What is the red window on 420EX flash for?

[bill.akstens]

I notice my 420EX has a red sensor window on it. Does this sensor

need to be aimed at my subject for proper exposure? I assume with my

ETTL (Elan IIe) body all flash exposure is determined through the

lens/camera, not the 420EX window. If this is true, the red window

must only be used for the focus-assist light and remote slave

communications with a 550EX master. So if I use the 420EX as my only

flash (off-camera with a handheld OCSC2) and I can focus without an

assist light, then it shouldn't matter which way the red window

points. Obviously it does matter which way the flash output is aimed,

but not the red window. Am I correct? Thanks!

[bill_goldman]

Yes, your analysis is correct.

[jbq]

Correct, it's only used for AF and IR comm, but not for metering.

[thomas_sullivan]

so.........you could use the 420ex and a Photoflex Convertible Umbrella, shooting THRU the White Satin (black backing removed of course) with the extension hotshoe cord thing..........and it would work ETTL wise?

[steve_dunn2]

<p>Actually, the master/slave sensor is under another window - the dark one above the AF assist beam cover and below the flash head.</p>

 

<p>As for what points where, you're right, and in fact in a master/slave setting, you may run into situations where you want the body of the flash facing a different direction from the head, so that the body is better able to receive signals from the master.</p>

[bill.akstens]

Given the above, I think the answer to Thomas' question is yes you could do that. You might need two cords tied together to get enough space for the diffuser, and you would not be able to rely on the focus assist light from the flash. But otherwise it should work OK. Power output would of course be significantly reduced, but for short distances would likely be OK.

[jbq]

Yes, E-TTL (in spite of what lots of people say about it) is able to get consistent exposures when not shooting straight with a naked bulb (although E-TTL II is able to get extra precision in that case). E-TTL meters consistently no matter what you put on the flash, i.e. it works if you have a bouncer, a filter, a diffuser, a beamer...