Shutter type has absolutely nothing to do with manual or automatic aperture control. Shutter type has absolutely nothing to do with transfer of lens metadata.
Agreed; Phase could have just as easily put their FPS inside the XT and developed an “X-aperture” for the lens that does everything the x-shutter does, minus the shutter part. Heck, they could have put an FPS inside the XT AND released the x-shutter as is and give the user the choice between leaf, FPS, and electronic shutter.
Obviously these options could result in higher R&D costs and/or costs to the end user and are not “just as easy”, however all could have been possible should they have been Phase’s design goal.
You are, of course, both right on the technical merits. However, from a practical perspective the two are very closely linked as far as product design / product management goes.
The core of the XT lens lineup is the Rodenstock HR series. Other lenses are possible today (Schenider digitar, Canon, Hassy 500) and others (Schneider LS BR? Hassy? Contax?) can be added to the roadmap based on
user feedback. But I expect the Rodenstock HR series will forever remain the core lenses used by most XT users. They are incredibly sharp, and they have image circles designed for 645 sensors + movement.
These lenses do not otherwise have electronic control. Since simplifying the tech camera workflow is a core design goal of the XT it's important to have electronic control and integration into the system; for example the ability for the back to control the aperture for live view, capture, and bracketing purposes, and for there to be metadata for the lens model and capture aperture for automatic lens corrections.
So the XT definitely needed something to provide electronic control of a Rodenstock HR lens. It ALSO needed some sort of shutter (as sensor-based ES is very useful in many situations, but is limited in terms of moving subjects and flash sync speed).
So how can we solve these two needs: Electronic Lens Control Need and Shutter Need?
One way to solve the Electronic Lens Control Need, the way that Phase One chose, is to put an electronic shutter+aperture unit in the lens (the X-Shutter) and design the body to pass the electronic connections of the lens to the back. This also solves the Shutter Need. Two birds with one stone.
If Phase One chose to pursue a Focal Plane Shutter (FPS) in the body this would have addressed the Shutter Need but, in and of itself, would not have done anything about the Electronic Lens Control Need. As you correctly point out the two are "unrelated" in an engineering sense so adding the FPS has no effect on the Electronic Lens Control Need. So if adding an FPS would mean you'd need a separate solution for the Electronic Lens Control need.
Now, as Matted points out, Phase One could have
absolutely done both: a Focal Plane Shutter (FPS) in the XT body and an "X-Aperture" for each lens. However, the result would be a "worst of both" situation in many ways:
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The limited durability of an FPS. Maybe not a deal breaker for many users, especially shooting landscape. But it is, none the less, a clear advantage for an X-Shutter that it is expected (and tested) to last a million captures.
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The increased vibration of an FPS. Maybe not a deal breaker for many users since it only affects certain combinations of shutter speeds, lens length, and tripod/head combos.
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The decreased design flexibility imposed by the mandatory space taken up by the shutter. I can't say more about this since some of the ideas that might take up this space are not public.
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The decreased battery life due to the higher power required to run an FPS vs LS. Carrying an extra battery or two on a longer shoot/trip, of course, is not a big deal, but the XT is built as a Field Camera explicitly with travel-friendly form factor as a high priority, so it runs against its goals.
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The lower flash sync speed of a FPS vs the 1/1000th of the X-Shutter. Of zero importance if you don't use flash. Of varying importance those who use flash depending on when/how they use flash. For some: quite important.
In addition I don't expect an X-Aperture would be necessarily less expensive. An X-Aperture would still require mounting/calibration, an aperture, new housing, and new electronics. Moreover, much of the X-Shutter (including the firmware, software, and mechanical design and testing) comes from developments done in the Phase One Industrial/Aerial division, so didn't carry the full development cost of a new product. An X-Aperture would certainly share some of that, but anytime you make significant changes to a product there is considerable overhead of branching development into a new product (new firmware, new testing, new housings etc). So you likely wouldn't get any cost savings per lens. Notably, by adding the FPS you would get the 1/4000th max mechanical shutter speed which would be useful for fast moving subjects (the sensor-based ES of the IQ4 can do 1/4000th but will exhibit rolling shutter effect on fast moving subjects) and that could be of value to some shooters. You would also gain faster flash sync speed (1/125s instead of 0.3s) for 3rd party lenses that don't have a shutter, though I expect most XT users will be using lenses that do have shutters (e.g. XT lenses, LS BR lenses, Cambo lens panels with copal shutters).
Matted also suggests the possibility they could have done both: an X-Shutter in every lens and an FPS shutter in the XT body. The tinkerer inside of me actually likes this idea quite a bit. But the XT is clearly and unapologetically targeting weight, size, and simplicity as its highest priorities other than image quality. For this to really hit home I think you need to pick one up and use it. We have an article where we compare its weight and size to other cameras and it's pretty surprising.
https://phaseonext.com/the-xt-is-smaller-and-lighter-than-you-think/. Having both shutters I think would clearly play against that goal and would make the system even more expensive. But I do like the idea from a "have it all" perspective!
In conclusion, there would absolutely be a few advantages to adding an FPS, but the disadvantages play against the core goals of the XT. How those balance for any given user is of course going to depend on their needs/wants/priorities. If the benefits of a Focal Plane Shutter are very important to the work you do then the XT is clearly not a good solution for you! That's okay! There are lots of good solutions out there that differently prioritize different pros and cons. From the clients I work and the conversations I've had in the last few days, I'd say the vast majority will not miss a FPS and will enjoy the benefits of the X-Shutter, but "vast majority" is not everyone!
