A lensfun profile is scaled by the crop factor of the recorded frame. `lookup` took the body's from the
database whenever the camera was in it, so a full-frame body shooting a crop of its sensor (APS-C /
Super 35 mode, or switched there by an APS-C lens) had the profile applied as if the crop were the full
frame: the crop's corners got the full frame's corner distortion and vignetting. On a Sony ILCE-1M2 in
APS-C mode with the FE 100-400mm F4.5-5.6 GM OSS at 400 mm, the warp's r³ coefficient was the full
frame's 0.0215 instead of 0.0096.
The 35 mm equivalent focal length shows the crop: when it implies a crop factor more than 10 % above the
body's, that wins (`frame_crop_factor`); within 10 % the difference is the tag's whole-millimetre
rounding and the body's value stands. Without the body in the database the 35 mm equivalent is used, as
before.
Tests: `in_camera_crop_mode_uses_the_frames_crop_factor` (fails on main: in its profile the APS-C frame's
vignetting gain is 0.40 instead of 0.18) covers APS-C mode, full frame, a 35 mm equivalent rounded by a
millimetre, no body in the database and a hostile focal length. Checked on 19 private ILCE-1M2 ARWs
(FE 100-400mm GM, Sigma 24-70mm F2.8 DG DN | Art, full frame and APS-C, firmware 2.01-4.00): every
APS-C coefficient is the full-frame one scaled by 1/1.5².
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Profiles are interpolated in focal length (vignetting also in aperture and
focus distance), scaled by crop factor, and converted by least squares to the
DNG WarpRectilinear / FixVignetteRadial polynomials the pipeline already
applies. The lensfun database (CC-BY-SA) is only read from a directory the
user supplies; nothing is bundled.
Sources: lensfun's published database format and lens calibration
documentation (no lensfun code read), PanoTools wiki (a, b, c distortion
model), DNG specification 1.6 (WarpRectilinear, FixVignetteRadial);
interpolation and fitting: own design.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
