1° Problem: Hotspot
There are two possible solutions, the focus light or the strobe itself
The white hotspot is most likely the light from your Nano LED focus light, even if this focus light should switch off when you take the picture but
something probably don't work well.
If the same issue occurs when you don't use the focus light it is the position of your strobe and only the lower intensity border of the strobe beam hit the coral
while the center of the strobe beam hit above and lead to the overexposed area.
2° Problem: Strobe positioning
very near macro with a external strobe (if not a ring strobe) is difficoult using 1 strobe only as he has to be positioned very near the port.
Using only 1 strobe in a 45° angle mostly lead to ugly shadows of the opposite side of the motive, positioning it above may work better.
3° Problem: Backscatter
To reduce backscatter you need to position the strobe(s) at a 45° angle regarding the lens and as far out as possible so
that the motive is hit only by the borders of the strobe beam
\ o /
o=Lens \ + / = strobe(s)
- why don't you use sTTL? The S120 and the S2000 should work perfectly together using Tv or Av, Av to control depth of field, Tv to control dark backgrounds
- play with the exposure control settings: matrix, center weighted or spot to see what gives you the best results
- backscatter and macro is difficult to control, photoshop is your friend ...
- If viz is good, the mix of the internal strobe and a external strobe can lead to very nice pictures