FoCal’s MultiTest takes a whole set of measurements across the aperture and focus range, letting you analyse various aspects of the camera and lens performance.
One particular aspect that has some relevant to mirrorless cameras and AF Fine-tune is focus shift across the aperture range, and picking an AF Fine-tune value that gives you the best results within a range of apertures.
AF-S Nikkor 50mm f/1.4G
Taking a look first at an F-mount lens on the FTZ adapter, the chart below shows the line of best focus as you change the aperture. Along the bottom is the aperture value, and along the side is the AF Fine-tune value. The colour of the grid indicates quality, with red being poor and green being good. The diamonds show the AF Fine-tune required for the best quality at each aperture.
Notice how at no aperture does an AF Fine-tune of 0 (i.e. no calibration) give you the best quality. If you were to calibrate for the best wide-open performance, you’d use an AF Fine-tune value of around -3.
MultiTest uses all the data to build an Aperture Sharpness profile which shows the difference between uncalibrated and calibrated performance (for best wide-open quality), as well as the quality if you were to manually focus. The Peak ARQS shows you the quality if you pick a calibration value that is designed to give the best average quality across the whole aperture range.
Notice how from f/2.2 through to around f/8 that there is a significant difference between the quality when calibrated (the green line), and when not calibrated (the red line).
Nikkor 24-70mm f/4 S
Looking at a decent quality Z-mount lens, it’s clear to see that calibration is less necessary for wide-open performance, but there is still some focus shift as the lens stops down. With a slower lens like this f/4 example, the focus shift will have less impact as the depth of field increases so much at the point the focus shift becomes larger (e.g. from f/9) that the quality loss will be negligible.
But if you mostly shoot wide open, there is a little bit of sharpness to be gained by calibrating. Again, see the difference in quality value between the red (uncalibrated) and green (calibrated) lines below – there’s a small quality improvement to be until around f/7.1.
Like with the Stabilisation Test, we captured a limited amount of data from the Z9, but the MultiTest results do clearly show a benefit to calibration – more so on the adapted lens in this example, but still squeezing out every little bit of performance even from native Z-mount lenses.
Thanks for reading!
We hope you’ve enjoyed this overview of the Nikon Z9, the photos and information from our play time at Durdle Door and the analysis results.
We’d love to hear your thoughts in the comments section below!