I bought a set of 40mm extension rails for the Fuji GX680.
Gave them a test today with a roll of Kodak Portra and some veg from the kitchen!
I have also got a set of 80mm extension rails coming soon, along with a set of extended bellows.
The standard bellows on the Fuji are virtually at full stretch with the 40mm rails, thus, the extra length version is definitely required for macro work. How much macro photography I end up doing with this set up remains to be seen of course.
Reciprocity compensation has to be factored when using bellows on any camera for macro/ close up work. Thankfully, it’s relatively easy to work out and I have to allow approximately one stop over to get proper exposure.
If you use bellows with no reciprocal compensation, you’re very likely to end up with underexposed photos.
A small explanation below along with a few photos.