Focus calibration
After Splicer has been moved, transported, or the lens has been changed, the focus system must be recalibrated to maintain precise alignment between the Y axis (object distance) and the V axis (sensor-to-lens distance). This recalibration ensures that samples remain sharp across the full range of motion and that future captures can be automated with reliable focus parameters.
The calibration process begins by capturing a series of line scans of a focus calibration target placed at defined distances along the Y axis. Typically, the procedure starts at Y = 100 mm and continues in 50 mm increments up to 500 mm, followed by 100 mm steps until the Y axis limit at 1100 mm is reached. Each scan involves movement only along the X axis, with the V axis (focus) kept fixed for the duration of a single capture. A GCODE file for linear movement can be found on Github. During Focus Calibration, the Line Sync Source on the Frame Grabber needs to be switched to internal line triggering. See Chapter Frame Grabber Settings for detailed information.
The resulting images are examined to locate the region of maximum sharpness, indicating where the image plane intersects the physical target. According on whether the sharp region appears in front of or behind the target's expected position, the V axis is adjusted manually, and a new capture is acquired. This iterative process is repeated for each Y axis distance until each optimal V (focus) value is identified.
Once a full dataset of Y and corresponding V values has been established, the relationship can be modeled using a polynomial curve function. Surprisingly, ChatGPT has proven to be an effective tool for estimating the curve from raw calibration data. The resulting function allows Splicer to calculate the appropriate V value dynamically for any Y position.
As a last step, the function is to be embedded directly into the Splicer Animator Script, enabling all future GCODE exports to include automated focus compensation without requiring manual adjustment. The calibration target used in this process is open-source and can be downloaded and 3D-printed from the official GitHub repository.
SPLICER / FOCUS VALIDATION, 17. Februar 2025
C-print, 30x37.5cm on paper 40x50
This image is a validation capture of Splicer’s autofocus calibration.
From left to right are a sequence of Y-axis positions, each
corresponding to a different object distance from the lens. The photograph
reveals how the sharpness plane shifts across the distance: at times
falling in front of, and at other times behind, the calibration target’s
ideal focus point. The work functions both as a diagnostic image and
a representation of the spatial and optical interplay.