SLC-1L-04: A Hack for Manual Flash at Sunset



Manual flash is great for its consistency and repeatability throughout a shoot. But working in a fluctuating ambient environment, such as against a fast-waning sunset, can get hairy.

So here's a neat little trick to easily control the exposure level of both your subject and background in a fluid environment without your eye ever leaving the viewfinder.


Some Things to Remember

First, some basics. When shooting against a sunset, our ambient exposure will be set to record the sunset. This will leave our subject in silhouette. And that gives us a black canvas upon which to add our artificial light.

Let's say, for example, that our sunset exposure is 1/60th at f/5.6 at ISO 400. To light our subject, we'd simply place our flash at the desired location, then dial up (or down) the power level to light the subject to f/5.6.

No matter how we recompose as we shoot, the distance between our off-camera flash and subject are not changing. So the flash exposure will remain constant. Which, of course, is what makes this a better approach than TTL lighting, which can vary wildly when you recompose—especially against a darkish sky.

Now remember, the sunset exposure is going to be steadily decreasing—especially in the waning dusk. The quality of the light gets better even as the quantity goes to hell in a handbasket. You're dropping your shutter speed to keep up, and hanging on as long as you can.

When the shutter speed gets too low, you can always take a couple stops of power out of your flash, open up your aperture to compensate, then get back a faster shutter speed to compensate for the wider aperture. Rinse and repeat as needed, or until you run out of aperture.

But re-metering the sunset and constantly opening up the shutter to compensate can a pain. So first step, let's leave the flash on manual, and get the camera off manual.


Lock the Aperture, Float the Shutter



Yep, we're switching to aperture priority. Think for a second about what that "A" mode gives you. You lock in the aperture (which is what the flash cares about) and the shutter speed floats. Meaning, the shutter speed will keep up with your waning sunset automatically.

This is pretty much exactly what we want, right? We have removed the task of metering and adjusting our shutter for the sunset. So now we can concentrate on our subject.

But wait, it gets better.



The exposure compensation dial, seen above, will alter the exposure relationship between the aperture and our automatically adjusted shutter speed, allowing you to over- or under-expose the frame without changing the aperture.

Which, if using manual flash, is exactly what we want.

This means that the exposure compensation button becomes a dial to vary the amount of drama in my sky. For instance, here is is, set at +-0:



That's what the camera thinks the sky should look like. But as far as drama, it's pretty meh. For the record, my aperture is set to f/6.4 here. But the camera really doesn't care. It's just gonna let the shutter speed ride to get a "normal" exposure for teh ambient. Which in this case means the sky overwhelming the frame.

Now, if I were to set my exposure compensation to -1, just by rocking the dial with my right thumb, the camera will now underexpose the sky by one stop. But Aiden stays where he is:



Which is exactly what I did above. And I just got my dramatic sky back, and it'll stay at that minus one stop ratio as the ambient light changes.

Let's rack it down even further. What the heck, let's go -2.3 stops:



Now we got drama out the wazoo. So, even in a changing environment, I can instantly and easily move my sky anywhere I want it to be, tonally speaking. Better, the shutter float in aperture priority will keep it there. And since the aperture and the flash remain constant, Aiden's exposure will remain consistent.

Remember, when using flash you are still subject to your camera's maximum sync speed on the shutter setting, even if you are in "A" mode. So don't break that speed limit.


Easy and Fluid

It's hard to overstate just how quick, easy and intuitive this technique is during a shoot. But here's a good way to show you.

In the three photos above, note the jet trail in the sky just to the right of Aiden's glove. Because of the position of the jet, you can see just how quickly these photos were taken.

And honestly, I was not even trying to be fast. I was just shooting. I saw the jet trail thing after the fact. (And with the exception of the top photo, these are all straight out of camera for illustrative purposes.)

But wait, it gets better.


Tweaking the Subject Exposure



Let's go back our exposure compensation setting of minus one stop. I like the sky right about here. And remember, my aperture is set to f/6.4. And Aiden looks pretty good here. But what if, hypothetically speaking, I wanted to change the exposure on him?

You see where this is going, right? Flash distance and power remaining constant, our aperture ring now controls Aiden's exposure.

Let's overstate it for effect. Normally, I'd be looking at 1/3-stop adjustments. But let's rack our aperture down to, say, f/10:



With flash power and distance remaining constant, down goes Aiden. But since we are in "A" mode, the shutter speed automatically adjusts to compensate. Result: our sky has not moved.

Now let's open up our aperture setting. Like, a lot. Say, f/4.5:



Now we have Aiden back—and then some. This is overdone for effect. But you get the idea. Aiden is now 2 1/3 stops brighter, but the sky has not moved.

And again, note the jet trail positions. This is all quick, and effortless. It really doesn't even require conscious thought once you get used to it.


Controlling the Whole Environment

So your right thumb (via the exposure compensation) controls the sky. And your left thumb and forefinger (via the aperture ring) control the subject. And you stay behind the camera during the fast-moving light of post-sunset. Pretty cool, huh, considering you are lighting in a fluid ambient environment, with manual flash.

Next time, another tip to make your sunset flash photos look even better.


FROM: Strobist Lighting Cookbook, One Light


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