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Summary: Genlocking of Video Cameras

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  • Summary: Genlocking of Video Cameras

    Dear Biomch-L Readers,

    Thank you to those who replied to the question on genlocking of video
    cameras. As promised here the summary of replies.

    **************** Original Posting *********************************

    I have two Panasonic AG-DP800HE video cameras which I am wishing to
    genlock. Thus far, the only solution I have come up with through
    talking to the television/video technical people is to input a black
    burst signal from a master source (such as a signal pulse generator)
    to both cameras and then adjust the timing of one camera relative to
    the other. Apparently, this may require the use of either a monitor
    and/or mixer. Is there any other way to do this?

    Thank you for your time and I will post a listing of all replies.


    Angus Burnett
    Sports Biomechanist
    Western Australian Institute of Sport c/- Superdrome
    P.O Box 139
    Claremont, Western Australia, 6010
    E-mail: Ph: +61 9 387 8166 Fax: +61 9 383

    ***************** Replies ****************************************

    (1) I have been through the same process talking to video technicians.
    However, finally I found out, that genlock actually means to feed the
    video signal of a master camera to a number of slave cameras. My
    impression is that the genlock signal is not a special signal, it is
    the whole video signal.

    The slave camera should be set up as a slave - normally this is
    performed in a sort of menu system built into the camera. As far as I
    know you cannot genlock two camcorders, but you can use one camcorder
    as a master and then genlock several slaves to it.

    You can buy special devices to split a genlock signal, but to our
    experience you may simply use a BNC T-connector on the genlock input
    of each camera.

    Our technical staff constructed a small very simple device, which
    takes 4 video signals as input and outputs one signal. This signal is
    a mixture of the four inputs, i.e. when you display it on a monitor
    you will see four pictures on top of each other, BUT the important
    thing is that if the four cameras are not genlocked the picture will
    tilt and you will see nothing, so this is a convenient test that your
    genlock works.


    Erik Simonsen


    (2) I have carried out 3D studies using the setup described below,
    where the cameras were genlocked using a Panasonic device. I hope info

    '......For 3D analysis at least 2 frame locked (using Genlock adapter
    Panasonic WV-AD36E) cameras (Panasonic F15) must record the motion. An
    electronic time code and video field number were burnt onto each field
    by the genlock/video audio amplifier (model: VM10R)........'

    yours sincerely

    David Davis


    (3) I'm not familiar with your cameras but from your comments, I
    suspect that they have a "gen-lock" input. If this is the case, then
    any video signal will lock them. Typically, in a studio, a
    "black-Burst" signal is used, as a main sync, but you can use one of
    the cameras as a master and send its signal to the second camera as a
    slave. Beware that video signals cannot be terminated more than once
    by 75 ohms, so you will need a video distributor ie a buffer
    amplifier, or make sure that the slave camera gen-lock input is high
    impedance. Some National cameras have a small switch for this

    As for set-up: In a studio it is necessary to ensure that the signals
    applied to the vision mixer are exactly in step, both vertically and
    horizontally. Adjustments on the camera are supplied for this
    purpose. These make up for time delays in the connecting cables.

    If you are using the cameras for movement analysis in eg a PEAK
    system, then only vertical sync is required, to make sure that the
    shutter operates at the same time in each camera. Since the delays in
    the cables and circuits are of the order of less than 64 uS, one TV
    line, 1/312 of a frame, or 1/15625 Seconds, the error in shutter
    timing is quite small. The effect is that the shutter will "open"
    perhaps 1/15625 S later on the slave camera. This is small compared
    to the possible 1/1000 S shutter speed.
    The error would show up as an different position of a point in the
    slave camera as compared to the master. The error will obviously
    increase as the shutter speed increases.

    To accurately set up the gen lock, you could use a dual trace CRO and
    observe the two video signals. adjust the Vertical gen-lock so that
    the vertical sync of the two signals line up. It may be that there
    isn't a vertical control.

    There are digital vision mixers that internally synchronize the
    in-coming video. The problem here is that there is a delay in the
    digital processing and it is not possible to know when the shutters
    opened without some visible marker eg a spinning disc on a 50Hz.

    John Yelland

    .................................................. ..................
    Technical Services Unit, Faculty of Health Sciences, Carlton Campus,
    Latrobe University, Melbourne, Australia.
    Tel. (03)285 5332 Fax. (03) 285 5111 | Locked Bag 12
    John Yelland : | Carlton South P.O.
    | Victoria 3053

    "The cutting edge of high technology
    is hand-made and polished by artisans". c 1995, John Yelland
    .................................................. ...................


    (4) With the Panasonic cameras I have I am able to gen-lock an AG455
    camcorder as the master to a F15. A cable takes a signal from the
    'video out' on the camcorder and is input into the 'gen-lock' socket
    on a WV-AD36E gen-lock adapter on the F15. I hope something like this
    can help with your type of Panasonic cameras.

    Best regards

    Mr D.R.Mullineaux
    School of Social Sciences
    University of Teesside
    TS1 3BA

    Tel: +44-1642-342355
    Fax: +44-1642-342067


    (5) We use Pelco VSS100DT Video Screen Splitter/Inserter and Vidotek
    VDA-16 Video Distribution Amplifier to genlock two Panasonic WV-CL350
    color video camera since 1991. There may be newer models now.


    (6) No. I used two Panasonics and sychronised them using a custom made
    Genlock box. You use one camera to drive the other via the genlock
    circuitry. Very easy if you have the box already made up for you. If
    you have not I think you can buy one. They are not too costly I think.
    I used one my supervisor had, so I do not know exactly how much they
    cost to buy new.

    Best wishes,

    Julian Tang MA PhD MB BS