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Blank FEL - How to sync studio strobes with an E-TTL-only camera

by Julian Loke

Contents

Introduction

Most studio strobes accept either a PC (Prontor-Compur) sync cord connection, or may be set to synchronize to a single flash pulse by using an optical sensor. However the E-TTL system uses preflashes, both for metering to determine the correct flash exposure, and also to signal other E-TTL flash units. A studio strobe on an optical slave trigger would be triggered prematurely by the E-TTL preflashes, and may not synchronize correctly.

With a film camera, such as an EOS-1v, you can eliminate the pre-flash by forcing 'TTL' mode on the flash. You can either set the appropriate custom function on the flash unit, or insulate the hotshoe (see: EX-M-TTL). Digital EOS SLR users have to use flash set to manual power mode, since TTL flash is totally incompatible with new digital SLRs. It seems wasteful to buy a dedicated manual flash just to use as a strobe trigger.

This document details a simple method that can be used to synchronize optically triggered studio slaves to your E-TTL-only camera without using any additional equipment. You can even make use of a built-in popup flash!

Method

Dark Method

Use this method if your master flash should NOT add light to the scene.

  • Power up your strobes and camera.
  • Use an E-TTL flash in standard mode (i.e., neither wireless master nor slave). The popup flash on a digital SLR is fine.
  • Filter the flash with an infrared filter made from processed unfogged slide film.
  • When you are ready to shoot a picture, cover the flash completely (e.g. with your hand, some metal foil, a changing bag or even a dark cloth)
  • Push and release the Flash Exposure Lock (FEL) button. The E-TTL preflash will be emitted, but should not trigger the slave strobes.
  • You now have 16 seconds to shoot your picture.
  • Uncover the flash, and depress the shutter button fully to take the picture.

Light Method

Use this method if you intend the master flash to light the scene.

  • Power up your strobes and camera.
  • Use an E-TTL flash in standard mode (i.e., neither wireless master nor slave). The popup flash on a digital SLR is fine.
  • Push the Flash Exposure Lock (FEL) button. The E-TTL preflash will be emitted, and will also trigger the slave strobes.
  • Press and hold the FEL button a second time. This time, the slave strobes are recharging and should not interfere with the E-TTL metering.
  • Continue to hold the FEL button for the few seconds while the strobes finish recharging.
  • When the strobes have recharged, release the FEL button.
  • The camera retains the FEL reading for 16 seconds. Shoot your picture before it times out.
  • Depress the shutter button fully to take the picture.

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How it works

This technique is called "blank FEL" since the E-TTL preflash is fired blank, well before the shutter opens. When you shoot the picture, only the second E-TTL flash is emitted, triggering the studio strobes correctly.

Be careful that under wireless flash conditions, E-TTL emits more than one preflash. If this is the case, the method will fail. So be sure to proof check your results before committing to an important shoot.

Alternatives

Other solutions do exist. You could mount a simple manual flash (such as a Sunpak 383 Super or a Vivitar 283 or 285), either on the hotshoe or synchroized via a PC cord. Be careful not to exceed a safe voltage for hotshoe mounted flash. See: Strobe Volts website.

Another method is to plug "digital-ready" optical slave triggers into your strobes so that they trigger on the second or third (or fourth) flash. Some advanced units can be trained to cope with different number or preflashes from different equipment.

An even more expensive, but more reliable solution, is to upgrade to a radio triggering system.

Revision History

v0.2 2004Sep25 jul: Double FEL for Light Method
v0.1 2003Nov23 jul: Original draft; jc: edits; redo intro; jul: dark & light; reworked text; edits

Comments

If you have a 550ex or sigma 500 super then you could do what I use for studio/location shoots, switch the flash to manual, drop the power to 1/32 or whatever, put the head in bounce position and shoot away, easier than FEL-wait-shoot.
Ben Rubinsetin 4/1/2004 11:06:56 PM

Thanks for the comments Ben.

As stated in the article, buying a 550EX or EF 500 Super just to trigger studio flash can get expensive. It might be cheaper to buy a cheap (but voltage safe) auto-thyristor flash. Or even a hotshoe-to-PC sync cord adapter.

The delay when using the dark method can be very minor. Cover the popup flash, push FEL, uncover the popup flash, and shoot. Mounting the camera on a camera support helps considerably.
Julian Loke 4/8/2004 6:14:37 AM

I agree with Ben using the 550ex in manual mode solves the problem. I find that setting the minimum power level of 1/128 is adequate for my storbe slaves.
Ted Coffey 11/10/2004 1:15:23 PM

The whole idea is to do this without any additional equipment. The technique can be used with just the popup flash on a midrange DSLR.
Julian Loke 12/9/2004 1:14:16 PM

This is a cool way to get by without any additional equipment.

Another idea that is cheaper than a hotshoe flash and less hassle than messing with FEL for each shot is just to plug a PC sync cord between the camera (my 20d has a socket next to the cable release socket) and the studio strobe. I haven't tried that but it should work fine for cameras that have the PC cord socket.
Tom Morrow 2005Jun23 16:12:54 -0700

I use a Sigma EF500DG Super and find that it can keep up the pre-flash and main flash at 1/16 power and below, fine for small portraits - for larger scenes or if I just need more light I use the FEL method.
Graham McCauley 2006Feb28 08:50:33 -0800

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© 2004 Sep 25 Julian Loke for EOS Documentation Project. All Rights Reserved.

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