Nikon’s 19mm, while a superb lens, is about the same price at a D850 body. As I said above, they allow you to reposition the plane of focus. Tilt/shift lenses do not give you more depth of field.
Just in passing, both Helicon Focus and Zerene Stacker, the two most popular focus stacking software programs, yield much better results that does Photoshop’s “auto-align, auto-blend” option. Focus stacking works best where there is a smooth transition of the subject you want sharp in the final composite image. The resulting stacked image often shows an obvious halo around that close object. Another problem happens when you have one frame with a close in-focus object positioned against a distant out-of-focus background, which has to stack with the reverse, the close object now out-of-focus but with an in-focus background. Software can fix some minor movement problems, but try photographing on a windy day and you’ll end up with a blurry stack. The first is subject movement from frame to frame. But, as always, there is a catch…or I should say, several catches. You’re basically getting a lot more depth of field, a lot more of the scene in focus, without resorting to small apertures and the resulting diffraction problems. These shots must then be combined using software (my choice is Helicon Focus as it has a RAW IN – DNG OUT mode). To do focus stacking you take several images with your camera mounted on a tripod, all at the exact same exposure, but at different focus distances into the frame.
Nikon, for example, offers 19mm, 24mm, 45mm, and 85mm tilt/shift lenses. On the other hand, a tilt/shift lens is a specialized fixed focal length lens that permits changing where the plane of focus is positioned. Focus stacking can be done using any lens. Focus stacking is a means of gaining sharp depth of focus (more near-to-far sharpness in the photo) while shooting at prime apertures. Here’s the short answer: these are two very distinct techniques. I’ve received several emails asking about the differences between focus stacking and shooting with a tilt/shift lens.