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Reader Question: Adapting Medium Format Lenses to the Fujifilm GFX

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Jason W writes:

Have you attempted to adapt 3rd party medium format lenses yet to the GFX 50s? (i.e., Hasselblad and Mamiya).

I'm still a bit stymied how much of a failure adapting most 35mm lenses turned out to be.

DIGLLOYD: see my previous comments on the Hartblei 80mm f/2.8 SuperRotator for Nikon. Its optics are Zeiss medium format 6 X 6 in Nikon mount. It does not perform well on the Nikon D810 until stopped well down: its optics were designed for film and the light rays instead encounter a 2+mm thick chunk of glass in the way (sensor cover glass). It is degraded until at least f/8 on the D810 which is why I almost never shoot it, gorgeous though its rendering is. And it is even more degraded on the GFX.

Digital is not film; there is a chunk of glass with its own thickness and refraction characteristics sitting over the light sensing portion of the sensor (“sensor cover glass”). There are also aggressive micro lenses on the GFX sensor. See the excellent article over at LensRentals.com: The Glass in the Path: Sensor Stacks and Adapted Lenses.

The idea that medium format lenses are going to be better makes no sense in this context: if the lenses were not designed for the sensor cover glass, there are going to be problems. See the MTF chart for the Zeiss ZM 35mm f/1.4 Distagon on Sony mirrorless and its devastating loss of MTF—and there we are talking about one digital versus another (with cover glass of roughly 0.8mm for M vs 2.5mm for Sony for a difference of 1.7mm).

 
FotodioX Nikon F to Fujifilm G-Mount Lens Adapter

Lenses designed for film do not interact well with a 2mm or 2.5mm or 6mm (or whatever) glass plate in the optical path splaying light rays way off target. Thus it is unrealistic to expect anything but poor to mediocre results until f/11 or so.

As far as I know, it is not even possible to optimize a high performance lens for both Canon and Nikon digital SLRs without making specific tweaks for small differences in sensor cover glass. I am pretty sure that Zeiss does this for Otus lenses, but I wonder if Sigma slightly adjusts element spacing for each optic in the Art lenses, and for which system the design is natively superior—I’m guessing for Canon bases on my disappointing results with the Sigma 85mm f/1.4 DG HSM Art.

That a lens is designed for 35mm or medium format or large format is not the issue since that’s an issue of image circle size. It is the sensor cover glass that is of concern. On the GFX all of the 35mm format lenses I tested were severely degraded even on the central 36 X 24mm area of the sensor.

So while there may be a few lenses that perform well*, there are likely to be very few and these are almost all likely to be those that are long focal lengths—135mm on up. With these lenses even with a 1/3 plate displacement of focus, it won’t matter too much because the ray angle is favorable, so that a few stops down things might look quite good, e.g. the Zeiss 135mm f/2 APO-Sonnar performance at f/4.

Bottom line: stick with native lenses for best results.

* It can also be that a few lenses actually improve in localized areas of the frame due to the sensor cover glass in effect correcting astigmatism. Yet in other areas astigmatism can become much worse, ditto for chromatic errors. But on the whole, there will be a large quality loss.

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