Most large format lenses are mounted in shutters, as focal plane shutters for large format are extremely rare. Barrel lenses don’t have them, and are generally used with very slow film and historical plate processes, where the shutter time is long enough that you can just remove the lens cap to make your exposure. What happens when you want to use a barrel lens with modern, faster film?
Enter the Jim Galli shutter, which is a free DIY arrangement:
Drum roll please. The world has been waiting for me to invent this.
Having just purchased a few old LF lenses without shutters, I actually have been waiting for him to invent this. Check it out at APUG.