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

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    \$\begingroup\$ I would get slightly worried about the shiny pins in optical path, hopefully it will not cause much troubles. \$\endgroup\$
    – ssavec
    Nov 7, 2013 at 6:27
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    \$\begingroup\$ The shiny pins inside are for electronics, so that aperture and autofocus still work. \$\endgroup\$
    – jean
    Nov 7, 2013 at 11:41
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    \$\begingroup\$ 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. \$\endgroup\$
    – JohannesD
    Nov 7, 2013 at 14:54

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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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  • \$\begingroup\$ 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. \$\endgroup\$
    – jean
    Nov 7, 2013 at 11:50
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    \$\begingroup\$ @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. \$\endgroup\$
    – AJ Henderson ♦
    Nov 7, 2013 at 13:59
  • \$\begingroup\$ @AJHenderson in that picture, it actually looks like five pieces - a body mount, three tubes, and a lens mount. Parts The numbered parts then are threaded to screw into each other (look closely at the top of the '3' in the lower right image). This makes for a simple design that can be reused for multiple lens mounts (just changing two pieces). \$\endgroup\$
    – user13451
    Oct 24, 2014 at 23:24
  • \$\begingroup\$ @MichaelT - took a second for me to figure out you meant the one jean was referring to in the comment. Yeah, I was just referring to the knob that latches the lens in to place on the lens plate. That's the same role as the push down things in the image on the original post. I agree that it is a vastly different construction for the comment one. \$\endgroup\$
    – AJ Henderson ♦
    Oct 24, 2014 at 23:33
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Don't fit your lenses to the extension tubes and then to the camera, unless the manual for the tubes says so. I use a Sony SLT-a77 with extension tubes and the instructions are to fit the tubes to the body first or the TTL and AE may not work.

I definitely wouldn't use tubes that have exposed metal inside the tube, like those pictured above. The insides of the tubes should be matte black with no light colours or shiny bits. The connections should be housed within the barrel and inaccessible without smashing the tube.

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