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Almost every extension tube with electronics has them. What are they for?

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I would get slightly worried about the shiny pins in optical path, hopefully it will not cause much troubles. –  ssavec Nov 7 '13 at 6:27
The shiny pins inside are for electronics, so that aperture and autofocus still work. –  jean Nov 7 '13 at 11:41
I think @ssavec's point was that those pins might reflect incoming light to places where it shouldn't end up. There's a reason lenses are painted black inside. –  JohannesD Nov 7 '13 at 14:54
@JohannesD a valid point. Thanks for clarifying! –  jean Nov 7 '13 at 17:56

1 Answer 1

up vote 9 down vote accepted

They are so you can detach the lens. The lens latches in place on it and you push the button to allow it to be removed. This is the same function as the lens release on your camera.

When you go to put the tube on your camera you should attach the lens to the tube and then the assembly to the camera. When you are removing it, you reverse the process. Push the lens release on the camera, remove the entire assembly. Then push the button on the extension tube so that you can remove the lens.

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Thanks. It seems like a stupid question, but extension tubes without electronic pins inside don't have the detach hooks or buttons! :puzzled: Probably because they get screwed on like filters. –  jean Nov 7 '13 at 11:50
@jeancaffou - that little knob serves the same purpose in those ones you linked as not having a button. It looks like in that design it may pull out rather than push in, but it is just different designs for doing the same thing. –  AJ Henderson Nov 7 '13 at 13:59

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