Nikon Z8 400% Zoom Manual Focus vs. Autofocus Accuracy

Nikon’s Z8 version 3.0 firmware adds the capability to zoom the viewfinder to 400%. I wanted to see if this level of zooming during manual focus could allow even more accurate focus than autofocus.

The most accurate focus that I have tried on my Z8 so far is the “Pinpoint” AF, which is only available in AF-S mode. It’s only a hair better than using 3D focus in AF-C mode, so I rarely bother with Pinpoint focus. For routine day-to-day focus, I much prefer AF-C with 3D focus and the practicality of AF-C over AF-S. What follows is a study comparing those 3 kinds of focus modes.

Manual focus practicality and ease of use heavily depends upon the focus ring range of rotation. Lenses with 180 degrees and less of total focus ring rotation range are quite difficult to get critical focus, especially while hand-held.

I used my Sigma 70-200 f/2.8 Sport lens in these tests, zoomed to 120mm at f/2.8.  Its focus ring rotation range is about 135 degrees, which is fairly typical of AF lenses. The 400% viewfinder zoom was quite challenging to focus; I kept overshooting the best focus slightly. This is a good problem to have, however; the viewfinder made it easy to see how focus changed with even the slightest focus ring rotation.

To get the best analysis of focus accuracy, I will use the MTFMapper program. It is far more picky than human vision to discern what’s in focus, via its resolution measurements of a test chart.

The Fn2 button assigned 400% zoom

Full LCD display

400% display zoom is pretty extreme

I set up the camera on a tripod and used a wired remote for all of the photographs to rid vibrations. I took 10 shots each with AF-S/Pinpoint, AF-C/3D, and manual focus with 400% zoom. I de-focused between each test shot to guarantee a full re-focus each time.

I assigned the viewfinder zoom feature in the Custom Controls menu to the Fn2 button. The new addition to the version 3.0 firmware is to go beyond 200% all the way to 400% zoom. While using autofocus, the zoom is automatically centered on the current focus point position.

One of the AF-S, Pinpoint shots of my resolution chart got messed up when I accidentally tugged on the wired remote. Since the resulting resolution measurement on that shot was terrible, I omitted that shot from the data that follows.

Sample resolution measurement using AF-S, Pinpoint

AF-S, Pinpoint test chart with overlaid measurements

Sample resolution measurement using AF-C, 3D

AF-C, 3D test chart with overlaid measurements

Resolution measurement using manual focus, 400% zoom

Manual focus, 400% zoom chart with overlaid measurements

Each resolution measurement

Resolution data plot

If you don’t notice much resolution change from one type of focus method to another, neither do I. That’s a good thing. It means that manually focusing can get just as good of results as autofocus, as long as you use the viewfinder zoom to analyze critical focus.

I decided long ago that focus-peaking wasn’t quite accurate enough for critical manual focus; you could only get approximate focus. By combining focus peaking and the zoom feature, you can be confident that your manual-focus shots will be sharp. Focus peaking is still an excellent way to rapidly get ‘close’ to correct focus.

With the Fn2 button assigned to the viewfinder zoom, it’s simple and fast to press it and toggle between the ‘normal’ and ‘zoomed’ view. Sometimes, 400% seemed a bit extreme when compared to 200% zoom. Since it’s programmable, it’s great to be able to change your mind whenever you want.