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Aburnett
09-11-1996, 11:19 AM
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.

Regards,


Angus Burnett
Sports Biomechanist
Western Australian Institute of Sport c/- Superdrome
P.O Box 139
Claremont, Western Australia, 6010
E-mail: aburnett@wais.bekkers.com.au Ph: +61 9 387 8166 Fax: +61 9 383
7344


***************** 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.

Sincerely


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
helps.

'......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
purpose.

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.
motor.

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 : j.yelland@latrobe.edu.au | 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
David

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

Tel: +44-1642-342355
Fax: +44-1642-342067
Email: D.R.Mullineaux@tees.ac.uk

***************************

(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.

lichunwu@pioneer.arc.nasa.gov

***************************

(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