blurry corners of these lenses made for 2/3" or 1"=3/3" sensors. We are using these lenses way outside their intended sensor size.
    • All Photos (Including other apertures. Scaled to FullHD due to Picasa quota.)

    Here are the references:
    Leica 25mm Voightländer 25mm Voightländer 17.5mm
    (All wide open at the fastest aperture)

    Panasonic/Leica 25mm f1.4

    Voightländer 25mm f0.95

    Voightländer 17.5mm f095

    Now the C-Mount 50mm wide open and fully closed.
    I know they are hard to compare since the focal lengthes put the C-Mount lenses at a disadvantage.
    On the other hand trees are known to have tons of detail at any field of view.
    C-Mount 25mm f1.4Add caption

    C-Mount 25mm f1.4 at >f10
    These photos have been scaled down to 1920x1080 FullHD since the lenses are completely unusable beyond that.
    Both lenses are extremely prone to stray light. So don't judge the contrast using these images.
    They must be used with a lens hood (no thread, must be improvised) or french flags.
    The center of the f1.4 image is somewhat usable if moving. Everything outside the center is so blurred that this only works out when it's
    • either a dream sequence or 
    • something in the center of the frame is to be shown in a very shallow depth of field anyway or
    • it's an action cam that's only visible for a short period with the viewer distracted by the action and the lens is at risk of being destroyed.
    Stopped down it gets somewhat better but why would you use this lens stopped down except to get lots of motion blur in an action sequence.

    Now the 35mm f1.7 C-Mount:

    C-Mount 35mm f1.7

     
    C-Mount 35mm f1.7 at >f10

    Same issues. Just another focal distance.
    These may yield slightly better results on a Blackmagic Pocket Cinema Camera due to the higher crop factor yet they still will be very blury outside the center.

    Both are nice toys where it's not important if they break or not since they cost next to nothing.
    For a few Euro extra you'll get some old Canon FD glass that may have purple fringing and just match the sharpness of these in the center but keep that sharpness into the edges.
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