The F280 can be used in two modes. In the normal mode, it works like any normal flash in TTL auto mode. That means the camera, in autoexposure mode, automatically sets the shutter at the X-Sync speed, which is 1/60 with the OM-4T, and it cuts off the flash when the sensor in the camera sees that the subject has been properly exposed. The F280 works fine in this mode, but has the serious disadvantage of not offering bounce capability. I solved that by using a stroboframe bracket and Olympus's TTL Auto cord.
The other F280 mode is the FP Sync mode, which is designed for use at shutter speeds of 1/60 and above, all the way to 1/2000. This is mainly used for fill flash, but the metering is not nearly as sophisticated as the auto-fill flash modes used on more modern 35mm SLRs like the Canon EOS-1 and Nikon N90. One problem is that in FP mode, the flash just isn't very powerful. I don't have the chart in front of me, but I think that shooting at 1/1000 of a second, you have to be like 3 feet away from your subject for correct exposure!
Because of the primitivity of the FP mode and its low power, I always use my F280 in normal TTL auto mode. Olympus made another flash, the T32, that offers bounce and is, if I remember right, a bit more powerful than the F280 (but without offering the FP mode). For normal flash photography, the T32 is probably the best choice.