Out of the box the F6 is set to display possible shutter speeds from 1/8,000 of a second to 30 seconds. After 30 seconds the camera has the customary “bulb” setting, allowing you to trip the shutter manually (with something like the MC-30 cable release) for as long an exposure as you can hold the shutter release down for.
Custom setting B5 in the CSM provides the capability to extend shutter speeds beyond the default 30 seconds, unlocking extended shutter speeds before reaching the Bulb setting. When this option is enabled, after 30 seconds, you’ll see 40 seconds, then 50 seconds, etc. all the way up to 30 minutes before you reach “bulb.”
For some photographers this is an advantage if you do a lot of night shooting, for example, and exposures typically run between 30 seconds and 30 minutes. For others that use the bulb setting frequently, it’s a disadvantage because you have a lot more spinning of the main command dial to do until you get to bulb. But at that point you’re not relying on the camera’s recommended exposure and instead, winging it.
I see it as an advantage because the meter on the camera is capable of resolving exposure well beyond 30 seconds. For the above exposures the longer times weren’t necessary for the final shot because between f8 and f11 the correct exposure came in between 10 and 20 seconds. But- having the ability to dial down the aperture and lengthen the shutter speed and get an accurate meter reading was helpful determining the final exposure.
Film: Ilford HP5+, developed in Ilford DDX.