I remember trying your cup diffuser for a while, firing the flashes through a paper cup attached to the end of my MP-E. Tended to get in the way a bit at high mags when the insects nearly touch the end of the lens so I went back to my original flash head diffusion set-up. I've just noticed a lot of macros shot at higher ISO's and lower shutter speeds to get more background light in and just use the flash (if any) for a bit of fill. I still like the 1/250sec, F11, ISO100 camera settings with the full diffused flash. Sometimes the black backgrounds can make for a spectacular shot, like a lot of JohnK's earlier works.
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