The other day I picked up a copy of Zack Arias’ OneLight Workshop DVD at the advice of a friend. A few glasses of scotch and some time later, I ended up sending these thoughts to that same friend:
Dude, I am at the 15:25 mark of DVD 1 from the OneLight workshop. I must say that this guy is not doing a convincing job of articulating how a camera and flash works.
At 4:57, he drilled into us that “shutter speed controls ambient exposure” about 13 times in 60 seconds. This is a reckless oversimplification [as we'll see in a moment] but goddamn it sounds like the gospel the way Zack preaches it. Like Moses himself stumbled upon this bit of wisdom scrawled on a stone tablet and had simply forgotten to mention it when he came off the mountain.
Now, almost 11 minutes later, he says, “Let’s say we’re getting f/5.6 at full power, but we want to control a bright ambient light source, so we need to be at a target aperture of f/16.”
Wait … wha? *blink* I thought shutter speed controlled ambient exposure … ? Moses himself was supposed to say as much but forgot to, right?. Why am I thinking about the aperture now?
In a fit of sobriety the next day, I ended up watching the rest, and concluded that I am glad I did. Zack is a skilled photographer and executes his craft with a great deal of proficiency. No doubt about that.
But back to the email. The part that got under my skin was that the statement about shutter speed controlling ambient exposure is accurate but incomplete. This would have been fine with 95% of viewers, except that just a few moments later, Zack goes off on a tangential (unimportant?) explanation of the power of speedlights vs. monolights, and an exception to his shutter speed commandment is at the heart of the entire segment. The complete commandment should read something like this:
Shutter speed controls ambient exposure except when your maximum flash sync speed would be exceeded.
For those of you that “get” this already, you can probably skip the rest of the post. But if you saw this DVD and were at all confused by that segment and/or you don’t buy the proposed amendment to the shutter speed commandment above, here’s a quick example. Let me run out onto my front stoop with a camera real quick …. be right back …
1/250th sec @ f/5.6
OK, so I have made some photographs of my front door to illustrate. This first image was made at f/5.6 with a shutter speed of 1/250th of a second. It looks OK at first glance, but the trim on the left is blown out and the door itself is a tad bright compared to reality. So, if I were to put a subject in front of this door and make a photograph using a flash, I’d want to darken things a bit … but uh-oh: I am already at my maximum flash sync speed of 1/250th a second. My only option to control ambient exposure at this point is to stop down the aperture.
1/250th sec @ f/8
This image was made with the same shutter speed (do I have an option?) but stopped down to f/8. This would be a more accurate rendition of the door and I could control my flash exposure on a subject in front of it using the output controls on the flash itself. (If I had it right in the first image, I’d need to provide one more stop of light to keep my exposure constant.) But what if I wanted an even darker background?
1/250th sec @ f/11
Voila. I’d could go to f/11 and increase the light from the flash by another stop. (This is where Zack starts talking about how a typical speedlight runs out of power compared to a monolight …)
So, given that you can’t exceed the maximum flash sync shutter speed while trying to control ambient exposure using a flash, your only option is to stop down the aperture. And this is why Zack and Moses’ “shutter speed controls ambient exposure” commandment needs the amendment.
Shutter speed controls ambient exposure except when your maximum flash sync speed would be exceeded.
