Adapting GFX: The Introduction of 35mm “Full Frame” Lenses on the GFX

As I have alluded to in a burst of recent posts, I am planning to generate a small database of lenses for use on the Fujifilm GFX series. Here’s my chance for an introduction to give my rationale and to lay the foundation of this endeavor. I’d like to break this down into three “Y’s.”

Let’s begin with a personal “why”: I’m choosing to use Sigma lenses to obtain focal lengths and apertures not currently offered in the GF lens lineup. Fujifilm’s lineup is sparse at best, and apertures wider than ƒ/2 aren’t represented. It’s not that I’m a bokeh whore; it’s that I need more light gathering for astrophotography and Fujifilm’s widest lens, a 23mm, has a maximum aperture of ƒ/4 and that’s just not going to work without a star tracker due to the sensor’s 51MP resolution. I’m hoping to print a few of these so what counts for “sharp” on the web doesn’t work at 20″ print sizes. Other benefits: 35mm lenses are much cheaper, especially used, and SLR lenses usually have direct focusing helicoids unlike the “drive by wire” systems seen on most mirrorless lenses. The GFX system just isn’t mature enough to have grown both a complete lens lineup or a diverse used lens market.

Now for “why” I’m choosing Sigma lenses with Canon EF mount: Sigma’s Art primes have been getting stellar reviews for their more strategic compromises. They’re no longer just great for the price; they’re simply great. Sigma has designed their Art lenses to cover a larger imaging circle; this increases the area of the sharpest part of the lens, the center. This larger projected imaging circle means a better chance of covering most of, if not the whole sensor, and reduce the need to use the built-in “35mm Crop Mode.” While handy, it does reduce output from 51.4MP to 31MP. Instead, should any hard vignetting occur, I would prefer to use a small crop from 4:3 to 5:4, or even 3:2, cutting away the affected corners and maintain 45+MP for further adjustment of the composition without greatly compromising the ability to print large. Finally, Sigma has stated that all of their Art series lenses were designed to resolve at least 50MP for use with high resolution cameras like the Canon 5DSR, Leica SL2, Nikon D810, D850 and Z 7, Panasonic S1R, Sony α7R series, and Sigma’s own SD1 Merrill. Therefore, the lenses should be able to resolve details just fine, at least in the center, on the GFX 50S and 50R’s 51.4 megapixel sensors.

As for the choice of Canon EF mount, at 54mm it has a wider inner diameter than Nikon’s F mount, which offers benefits like wider maximum apertures and less aberrations needing correction due to a straighter path for light to travel. For whatever reason, third parties have more aggressively reverse engineered Canon’s proprietary mount and lens communication, resulting in adapters that not just include autofocus, electronic aperture control and image stabilization, but do it all far more reliably and accurately, with frequent updates to increase compatibility and improve performance. Purely speculating, I feel this may be a result of Canon’s democratizing nature compared to Nikon, with a larger market share resulting in greater sales volume and lens retail prices that tend to be lower than comparable glass from Nikon. Combining sales volume with a lower average retail price, the cost of used lenses is pushed even lower. This abundance of lower cost glass, and large fraction of camera owners, makes Canon a more appealing target for third parties to adopt and support.

So, I have my reasons, a specific brand and a lens mount… now for an adapter. I’ve chosen the TechArt Pro EF-GFX adapter. It supports EXIF, autofocus, image stabilization and electronic aperture control. My other options were the Fotodiox Fusion and Steelsring for “smart” AF adapters. The Fotodiox, while a bit cheaper, is just plain ugly. The Steelsring was just too expensive and I couldn’t find many firsthand reviews on its performance nor was I impressed by their rate of progress in firmware development. At $500, the TechArt adapter isn’t cheap but it looks discreet, firmware development is consistent due to backing from Mitakon, a brand that’s large and invested in the industry, and multiple firsthand reviews have rated it positively.

For the last “why,” why not the Fujifilm H-GF adapter? Little do people know, Fujifilm had a large hand in creating Hasselblad’s current H6D medium format systems camera. The progenitor of the series, the H1, was born from a partnership between Hasselblad and Fujifilm, and was the first medium format system camera from Hasselblad with autofocus. Because of that, Fujifilm was able to release their own version, the GX645AF, using the same HC lenses and H mount. Because of this, both Fujifilm and Hasselblad branded lenses work flawlessly when adapted to GFX and endows it with faster flash sync speeds far beyond the GFX’s 1/125s sync speed due to the lenses having built-in leaf shutters. When installed, the GFX gives users the option of using the leaf shutter or focal plane shutter as desired. Plus, these first generation HC lenses have since been superseded with HCD lenses on current H series Hasselblads and can be found relatively cheaply despite their rarity. So why didn’t I go this route? Because the leaf shutter limits maximum aperture size and the adapter alone is nearly $800. At that price, I could buy a brand new GF lens for the price of the adapter and a single HC lens.

And now for the details of this database. It will not be comprehensive either in the number of lenses tested or the performance metrics. I intend to keep it as simple as possible, like a virtual “go, no-go gauge.” Fortunately I have a few friends who shoot Canon, giving me access to more than a few lenses to test at no cost. As I get my hands on lenses, beginning with Sigma, I will list the specific lens, a single 35mm equivalent field of view (based on the 0.79x crop factor), and degree of electronic compatibility (AF capability, aperture control, EXIF data, stabilization, corrections). To allow you to judge for yourself, I will also include downsampled, full sensor images of a white background at the top and bottom of the focusing range, from stop to stop, at the largest and smallest apertures and at ƒ/8. Why ƒ/8? Because it tends to be the best balance between sharpness and a large depth of field for “full frame” lenses and is often the smallest aperture before diffraction sets in. Use of a sample at three different aperture settings will also show if any vignette at wide open changes as the aperture is stopped down. This should also address if “focus breathing” affects any vignetting. Most lenses exhibit focus breathing, a phenomenon where the field of view changes slightly during focusing; where you focus in a composition may introduce vignetting when dealing with image circles that cover the sensor only just.

In the case of any zoom lenses tested, I will only show image samples at the focal lengths printed on the zoom ring.

And that’s it. If you want more details than that, there are a number of resources already to be found, two of which are the GFX forum on Fred Miranda and Jim Kasson’s blog. The only problem is that neither are a comprehensive resource, with the former being especially difficult to sift through; between the petty, internet pissing contests and pedantic subjectivity masquerading as helpful, there is no order, standard or even consistent evidentiary samples. It’s rarely more helpful than being told, “visit your camera store.”

So, the database will be established in the next week, starting with the Sigma 50mm ƒ/1.4 DG HSM Art and possibly the 35mm ƒ/1.4 DG HSM Art and Canon 70-200mm ƒ/2.8L IS II USM.

To be clear, this is being done for my own benefit but I’m sharing my findings to help others. It’s not meant to be definitive or anything more than a simple “yes or no” answer to whether a lens is a good match for the GFX. I will not be taking requests of any sort, be it a specific lens, a specific metric, corner testing, MTR charts, provide original RAW files, etc. Any data I list beyond what’s outlined here is at my own discretion.

Just in case: Should this post, or others relating to it, be edited, know that this database is beginning in January 2020. Despite this, I hope what information I’m able to provide is useful to you but its use is your responsibility and to be used at your own peril. I will not be held responsible should you purchase a lens that doesn’t meet your performance standards.

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