Let’s be clear about three things:
1. Joe McNally is one of my favorite photographers and I learn something new every time I look at his blog.
2. Joe’s work for National Geographic and a bazillion other publications is great not only because of excellent execution, but also because of the quality of Joe’s ideas.
3. Joe’s images speak for themselves, and I’ve never produced a single frame as good as his worst published work.
Okay, now I’ve got my asbestos underwear and diamond-shell kevlar helmet on, so here goes: I don’t think Joe understands how Nikon’s Through-The-Lens (TTL) Flash Metering works.
At today’s FlashBus event in Los Angeles, Joe walked us through a variety of lighting set-ups using the TTL system. These were all studio-type shots, and I didn’t see any advantage to his use of TTL metering. In fact, I thought it overcomplicated everything, requiring that Joe independently adjust exposure compensation for the camera and flash units. His whole approach to TTL seemed like a giant, continuous workaround. In a fast-changing environment, TTL is a life-saver, but I wanted to understand why Joe uses it in carefully constructed shots.
During the Q and A, I asked what advantage he got from TTL in these cases. He answered that he liked to control the flashes from the camera. So do I, but that’s a feature of Nikon’s Creative Lighting System (CLS), and works whether we use manual, TTL, or other exposure settings. TTL is a metering option that automatically sets the flash power based on light reflected by the subject, presuming the subject is in the center of the frame. And that’s what either Joe or I do not understand: My interpretation of the manuals is that the flash metering and camera metering systems work together, but they are separate systems. And the flash system ALWAYS METERS FROM THE CENTER OF THE FRAME.
That’s why Nikon cameras feature a Flash-Value Lock (FV) button, and that’s why Joe’s off-center subjects started out overexposed against dark backgrounds and underexposed against light backgrounds. He adjusted for this and produced better images on the fly than I could do with a full day in the studio, but that’s not the point.
While Joe and David Hobby (another hero!) assured me that both methods were viable – and missed my question, I thought of one reason Joe might like using TTL. During the shoots, he sometimes changed light modifiers, e.g. stacking one diffuser over another. In those cases, TTL would compensate for the new layers. Joe could change the quality of the light while maintaining the quantity of light. That sounds useful to me.
I use TTL quite often, and I use the FV button for off-center subjects, as instructed by Nikon. It works great. I am more inclined to use manual settings with multiple, off-camera flashes. I was hoping to learn why Joe uses TTL in his multi-multi-multi-flash extravaganzas, and what advantages it might offer. I repeat: the quality of Joe’s work illustrates how unimportant these technical matters can be, but novices in the audience deserve a clearer explanation.
I wish I had more than 14 readers, because I know someone out there has the answer. Paging Mike Kichaven?
Oh, and I should point out that today was still the single greatest day of photographic education I’ve ever gotten – I can’t wait to photograph Antigone rehearsals this weekend!
EDIT 03/19/11: Just thought of another advantage to shooting remotes in TTL. CLS commander units can adjust TTL in 1/3 stop increments, whereas manual adjustments can only be made in full stops.