This is the 12th post in a series of Nikon D850 tests. The series starts here.
The D850 has a tuning feature for the phase detection autofocus (PDAF). For the contrast detection autofocus (CDAF) no tuning is necessary or possible. The PDAF tuning works like this:
- Manually focus on a target at your chosen aperture and distance.
- Tell the camera to autofocus on that target, then recommend a correction
- Store the correction in memory for that lens (this is done automatically)
I’ve had a D5 since they first shipped, and thus I have experience with a similar system. Sounds neat, right? Nobody likes to tune the autofocus manually, and many don’t bother. But Nikon recommends that you don’t use the feature unless you’re having problems. Why is that?
It turns out that there are two sets of random variations that can cause all kinds of trouble.
- Errors in manual focusing — your errors
- Errors in autofocusing, which the camera needs to do to estimate the correction — camera errors
The combination of the two sets of errors means that you need to perform the procedure many times and average the readings for best results. If you do the auto-tune just once or twice, you are likely to make things worse, not better. I believe that’s what Nikon wrote their cautionary note.
Let’s talk a bit about the errors in turn.
The D850 is easier to focus manually than its predecessors, the D800 (which was awful), and the D810 (which wasn’t bad). In any of the three cameras, you need to use live view to focus critically; using the viewfinder is at best approximate, especially since all the focusing aids have been removed in the transition from manual-focus-only film cameras to autofocus-primarily digital ones. I for one am very sad to have experienced the demise of by far the most accurate reflex focusing aid, the aerial image ground glass. For those too young to remember, in the olden days when dinosaurs roamed the earth, SLRs had interchangeable ground glass finder inserts, and one of the options had a clear center with a very fine cross embedded in it. You got the image approximately in focus with the ground glass on the periphery, then moved your eye up and down or from side to side. If the image was out of focus in one direction, it moved one way with respect to the center of the cross. If it was OOF the other way, it moved the other way. RIP, aerial focusing. It was great, even though it only worked on-axis and was slow at best.
But I digress. Where was I? Oh, that’s right: liveview. The D800 was immensely handicapped by line skipping sensor readout. The D810 improved that. Neither offered focus peaking. The D850 has still better liveview clarity, and adds peaking. What’s not to like? Two things:
- The magnification doesn’t go high enough
- The peaking is too weak when used at full magnification.
Insufficient live view magnification is a common complaint. I don’t think I’ve ever heard anyone say their camera had too much magnification for critical focusing. Too-weak peaking is not a problem I’ve ever had with a camera; most have peaking that’s too sensitive. But even with the peaking set to its most-sensitive position on the D850, with the finder zoomed in all the way on a Siemens Star with a sharp lens like the 105/1.4, I can’t get the peaking to light up. It looks like Nikon tuned the peaking for low-magnification use. So, on balance, I find that I can’t manually focus the D850 as consistently as either the a7RII or the GFX-50S. Both of those cameras have their manual focussing issues, but I’ve found ways to get good results from them. It’s kind of strange that the D850, with a better LCD display at magnification than either camera, doesn’t deliver the godds as well. And of course the D850 can’t be focused through the finder at all in live view, which is the best way to use both the GFX and the a7RII.
Oh, and don’t be tempted to use the misfocusing arrows in the D850 finder when you’re dong the manual focusing part of auto-tune. They are driven by the same information that drives the PDAF itself.
Now we get to the variations in PD autofocus. In the D850, they are profound:
There has to be a better way to set up your PDAF than running endless variations of Nikon’s auto-tune procedure. I have some ideas, and I’ll get to them in a future post.