Digital TTL that really works

During our last Digital Master class in Key Largo, Basim Nasr showed up with a brand new Seacam housing for a Canon 1DMKIII and a pair of Seacam Seaflash 250 strobes. I was very eager to see how his strobes performed on the exposure slate test, whereby we have a set distance and shutter speed, with the only variables being strobe light output and aperture. If TTL works, then the light on the exposure slate should be the same. As an aside, I have rarely seen a digtial TTL test that truly worked underwater. This one did.

Look at F-5.6. It is a little overexposed because there is too much ambient light on the scene. And, F-22 is a little too dark because there is not enough power in the strobe heads to light the scene at such a small aperture. But, within the range, F-8, F-11, and F-16, the exposures are very excellent and the histograms perfect. The backgrounds are different, but that's what you would expect from the varying aperture/shutter speed combination. The critical variable, the amount of strobe light striking the exposure slate, is impressively constant.

Thanks to Basim for sharing this data with us.