In an interview done with a Fujifilm senior product planner, it was said that XF-mount lenses are incompatible with IBIS, and that Fujifilm does not want to sacrifice image quality. But in the recent launch of the Fujifilm X-H1, IBIS was introduced. I'm not sure whether the image quality is compromised with the IBIS, or has Fuji finally found a solution that can do this without any degradation of IQ?
In the interview, Takashi Ueno of Fujifilm explains why he thinks the XF lens mount is inadequate for in-body IS - shifting the sensor means some parts of the sensor will be shaded by the mount. In other words, the ideal lens mount should be larger diameter.
Now, is the image quality compromised in the recent Fuji X-H1, featuring IBIS? According to the above statement - yes, it is compromised. But I doubt the difference is easily noticeable. It is just a little bit more vignetting. After all, and we get some vignetting all the time, regardless of the image stabilization. Fujifilm's small APS-C sensor enjoys plenty of space behind their XF mount, compared to the Sony full frame cameras using only 2 mm wider Sony E-mount.
Alternatively, we can guess that the Fuji guy simply wanted to turn the camera's deficiency into merit. Look, our competitors offer IS, but we don't and this is good, because it means better quality. Now, 2 years later, let's forget about it, IS is now good because we have it as well.
- We consider a lens with unwanted tilt or shift to be less than ideal because either affect image quality in one way or another.
- We also consider motion blur caused by camera movement to be less than ideal.
In the case of image stabilization, whether based in the camera or in the lens, we accept a very slight amount of misalignment of the lens/sensor system in exchange for reduced blur due to camera movement. This is true of all image stabilization systems, either lens based or camera body based.
- Lens based systems use tilt movements.
When the lens' IS element is tilted in any way away from exactly perpendicular to the center of the lens' optical axis there will be a slight reduction in image quality in terms of overall sharpness. The slight tilt induced by lens based IS will also affect things such as astigmatism and other aberrations as well.
- IBIS (In-Body Image Stabilization) systems use shift movements.
Movements that keep the imaging sensor perpendicular to the lens' optical axis would, in theory, not affect image quality in the same way that tilt movements do. But shift movements introduce issues of their own. By moving the center of the imaging sensor away from the center of the lens' optical axis one side of the frame will be moved into the edges of the image circle that would otherwise not be used. For most lenses, image quality is greatest at the center of the image circle and poorest at the edges. There are exceptions with regard to some aberrations for some lenses, but for the most part this is generally true. Vignetting, for instance, would be affected by shift movements. The direction towards which the sensor moves would become darker on that edge. The opposite edge that the sensor moves away from would be brighter.
From the promotional materials linked in the question, we are told the IBIS system will only be active when used with Fuji lenses that do not have in-lens stabilization.
The correction is based on five axes (up and down / right and left pitch, yaw angle and optical axis rotation) to achieve more than five-stop (up to the equivalent of 5.5 stops* ) image stabilization when the camera is fitted with any FUJINON lens that does not feature the optical image stabilization functionality.
So it appears that either the XF lenses with stabilization will not be compatible with the new IBIS system or, at the very least, Fuji has decided to disable IBIS when lens-based IS is available. One would assume that this is because Fuji considers the lens based IS to be better than their IBIS in some way.
This is an indication that either:
- The lens based IS without IBIS is more effective than IBIS without lens based IS. At least for these lenses.
- The reduction in image quality due to tilt of lens-based IS is less significant than the reduction in image quality due to the shift of the new Fuji IBIS.
- There is a fundamental way in which the lens based IS systems in Fuji's XF-mount lenses with IS are implemented that makes them incompatible with the new Fuji IBIS system introduced with the Fuji XH-1
In either case, now that Fuji has introduced a camera with IBIS, they are backstepping a bit away from their earlier statement that the XF-mount can not accommodate IBIS without some loss in image quality.
It seems to mostly be marketing doublespeak.
When Fuji didn't offer a camera with IBIS (In-Body Image Stabilization), the negative effect on image quality, however minute it might be, was emphasized as being significant enough to affect the user experience.
Now that Fuji offers a model with IBIS, the same effect on IQ is, according to Fuji, no longer significant.
The interview was from sales&marketing, engineers may well of been slapping their foreheads and groaning.
My guess is that given a potentially perfect image, if IBIS is switched on then it will be degraded, but given a shaking camera and so potentially imperfect image, introducing IBIS will make it less bad.
So the sales guy was kind of right with his facts, he just came to the wrong conclusion. It must be difficult when everything you say is recorded and played back when you contradict yourself. So they managed to do a thing they said they could not do, to me that is a good thing.