Quality of Focus – Focus Consistency
(See Chart Features for general chart features - changing scales, copying to clipboard etc)
The Image Motion chart shows how the image of the FoCal target moves across the image sensor as the test is run.
Key:
- Green circles - image motion (in pixels) for individual shot
- Green area - the range of motion for all shots at each aperture
Where FoCal Comparison Data is available, the horizontal coloured bands indicate how this lens compares to other lenses of the same type on the same camera model:
- Green area - above average performance
- Blue area - average performance
- Red area - below average performance
Basic Interpretation
As the lens is defocused and refocused, the image projected onto the sensor can move slightly. A high-quality lens in good condition should not exhibit large amounts of movement, so this chart can be useful to detect any issues related to focus operation.
The Image Motion chart shows the absolute number of pixels moved for each image compared to the first image captured. This metric does not include a direction - simply the overall number of pixels the image has moved.
Typically, the Image Motion should be significantly less than 10 pixels, and a repeatable higher value could indicate misaligned lens optics, camera movement or vibration during the test or other environmental or lens issues.
The example above shows a good quality result, with no discernible movement across the test.
Further Details
FoCal Comparison Data Interpretation
The horizontal red, blue and green bands of the FoCal Comparison Data allow you to see how your lens is performing compared to the average values of other users of the same camera/lens combination.
The example above shows a lens showing no movement of the image between shots, and the results are sitting in the very small green area at the bottom of the chart showing this lens is performing better than the majority of other lenses on the same camera.
Red-Blue Ratio – Focus Consistency | This Page | Dual Pixel Raw Focus Offset – Focus Consistency