This adapter does not have a lens inside. It only connects a Canon EF or EF-S mount lens to a Fujifilm GFX camera. At the same time, the transfer of EXIF information, electronic aperture control and - most interestingly - autofocus are preserved. Autofocus works reasonably with most lenses tested. There were lenses that had noticeable autofocus problems (eg Canon EF 35mm f2 IS)but they are in the minority.
AF on the Viltrox EF-GFX adapter, I consider it suitable for two reasons:
a) contrast autofocus in cameras Fujifilm GFX 50R / S is already quite slow and, frankly, does not shine against the background of modern cameras. The adapter does not make him worse.
b) for those tasks for which such cameras are purchased, the AF quality of the Viltrox EF-GFX adapter will be sufficient.
Plus, all Viltrox adapters come with firmware updates that can be installed from a computer via a USB cable without docking stations. Firmware often fixes glitches with individual lenses.
The nuances of using full frame optics on a medium format 44mm by 33mm sensor are more related to image quality and coverage of the larger sensor. I've tested quite a few optics.
What are the conclusions and pitfalls?
The good news is that virtually all lenses can deliver sharpness. Expensive full-frame lenses (Carl Zeiss, Canon EF second versions of the L-series) even often completely cover the medium format matrix (only they are already comparable to the native optics).
Image detail on a medium format sensor when using full-frame optics is not always uniform across the entire field of the frame and is not always good at different focusing distances. A safe bet is to shoot everything at f10, then the sharpness will be excellent under any conditions. At apertures up to f5.6, I came across such a situation - when shooting close subjects, sharpness frankly suffered. Focusing at infinity, sharpness was good even at wide apertures.
Full frame mid-range lenses tend to perform worse on medium format than full frame. Nice exceptions: Canon EF 50mm f1.8 STM, Canon EF 40mm f2.8 STM and Sigma 70mm f2.8 Macro. These penny lenses easily cover the medium format sensor and deliver a very high level of detail. By the way, all macro lenses I tested (4 pieces) covered medium format. But the portrait photographers had good coverage when focusing at close distances (which is enough for portraits), but gave a noticeable vignetting at infinity.
In general, on a "small" medium format 44mm by 33mm CAN use full-frame optics. The question is - why and why? Why - the answer is obvious, in order to save money and not buy expensive native optics. What for? To adapt the existing fleet of optics and get a wider range of focal lengths. Everything seems to be the same, though there are many "but«.
It is possible to justify the use of adapters on crop cameras when it comes to both amateur use of technology and small budgets for updating technology. With the medium format, the paradigm of the whole event changes somewhat. Typically this technique is taken to maximize. Medium format with native optics (I've tested various Fujifilm GFX lenses) gives you an evenly sharp image without aberration, drop in sharpness in corners, without distortion and without all those nuances that we often close our eyes to when shooting at crop or full frame. From the point of view of the perception of photography as it is, these subtleties are not so important - if you look globally. But from the perspective of a person who pays a lot of money for an IDEAL, the medium format makes sense. The image is so high-quality and optically verified (I find it difficult to find the right words) that it is not enough to consider it at 100% approximation, it is better to do this at 200-300% in order to see all the details and enjoy the ideal. This is a very specific activity, I must tell you. But this is exactly the idea of using the medium format - no compromises.
The full-frame optics on the SF behave well. It upsets when it turns out to be worse than in the full frame - it lathers around the edges, then aberrations and other nasty things appear on the open ones. You can shoot at f10 and you can pick up the right lenses that will be suitable for certain tasks in medium format. This just begs the question, why not continue to shoot in full frame, if you are willing to put up - albeit with small - but compromises?
Medium is not about economy and adapters. This is about the maximum at any cost. VIP segment, so to speak. If we draw a parallel with cars, then shoot through the adapter on the SF, it's like putting Volkswagen wheels on Lamborgini. The car will drive (VW makes good wheels and cars too), but Lamborgini will not reveal its potential.
Personally for me was interesting ultra-wide angle on medium format. The Sigma 14-24mm f4 ART and other good full-frame widths can cover medium format, but only selectively at some focal lengths. At the same time, I remember the picture on the Fujinon GFX 23mm f4. Full-frame lenses (even those with good sharpness) do not produce such uniformity in images. In one word, I can describe this feeling precisely “uniformity". But in the full frame the same Sigma 12-24mm f4 ART - a very, very decent lens. He reveals himself much better in the full frame.
Watch my video tests with the Viltrox EF-GFX adapter:
Also read my article “Do you need medium format?«
By the way, Metabones has released an adapter EF-GFX Smart Expander.