Lens Reviews Explained
This shows how a rectangular grid is projected by the lens, and therefore how lines will deviate from being rendered as perfectly straight. We also calculate the degree of distortion along both axes of the frame. Again you can select from a range of focal lengths on the lens, but as distortion is essentially independent of aperture, this control is hidden.
The display shows a detailed representation of the lens's distortion pattern (some tests only show you a mathematical curve fit using over-simplified equations). Our data therefore allows you to see any complexity in the distortion, and you can even use screen shots to help find appropriate correction parameters in your preferred image manipulation software.
An additional feature enabled by our collaboration with DxOMark is the distortion graph. This gives some extra information about the degree and complexity of the distortion. For example the graph above shows a complex curve with re-correction towards the corners. This means the distortion will be more difficult to correct in software, and probably require software that uses specific lens profiles to fix it completely.
Along with the grid representation, we present three results in the data panel:
Short edge: defined as the percentage difference in length between the central vertical grid line and the left/right ‘short edge’. Describes the degree of bowing of the upper and lower horizontal lines, which are normally the most distorted.
Long edge: defined as the percentage difference in length between the central horizontal grid line and the top/bottom ‘long edge’. Describes the degree of bowing of the outermost left and right vertical lines.
- Distortion type: Barrel or pincushion
Unchecking the 'Show graphs' box allows you to hide the graph display, and see the distortion grid across the entire frame.