Calibrate a lens before measuring a horizon
Photograph straight references with fixed lens settings, then compare their recorded curvature at several positions in the frame.
What you need
- Camera and stable straight-line target
- Tripod and fixed focus/focal length
- Original files and a level reference
Collect the readings
- Photograph a grid or several truly straight lines spanning the frame. Hold focal length, focus and any in-camera geometric correction fixed. Record those settings with the original file.
- Place the same reference near the centre and near each edge. A line through the optical centre can appear straight even when offset lines bend strongly.
- Use the horizon projection tool with the entered pitch and field of view to compare rectilinear, equidistant and equisolid families. The plot is a model comparison, not a fitted calibration of your camera.
- When photographing a horizon, measure camera pitch independently. Keep any corrected image beside its original and identify the transformation; cropping alone can hide where the optical centre was.
Compare the predictions
Projection family, optical centre and pitch affect the line together.
A nominal focal length alone does not specify every distortion coefficient.
A known reference distinguishes lens bending from unknown scene geometry.
Open the related calculation →