Prior to this, I have been using my version of "cup diffuser" for the MPE65 1X-5X macro lens / MT24EX macro twin flash combo for a couple of months now and loving the light from it. More about the cheap yet great DIY Concave Diffuser here.
About a week ago, I tested out the "concave top diffusers". It looks like this:
the opening on the one on the right hand side goes onto the MT-24EX flash head. The one on the left is upside down for comparison
the same pair from a different angle
The opaque concave tops are from those toy capsules widely available from toy vending machines in most convenient stores/sundry shops in Malaysia.
how it looks like when fitted onto the MT-24EX and MP-E65
front view of the setup
The housing, as you can see, are from Justea packet drink (Tetra Pak drink packaging). It was actually quite a task to make the housing fit snugly onto the MT24EX flash heads. However, you can use this moldable plastic to make housings that fit nicely onto the flash heads.
Surprisingly, additional layer of diffusion from the concave top actually almost doesn't cause any loss of light as evident in the following quick tests:
without the concave top, i.e only with tent/cup diffuser. At 1:1, ISO100, F11, 1/200, i need 1/4th flash power to light the scene.
with the concave top and also the tent/cup diffuser i.e extra diffusion. At 1:1, ISO100, F11, 1/200, i need the same 1/4th flash power to light the scene.
Now the 100% crop images of the above:
without the concave top diffusers:
with the concave top diffusers. Noticeably nicer/less harsh specular highlight there.
However, even with the slightly better handling of highlight, my latest concave tops plus cup/tent diffuser still can't pass the ultimate test: the golden tortoise beetle! In fact, i failed miserably :D
blown highlight all over, even at -2 FEC (flash exposure compensation).
Maybe I need to look for some Vellum paper to replace the polyfoam sheet I'm using for the cup/tent? Still looking for a shop in town that sells it.
To be fair to the awesome tent/cup diffuser and concave tops, I need to point out that I had tried shooting a golden tortoise beetle with just natural light and still ended with blown highlight. But next time, I'll try to use a CPL.
Note: the concave top diffuser is the brainchild of SteB1 (Stephen). If you would like to read more about his excellent analysis of various diffusion methods, check out the following:
Some Ideas on Macro Flash Diffusion
Concave Flash Diffuser Test