When in Auto mode, the ZOOM function on your Speedlite was intended to make flash photography simple for people who don’t know what they are doing. When paired with a compatible lens, your Speedlite will reposition the flashtube so that the its angle of coverage is matched to what the lens sees. The range, on a full-sensor camera is 24mm to 105mm. Then, if you pull out the flip-down Wide-Angle Diffusion Panel on a 580EX/EXII, the angle of coverage expands to 14mm (with a 3-stop loss of light, see the end for details).

The idea is that if you are shooting a 50mm lens, then there is no point in lighting the area covered by a 28mm lens. For on-the-fly photojournalism, Auto Zoom is a good feature—even if you know what you are doing. From my perspective as a creative Speedliter, the ZOOM button is a built-in modifier that I can use to change the look of the flash to fit to my vision.

Brightness Concentrates

The effect of the Speedlite zooming to a longer focal length, it is it concentrates the light. So, at the center of the frame, the Speedlite is brighter when zoomed to 105mm that it is when zoomed out to 24mm. You can see this effect in the frames below. They are all shot with the Speedlite’s power in Manual at 1/1.

As you can see, the is a distinct difference in the light on Tony’s face between the top frame (zoom = 24mm) and the last frame (zoom = 105mm). I think the first is slightly underexposed and the last is definitly overexposed. To my eye, the optimal exposure happened when the head was zoomed to 50mm. Again, for these demo pix, the only thing that is changing from frame to frame is the zoom setting. In a real shoot, I would have first found the vignette that I wanted and then dialed the power up or down.

Creating Vignettes

There is nothing that says you should not take the Speedlite out of Auto Zoom (by pressing the ZOOM so that  the zoom display blinks and then turning the dial). More often than not I will use a Speedlite in Manual Zoom and zoom it much tighter than the lens I am shooting. I do this intentionally to create a vignette and, by doing so, send the viewer’s eye to what I want him to concentrate on.

ZOOM = 24mm

ZOOM = 28mm

ZOOM = 35mm

ZOOM = 50mm

ZOOM = 70mm

ZOOM = 80mm

ZOOM = 105mm

ZOOM’s Power Hit

After shooting the above series and seeing the difference in light on Tony’s face and hand at each zoom setting, I set up a test to measure the amount of the light loss. In doing so, I resurrected my trusty Minolta Flashmeter IVF from the dark recesses of my camera bag (where I’ve kept it for years, largely for sentimental reasons).

I ran two series of measurements—one with the flashhead 24″ from the dome of the flashmeter and one with the flashead 48″ from the dome of the flashmeter. (There was, at most, a 0.1-stop difference.)

To keep the everything constant (other than the Zoom setting), I mounted the 580EX to a an off-camera E-TTL cord and then to a light stand and adjusted the height to the distances indicated. The flashmeter was set on the floor. I fired the Speedlite in Manual mode with the power dialed to 1/1. The flashmeter was set to ‘Non-cord Flash’. In this mode, it waits for a burst of light to take a measurement. The ambient light was not a factor.

So, using the output of 105mm as a baseline, here is the power lost at each ZOOM increment. The results are expressed as EV (exposure value). One EV is one-stop. I have separated them into the most relevant divisions (meaning that there is essentially no difference between 80mm and 70mm or between 28mm and 24mm).

105mm = Baseline

80mm = -0.1EV
70mm = -0.2EV

50mm = -0.6EV

35mm = -1.0EV

28mm = -1.5EV
24mm = -1.5EV

14mm = -2.9EV*

*14mm is achieved by pulling out the flip-down Wide-Angle Panel on a 580EX/EXII

Re-thinking the Wide-Angle Panel As A Viable Mod

ZOOM = 14mm (via flip-down Wide-Angle Panel)

I have to confess that I never considered the light lost by pulling out that little plastic Wide-Angle Panel at the top of a 580EX/EX II… until I shot these demo pix. Then, to measure it at nearly 3-stops, well I thought about breaking that sucker right out of my Speedlite. A 3-stop loss is even more than the power hit that comes from switching into High-Speed Sync (which I recently calc’d to be 2.5 stops—details to come soon). Just to be fair, after measuring the Wide-Angle Panel, I parked it back in it’s garage and popped a StoFen Omni-Bounce on the front. The light lost through this translucent white plastic cap was 2.6 stops—still a sizable hit, but less than the Wide-Angle Panel .

 

11 Responses to Consider ZOOM To Be A Speedlite Modifier

  1. hfng says:

    This info is really useful to know. Thanks for testing it out. Mostly use between 28 – 50mm with a shoot thru umbrella. Do you have any test results how much light is lost through an umbrella?

  2. Sometimes I want to use 14mm zoom so I just barely pull out the wide angle flipper which is enough to trigger the 14mm range. I never pull it out all the way so it flips down.

    • Syl Arena says:

      Kerry – I think all this does is move the flashtube to the 24mm position. It's my understanding that the only diff between 14mm and 24mm is the prisms on the flip-down panel. I have to shoot all the light patterns for the 'Speedliter's Handbook.' I'll add this to the list to verify either way. Thx. for sharing the thought.

  3. Spike says:

    Whoa – serious light loss with the diffuser on a 580ex. Very, very worthwhile being aware of that overlooked fact. Thanks Syl. This site is turning into the perfect partner to Strobist for us Canon shooters,

  4. Thanks for another great post Syl! Loved the two prior posts as well.

    Just a few weeks ago I played with several speedlites, shooting through a window to generate interesting shadows on my model, and toyed with the zooms on the speedlites. No light modifiers beyond 1/4 CTO gels. And you're right on, you really can use the flash zoom as a light modifier.

    Enjoying the new site, and looking forward to you upcoming book release!

  5. [...] Consider ZOOM To Be A Speedlite Modifier [...]

  6. […] tele. Por que es cuando la luz del flash va a llegar más lejos. A ver, un flash no “pierde potencia” según variamos el zoom (el resto del artículo es muy bueno). Si ponemos el flash a […]

  7. […] shots. Note how the shadows of the rock in Figure 2 allow you to see the texture of the surface. (See this article for more insight on using Zoom as a creative […]

  8. Mike Dree says:

    I lost the wide panel on my 580ex. Does it affect the perform of the flash?

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