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Fujifilm GFX Does not Always Focus at Full Aperture, Could it Be Compensation for Focus Shift?

See my Fujifilm GFX wish list and please bookmark my camera and computer wish lists for shopping at B&H and/or Amazon.com, so I get credit.

Regarding my post last year, Fujifilm GFX 50s Firmware Update Might Degrade Focusing by Stopping Down?.

Dmitri S writes:

After a lot of pondering I am beginning to build my own GFX50S-centric system; just purchased a barely used body. The plan is to use the GFX with adopted lenses, perhaps also with a CAMBO ACTUS MINI or a similar contraption I would build myself. That is why I was not planning to buy any native GF lenses, at least not in the beginning.

Now, I wanted to make sure the GFX 50S body I have purchased used is functioning as it should, with its native lenses. I went to my local photo retailer and spent some time there with the 110mm F2 mounted on my camera. Everything seemed to function well, except… this strange aperture behavior.

With camera in “A” and the aperture set to fully open (either with the aperture ring on the lens, or with the dial on the camera) I could hear and see (looking into the lens) the aperture blades contract and expand depending on where the camera was pointed. All the test shots show F2 as the recorded aperture setting. So - the exposures were taken at the F stop I selected, whereas in process of composing and focusing the camera was adjusting the aperture on its own. Very strange and bizarre.

This odd behavior was just like with my other mirrorless – the OLYMPUS OM-D E-M1 and legacy 4/3 (SLR) lenses. I have gone through two bodies before OLYMPUS admitted the faulty and wrong behavior and exchanged my camera for a refurb that finally (!) works as any normal camera should. It looked as though the early batches of that otherwise excellent little camera were faulty. Olympus indirectly admitted it, failed to fix my camera (at first under, later post-warranty) and had the camera exchanged. The saving grace was that I ended up with a working camera. And a lot of sour taste and second thoughts on ethics and corporate culture of Olympus.

ow back to FUJIFILM GFX50S – do you know of any cases or issues with “rattlesnaking” aperture in the native FUJI GF lenses, when the diaphragm blades live their own life out of your control? Is there a chance that my GFX50S body, just acquired used, (firmware 1.11) may be faulty? The FUJI tech support laid the blame on the lens, from my description of the experience. Is the GFX50S supposed to focus fully open or at the selected aperture setting? I know that different mirrorless camera lines exercise different schools of thought regarding how to acquire focus. Any insights or suggestions from your, albeit short, GFX50S user perspective?

DIGLLOYD: I have personally observed (with the new firmware, not sure about prior), that the Fujifilm GFX will *at times* focus at other than full aperture. At least with the GF 45mm f/2.8; see Fujifilm GFX Focus Shift Evaluation.

In general, in the field is that when the 45/2.8 is set to, say, f/8 or f/11, initiating autofocus sometimes *did not* fully open the aperture to focus, but appears to open it to about f/4.5. This is direct observation of viewing the lens diaphragm from in front of the lens to see its behavior as AF is initiated. Possibly Fujifilm might have (in firmware) an intentional workaround for focus shift behavior for point-and-shoot photographers shooting at f/4.5 and beyond.

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