Hi everyone,
I’m working on a setup with my Canon CRN700 tracked using free-d, and I’ve calibrated the camera using the basic calibrator. I’m a bit stuck on one aspect of the process.
My goal is that when autofocus is activated during close-up shots, the background also gets appropriately blurred. To achieve this, I attempted to enter the compound tracked camera, set the input %N=1, and within Line %N, I extracted the focus sensor data. I then used a unlerp node between 0 and 100, connected it to a copy scalar, and finally routed it to the focus pin of the output. However, the values don’t seem to match the actual performance of the camera.
Could someone explain the correct procedure or adjustments needed to align the sensor values with the real camera behavior? Any insights or suggestions would be greatly appreciated.
Thanks in advance!
Hi,
The sensor pins, such as the Focus Sensor pin, provide raw, uncalibrated data, whereas the Focus Distance pin provides the calibrated values. If Canon CRN700 doesn't provide a calibrated focus, you need to create focus calibration using the Basic Calibrator.
This process is explained in the first part of the first comment in the following post: https://my.aximmetry.com/post/3383-ue-tracked-camera-focus-distance-with-pt
For more information on the Basic Calibrator and Focus calibration, see here: https://aximmetry.com/learn/virtual-production-workflow/preparation-of-the-production-environment-phase-i/tracking/basic-calibrator/.
Note that the calibration files from the Camera Calibrator (Lens and Tracking calibration) can be used in the Basic Calibrator, so you only need to perform the focus calibration with the Basic Calibrator. After you've created the focus calibration, the camera compound in Aximmetry will automatically set the focus of the virtual camera, so you won't need to edit the camera compound.
If you really want to create the focus calibration within Aximmetry using the Unlerp module, you'll first need to measure the maximum and minimum values provided by the Focus Sensor pin. Set these values as 'A' and 'B' in the Unlerp module, instead of using the default 0 and 100. However, this approach will only result in a linear interpolation between the maximum and minimum focus values, while the Focus Sensor value is unlikely to be linear when calibrated to Focus Distance (meters). You could use the Curve module with multiple keys for different measurement points and different interpolations, but this will still only be accurate for a single zoom level.
Ultimately, this is similar to what you'd do with the Camera Calibrator, so it is advisable to use the Camera Calibrator for its ease of use and to obtain accurate results.
Warmest regards,