This is the 39th in a series of posts on the Fujifilm GFX-50S. The series starts here.
I’m not sure where to go with the focusing studies on the GFX. Maybe it’s time to gather my thoughts and tell you all what I think I’ve discovered. I’ll cover manual focusing first, then autofocusing.
Manual focus
The controls for the GFX focus magnification are ergonomically excellent. Press the back thumb wheel to enter magnified view, and spin it to change magnification. Unfortunately, the maximum magnification is not enough for critical focusing. That means that you have to use peaking. Peaking seems to have a bad name because it’s such a blunt instrument when you’re looking at the full image, but as the magnification goes up, it becomes more and more useful. However, with the GFX you only have two peaking sensitivities available (not counting off), and that’s not enough. With a sharp lens and a high-contrast target, even at maximum magnification, setting the peaking to low will still light up the finder too much when the image is close to being in focus. With mechanically-focused lenses, you can find one side of sharp and then the other side, and split the difference. That doesn’t work with focus-by wire lenses, since a given amount of twist of the focusing ring translates to different amounts of lens element motion depending on how fast and how far you move the ring.
All the things above conspire to make critical manual focusing fairly good (but far from great) with adapted helicoid lenses and barely acceptable with the native focus by wire lenses. I’d put the focusing with adapted lenses about the same as the D810 (that only applies if you turn peaking on in the GFX, though — the D810 doesn’t have peaking). With the two native lenses I’ve tried — the 63 and 120 macro — the focusing experience is better than the D800, but short of the D810. In no case does the GFX provide manual focusing that’s the equal of the a7R, or even the a7RII. The standard of focusing tolerance is not the same across those cameras, since the GFX is capable of so much greater sharpness when the image is in focus; I’m being harder on the GFX because it can do so much more, and thus the consequences of a small focusing error are greater. Here is a focusing strategy that works well with the GFX.
The best strategy for manually focusing the 63 mm f/2.8 lens is to focus wide open. That doesn’t work with the 120. The best way to deal with the 120 macro is to focus at taking aperture, or maybe slightly open from there.
Autofocus
With both native lenses, autofocus works will wide open. It also works well stopped down a fair amount. But, with some subjects, it gives inconsistent and inaccurate results at f/4 and f/5.6 with the 63 mm lens, and at f/5.6 with the 120 macro. If you know that, you can work around the issue.
Since f/8 on the GFX is about like f/5.6 on a full frame camera for diffraction and depth of field, stopping down that far is not much of a privation, and you can always use both lenses wide open if you want to blur the heck out of the background.
By the way, I don’t find the GFX MF/AF mode that useful. If you’ve enabled it, you can autofocus the lens, then twist the focusing ring. That immediately gets you magnified view, and you can tweak the focus. However, you can’t get back to viewing the full frame without losing your focus point. Or at least I can’t figure out how to do it. It’s probably something involving back-button focusing. I’ll play with it some more.
Let me put this in perspective. There are many uses for the GFX — perhaps the majority of them — for which the present autofocus performance is just fine. This autofocus issue is only important if you’re trying to get the most of the great sensor and the sharp natives lenses. I think this situation is a little like the a7R shutter shock. There are many people who said that the effect didn’t exist. They said that because they thought their pictures looked just fine to them. There will be many GFX users who feel the same way about the autofocusing on their cameras. As a proportion of the user population, the satisfied GFX users may be even higher, since the absolute level of performance is so high.
Is auto focus performed wide open by default or is the default the selected aperture? Thanks for your great testing program.
Phil Lindsay
I can’t tell for sure. In the case of the 120, it produces results that you couldn’t get focusing wide open, so it must be stopping down. The defaut for manual focus is wide open but you can stop the lens down before focusing.
Fuji Tech Support confirms that AF is performed at the shooting aperture by default and that the only way to AF wide open is to set the lens to the wide open aperture. They said that setting the shooting aperature by using the aperture ring on the lens or setting the lens to “C” and adjusting the camera thumb to the desired aperture has the same functionality with respect to always performing AF at the shooting aprature. How do Nikon and Canon handled AF?
Thanks
Phil Lindsay
Every SLR I’ve owned has focused ith the lens wide open, but the aperture used by the phase detection system is less than that for fast lenses. When lenses reach narrow maximum openings, PDAF usually ceases to work at all.
Hopefully Fuji will listen to its users.
1. Change available magnifications, or add more including 100%, or make them adjustable.
2. More or adjustable focus peaking levels
Seems that both might be acomplished in firmware updates.
Does shooting tethered make any difference in what is available to help in manuall focusing?
Could it offer more than just what is available on the camera alone?
Shooting tethered with a big screen makes everything bigger, which helps. I have shot other cameras tethered to a Atomos display, and used the peaking in the display, and that works.