Lens Calibration Testing Process
How we perform a lens calibration.
We often get asked by our customers how we perform calibrations here at our studio location. We understand customers are initially reluctant or hesitant in sending us their expensive equipment (which is why we have instigated probably the most secure and reliable courier collection service in the photographic industry). They are also curious concerned as to how we handle their equipment and what we do. So for the purpose of transparency we thought we would list our
workflow for calibrating a camera / lens combo.
1. Unbox and check camera and lens. We recently applied changes to our health and safety procedures in light of the recent pandemic by using a portable UV wand. This is used to sanitise both the camera and lens. The check consists of ensuring the camera is fully functioning and has a fully charged battery. In addition, we change the camera to the following AF settings which is necessary to carry out the lens calibration. One Shot AF & Single Point & Central focusing (Canon). AF-S & Single Point & Central Point focusing (Nikon).
The lens is checked to ensure the lens's AF can initially be performed, that the OS
(Optical Stabiliser) / VR (Vibration Reduction) is switched off and that any focus limiters are disabled (note these are all reset after the test has been completed).
We also check the front / rear elements and clean if required. If a filter is fitted, we also check on the quality / brand. THIS IS VERY IMPORTANT. We have previously reported on how low-grade / quality filters can severely impact the final captured image. Low quality glass filters can also induce a front / back focusing issue which although this can be compensated for during the calibration process, we cannot however compensate for the loss in resolution that bad glass can induce. If we do find that an unsuitable filter had been fitted, we contact the customer to advise.
2. Securely mount the camera / lens combo onto the test rig and set to the appropriate recommended distance for calibration.
3. Ensure the camera’s in camera calibration feature is enabled (af micro adjustment- Canon, AF Fine Tune – Nikon) and that there are no previous values applied. Please note that is quite common for settings to have either already been applied or in some cases a value applied to all lenses (Canon and Nikon.
4. Attach the USB control cable between the camera and laptop and initiate the calibration software, we then test the USB functionality for the purpose of communication and to undertake the test (any problems with USB connectivity is reported accordingly). In some cases where communication is compromised, we may have to reset the camera settings (this can sometimes be a problem with Canon Eos 7D Mk2’s, 5D Mk IV’s ,1DX Mk 1 & 2’s and certain Nikon models. In this case we will always contact the customer to advise and ask if the reset can be performed. If this is indeed required, we will always perform a camera back up – model specific or communicate with the camera with regards specific camera setup, note and reset to these settings / restore backups at the end of the calibration procedure.
5. Check the focus distance is correct and the test target is properly aligned, properly illuminated and the required test ISO is set.
6. Undertake the calibration test procedure running through thedifferent values from -20 to +20. Once the calculated value has been determined this value is added to the camera’s af micro adjustment menu (Canon) / AF Fine Tune menu (Nikon). In the case of Nikon, the lens is assigned an appropriate number.
7. Screen shots taken of the results and a detailed report saved.
8. Undertake an optional (and chargeable) Lens Optimisation test.
9. Reset camera to previous AF settings / camera back up / camera settings (if applicable).
10. Perform a POST calibration image test. This involves taking a shot (in RAW) of the test target (at the calibration distance), dropping the image into Photoshop and cropping the image to the size of the test target. The image is then enlarged to 200% to inspect text on the bottom of the target. This text is 1/100 th
the size of the test target and is an excellent reference for determining overall sharpness. This is by far the best way to determine the results of the calibration procedure have been successful / made a real-world difference.
11. Perform a final check and sanitise and pack equipment in
bubble wrap before loading
12. Create final calibration report (simplified version) and send out
with test images via WeTransfer.