>TTl-BL was straightforward to configure, and worked great. >They do say, however, that it isn't ideal for repeatability. >Any slight shift in surface texture or angle of backlighting >can shift the results. > >The road got rocky for me in trying to use the flash as the >primary light. To eliminate ambient entirely and get accurate >exposure of about 60 paintings with subtle coloration and low >key saturation.
TTL-BL was not designed for the flash to be primary light. It was designed to add the flash to the ambient. When you want the flash to be primary you should use regular TTL with the shutter set high enough to eliminate the ambient.