Long version: The Fujinon GX system is a robust professional 6x8 medium format camera that provides movements on a full range of lenses, from 50mm through 500mm. People still use this system as intended, but judging by the sale price of the equipment, it’s not popular.
Wikipedia has a good article that provides pictures and information about the lens lineup. https://en.wikipedia.org/wiki/Fuji_GX680
Some lenses from medium format film cameras are in heavy use on digital medium format cameras today because they’re easy to adapt. Pentax 645, Mamiya 645 and Hasselblad V are examples. Fujinon GX lenses are not readily adaptable; I have yet to encounter someone who uses them on a digital camera that isn’t the GX680 with a medium format back. The lenses are large, boxy, and just about impossible to attach to anything other than a Fuji GX680 camera body. As a result, they sell for very little money.
For most people looking to adapt lenses on digital medium format cameras, there are easier choices. I use many lenses that are smaller, lighter and don’t require rebuilding the lens. However, I was intrigued by the Fujinon GX line because it has a massive image circle (120mm for all but the 50mm f/5.6) and the lenses have register distances that work well with my setup and allow for huge movements.
I first looked at the GX line because I wanted a 250mm lens for my Toyo VX23D and Fuji GFX 50R outfit. Large format 250mm lenses don’t work because the register distance is too long for the VX23D body (unless custom long bellows and rails are used). Good medium format SLR lenses in the 250mm to 300mm exist, but they’re too long and heavy for my setup. For example, I’ve heard good things about the SMC Pentax-A 645 300/4, but that lens weighs 1,360 grams and is not usable on my VX23D.
I nearly passed over the GX line because of the awkward lens housings, but then I stumbled across a picture by a person on Flickr (Nokton48) who removed the lens cells from the Fuji housings and remounted them in various scavenged shutters for use on his Plaubel Makiflex. Ah ha!
I started with the 250mm f/5.6, and now also have the 210mm f/5.6, and the 65mm f/5.6 – all rehoused and remounted for use on my Toyo VX23D plus Fuji GFX 50R outfit. I have excellent lenses in the 65mm range already, but I bought the GX 65/5.6 because I’m exploring tall vertical stitched panoramas that begin with the centre of the image circle and go up; I needed a large image circle for what I have in mind, and the GX 65/5.6 is the only lens I’ve found that has the image circle and works on my camera; large format lenses like the Fujinon SW 65mm f/5.6 do not work because their register distance does not allow the needed shift of 30mm or more on my setup.
A "proof of concept" test image. Inspired by Lois Conner's 7x17 banquet camera vertical compositions, I'm exploring tall images that start at a normal viewing perspective. This requires a very large image circle to allow 30mm of rise from zero.