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Most of Canon Speedlites flashes have quite nice built-in AF-assist LED lights, which would are useful in low-light situations, even when one doesn't want to use flash in photos.

Is there any way to set the flash (or camera) to fire only AF-assist, and not the flash itself? Only way I know is to prefocus and then turn off the flash, which is not very practical.

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Same questionf or Nikon: – mattdm Mar 23 '11 at 3:16
up vote 14 down vote accepted

Disable the flash in the camera settings. It still uses the AF-assist beam, but it will not fire the flash.

The setting is in different places depending on the camera, for example:

Menu > Custom Functions > 07

EOS 5D mk II:
Menu > Tools 3 > External Speedlite control > Flash function settings > Flash firing

EOS 550D / Rebel T2i / Kiss X4: Menu > Camera 1 > Flash control > Flash firing (it also works for built-in flash)

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Thanks! Does the Mk II variant also work with non-recent models like 550EX or 580EX? I thought that camera-flash control was limited to 580EX II and 430EX II. – che Jul 20 '10 at 15:35
@che: Yes, I have a 550EX, and it works. Some of the settings only work with newer flashes, but disabling the flash works with older ones also. – Guffa Jul 20 '10 at 15:36
You can't disable the flash and still have the AF assist lamp on the older 1 series Canons (1DmkI&II, 1Ds mkI&II) which is very annoying... – Matt Grum Oct 28 '10 at 15:34
@Matt Grum: That's an odd limitation... Even my old D60 can do that. :P – Guffa Oct 28 '10 at 18:49

Generally this can be enabled through a custom function on your camera -- depending on your camera, the setting will be in a different place.

In low light situations, the flash may still strobe to assist in metering and determine how much flash power is required.

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In camera's custom functions I've only found setting to enable/disable AF-assist beam, not having only the AF-assist :/ – che Jul 20 '10 at 12:26

EOS 5D (mk1) and 580EX II AF-assist & no flash:

  1. EOS 5D: {CF7: 1 (=flash off)} & {CF5: 0 (=send)}
  2. 580EXII: {CF8: 0 (Af-assist light on}
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Use an ST-E2. It has a focus assist lamp but no flash head. :)

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