# focal length fx and fy , do they change for a camera capable of zooming ?

Hii I am using a logitech PTZ camera . i am trying to find the intrinsic camera matrix from opencv . Do the fx and fy values change when calibrated differently ?? Or are they constant ?

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no, fx and fy are not constant, they depend on the zoom state of your camera.

so, whenever you change the zoom ( manually or by autofocus ), you need to recalibrate to get the current intrinsic matrix.

with a bit of luck, you can toggle the autofocus from the settings panel , try:

VideoCapture cap(0);
cap.set(CAP_PROP_SETTINGS,1);

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Are fx and fy not the physical focal length values ?? If they are then fx and fy have to be constant right ??

( 2013-06-12 05:30:47 -0600 )edit

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