Hi all,
I would like to know if the focal length varies when recording videos. Because of auto-focus, I believe that for each recorded video the focal length is changing but how much this change can affect 3-D re-projections. Besides, I also don't know if the focal length remain fixed when recording or still it can change.
Please let me know something about that. Thanks.
The GoPro cameras have a fixed wide-angle lens. You can change FoV / focal length of the sensor readout, to some degree. See this field of view table for the Hero3+ Black.
Because GoPro lens parameters, the hyperfocal distance is quite near. The EXIF tags of captured images say~ 0.5m. Since almost everything is in focus, the camera doesn't have to resort to autofocus.
Correspondingly, you don't have to take care of auto-focus issues with these cameras.
Quite. What stays constant per camera regardless of resolution and FOV is the _distortion coefficients_.
The other camera intrinsics will change per FOV/resolution setting. Depending on the parameters you choose cv::fisheye::calibrate and cv::fishey::stereoCalibrate will change your focal length to align left and right views to each other. Also the camera center is dependent on image resolution.
In you case: - Determine distortion coefficients for the widest FOV per camera. - Determine the other intrinsics per FOV/resolution setting, per camera with known distortion - stereo calibrate your each fov/resolution setting - use these happily ever after
Asked: 2016-07-28 05:04:42 -0600
Seen: 767 times
Last updated: Jul 28 '16
