For the 35mm f/2 M-mount Zeiss Biogon, the aperture-dependence of the corner color errors ceases at apertures smaller (numerically larger) than f/5.6.
The average and worst case chromaticity errors by f-stop, measured in CIELab Delta-E:
| Avg error | WC error | |
| f/2 | 5.2 | 5.8 |
| f/2.8 | 4.5 | 5.0 |
| f/4 | 3.8 | 5.0 |
| f/5.6 | 2.8 | 3.6 |
| f/8 | 2.8 | 3.6 |
| f/11 | 2.8 | 3.6 |
| f/16 | 2.8 | 3.6 |
The detailed measurements:
f/2:
| UR | LR | LL | UL | |
| L* | -17 | -15 | -14 | -15 |
| a* | 5 | 5 | 4 | 4 |
| b* | -2 | -3 | -4 | -1 |
f/2.8
| UR | LR | LL | UL | |
| L* | -9 | -7 | -6 | -8 |
| a* | 4 | 4 | 3 | 3 |
| b* | -3 | -3 | -4 | -1 |
f/4
| UR | LR | LL | UL | |
| L* | -7 | -6 | -5 | -7 |
| a* | 4 | 3 | 2 | 2 |
| b* | -2 | -4 | -3 | -1 |
f/5.6
| UR | LR | LL | UL | |
| L* | -8 | -6 | -5 | -7 |
| a* | 2 | 2 | 1 | 1 |
| b* | -2 | -3 | -3 | -1 |
Next: what it all means.
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