I recently got back from a trip to Kaua'i. I had a bunch of new (well, used but new to me) gear including a Sea & Sea YS-D1 strobe. Unfortunately, my plans for a closer, less exotic trip to practice with the new equipment got scrapped so I had to practice while in Kaua'i. In short, in many of my shots the strobe coverage was cut off for 1/4 to 1/2 of the exposure. It's a very artificial cutoff - I'm sure my strobe positioning was not good for all shots, but this seems like something different. The problem did not happen with all shots, only some. I couldn't identify what conditions were causing it for some shots and not others. Distance to subject and relative strobe position seemed to have some influence but I couldn't pin it down. I saw it in portrait and landscape shots. I usually shoot macro with the strobe above the housing, but I also saw it with the strobe moved to the left of the housing.
Equipment used during issue:
Canon 550d, Canon 60mm Macro Lens, Sea & Sea RDX-550d Housing, Sea & Sea RDX Standard Port, Sea & Sea YS-D1 strobe (1)
I have previously shot with a single YS-110a strobe and did not have this issue. When I shot with the YS-110a, I always used the diffuser. I also used the Diffuser 100 with the YS-D1 and I'm wondering if this is the issue. Unfortunately, I didn't come up with this theory until the very last 15 minutes of my last dive, so I didn't have time to really verify if removing the diffuser made the issue go away.
d1issue1 - more than half cutoff
d1issue2 - portrait example
d1issue3 - 10% cutoff, but still present