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I read at the photonotes website that the Canon 50mm f/1.4 USM lens does not return distance information to the camera, to be used for E-TTL II.

How important is this, and should this be a determining factor when purchasing a lens?

The reasoning behind distance information is somewhat vague and stated as:

Under certain conditions the distance data is factored into the calculations for determining proper flash output.

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I can't see it being important, no. Distance information might make flash metering more reliable, but it's not essential. However you have to ask why you'd be using a fast prime lens with direct flash in the first place. A wide aperture is useful when bouncing flash due to the loss in power, however when firing the flash directly you don't need the speed and so a zoom would be more useful. But the real advantage of an f/1.4 lens is the ability to shoot indoors without flash

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  • I was going to include a note about that in the original question, I know that a short prime isn't exactly the most typical pair to a strobe, but it was the only lens in the list I would consider owning. I think it is an issue with quite a few old lenses that haven't been upgraded since ETTL II came out. Maybe it is a moot point as you suggest, since bouncing is much more likely, and distance info isn't use in that case. – dpollitt Dec 29 '11 at 22:57
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No, it is not important. The 50/1.4 lens does just fine with flash.

That said, it's the only lens I have that I would not buy again. I've had trouble occasionally with it deciding not to autofocus. Apparently, that's a design flaw with this particular model. I no longer use it on gigs because I don't trust it.

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