Overexposure problem using TTL (Olympus E-M1)

On my first dive trip with the Olympus E-M1 and the Nauticam housing, I had a problem using TTL. I think it showed up the most with medium distances using the 60mm macro lens. I was using two YS-01 strobes.

I have some examples of the problem. All of these are shot with the mode dial on manual. The metering was center-weighted. Here’s a pair of flamingo tongues that were overexposed when shot at 1/320^th and f6.3:

My reaction was to drastically change the f stop, so the next shot was OK 1/320^th at f 14.0:

Same dive, here’s a toadfish overexposed when shot at 1/320^th and f 8.0:

Again, I stopped the camera down, and the next shot was OK at 1/320^th and f 14.0:

Here’s a shot that had OK exposure at 1/160^th at f 6.3:

But then the very next shot (different subject), is way over-exposed when also shot at 1/160^th at f 6.3:

The same scene is better exposed after drastic changes to the shutter speed and aperture, this time 1/320^th at f13.0:

Any ideas what I was doing wrong? Could I have had the flash setting on “full” rather than “fill”? Would that explain this?

I can't see any photos here but from the text descriptions it sounds like your strobes were set incorrectly. If the strobes are set to TTL and the camera flash setting on fill, you should get the same foreground exposure with large or small apertures, with the larger apertures giving you more ambient light in and smaller apertures giving a darker background. You might try all the combinations at home to see how they work with your setup.

thanks for the reply. I'll have to figure out why the photos didn't post. I haven't done this before.