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FEL meter - using the flash meter inside your E-TTL camera

by Julian Loke

Contents

Introduction

"You need a flash meter". This is standard advice when setting up strobe lighting, particularly when trying to achieve shadows and highlights that conveys a sense of depth in a two-dimensional photograph. Flash meters can be expensive, and may misread the preflashes used for E-TTL synchronization signals.

Did you know that your E-TTL camera has a built-in flash meter? The readings are used for determining E-TTL automatic flash exposure. On high and top market models, such as the EOS 3 and EOS 1V, it is even possible to measure the flash exposure from manual-power EX series flash. Alas, this feature is not available on lower model cameras such as the Elan 7E. This document describes how to misuse FEL on any E-TTL capable camera to take manual readings of flash exposure.

Method

  • Set your camera to Av or M mode. Select the narrowest aperture possible with your lens.
  • Set your flash to E-TTL mode. If your camera and flash do not have E-TTL, this method will NOT work.
  • Aim your camera so that the flash metering segment covers a middle-toned area on your subject, or a photographic greycard.
  • Push the FEL button. You have 16 seconds to complete metering before having to FEL again.
  • Check in the viewfinder for a blinking flash indicator that warns of flash underexposure. If the indicator does not blink, try again with a neutral density filter (e.g. polarizer=2stops) and factor this into the final reading.
  • Adjust the aperture dial until the flash icon glows steadily, indicating adequate flash exposure.
  • This is the aperture reading for full-power flash.

Power ranger

Once you have found the full-power reading, adjust the aperture in one-stop steps to determine the settings for 1/2 power, 1/4 power, 1/8 power, etc. Knowing that EX Speedlites can only choke their power back by only seven or eight stops, you can accurately determine whether your selected aperture is within the flash coupling range, otherwise you risk flash overexposure. Should this be the case, either increase the flash-to-subject distance, or weaken the flash by bouncing, diffusing, or switching the flash to High Speed Sync (HSS) mode. You can also switch to a less sensitive ISO/ASA, or even apply a Neutral Density or Circular Polarizer in front of the lens.

Revision History

v0.1b2004Jan04 jul: EOS 3 & 1V
v0.1 2003Nov30 jul: Original draft

Comments

Thanks but I try to understand.
1. "try again with a neutral density filter (e.g. polarizer=2stops) and factor this into the final reading." if I just don't want to bother filters what shall I do?
2. the principle seems to be: start from under exposure until the light goes off; then reduce GN to see whether it is max. Instead you can also manual set the GN based on 1st step.
4. yet why we need that? for ex flash we can just press the shutter; for flashes sync how can we get rid of the preflash caused problem? Or the author's point is just tell us there is a meter?
lastguy 2007Feb05 11:14:16 -1000

1. The context in which the ND filter was suggested is where the flash is far too powerful to meter accurately.
This kind of situation occurs where you are metering
the reflection of the flash in a mirror at arms length.
You might actually need this kind of power if you are
shooting a high key image.

2. The suggestion to use Guide Number for calculations is fine, so long as your flash only has one Guide Number. My Canon Speedlites have a different guide number for different zoom settings, and also when using High Speed Sync (HSS)

4. This article was originally written about E-TTL and a film camera. E-TTL and EX flash is not very reliable. Although there is a system to warn against flash underexposure, there is no automated method to check for flash OVERexposure. Alas, this situation has not changed with E-TTL II. Fortunately, it is easier to preview the exposure on a digital camera than it was with film.
Julian Loke 2007Feb07 17:15:32 -1000


© 2004 Jan 04 Julian Loke for EOS Documentation Project. All Rights Reserved.

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