Safari Mk1 has quite a long flash duration so works well with tail-hypersync - longer duration reduces the fall-off in brightness that inevitably occurs from bottom to top of the image as the flash pulse fades, usually around a couple of stops - sometimes a bit less, sometimes quite a lot more. It varies according to flash unit, power setting, camera model and shutter speed. Some triggers allow you to adjust the timing off-set to optimise settings.
Ways to reduce fall-off:
- Shoot in daylight, so the ambient light masks the flash fall-off. By the same token, avoid plain backgrounds with low ambient light, eg studio!
- Keep the main subject away from the top and bottom of the frame so avoiding the extremes of fall-off.
- Just doing these two things is often all you need.
- Use the inverse square law by positioning the light close to the subject on the pentaprism side of the camera, ie from above, or turn the camera vertical if the flash is left/right. With the light close, there will be a natural ISL fading in brightness that - if you're lucky/cunning - will neatly counter-balance the tail-hypersync fall-off.
- Sort it out in post processing, with graduated filter and local adjustment tools.
The ND filter method avoids all these issues, providing you don't need a fast shutter speed to freeze movement. The filter just darkens the whole image, so you can stay under the x-sync limit and maximise flash brightness, with no side-effects. Two or three stops ND is about the limit, before the camera's viewfinder gets too dark for easy working.