what is inside a canon extension tube

[willg]

i know there is no glass, but is it just metal connectors to go from lens to camera or is there more to it...this guy took one apart and there was a chip inside...what is the purpose of that?
its not a canon, but i am willing to bet the canon has some circuitry in it too...would it not work with just connectors?

http://www.geocities.com/Yosemite/8917/tube.html

[robertwgross]

On some extension tubes, the signals from the camera go straight through the tube to the lens and vice versa. In other words, the tube is transparent to the data signals. In other tubes, the tube has the intelligence to make its presence known to the camera, and the extra stop of light loss by the tube is added into whatever the lens was telling.

---Bob Gross---

See below!

[willg]

so the ef 12 i just bought probably is the smart kind right?

[robertwgross]

Correction!

I mis-spoke. I was thinking about teleconverters.

Extension tubes are not the same.

Sorry.

---Bob Gross---

[Steve Parr]

Correction!

I mis-spoke. I was thinking about teleconverters.

Extension tubes are not the same.

Sorry.

---Bob Gross---

Dumb question time:

What's the difference?

Steve

[raylks]

Extension tube is just a tube without any glass inside attached between the lens and the camera body so that the minimum focusing distance of a lens can be reduced. A 12mm tube can shorten the min. focusing distance by 12mm, and the case is the same as in 25mm tube and 36mm tube.

It fits macro shooting well but in using the tube, you lose the focusing at infinity distance.

A extender or tele-extender is a group of glasses attached between the lens and teh camera body, so that the effective focal distance can be lengthened. A 1.4x converter can covert a 200mm telelens into 280mm but on the other hand, the aperture value is reduced by 1.4x.

Both devices will reduce the light entering into the camera so that exposure compensation is necessary (i.e. you need to make the exposure "brighter" to get a proper exposure). HOWEVER, most cameras now including Canon EOS have adopted TTL metering so that exposure compensation is NOT necessary when using these devices.

[ScottE]

What's inside a Canon extension tube looks exactly the same as what's inside a Kenko extension tube. To me it just looks like air, but it must be really good air because it costs more than twice as much as the air inside a Kenko tube.

Scott

p.s. Kind of reminds my of a girl I know whose garage wanted to charge her for putting fresh air in her tires. Not being dumb she refused to pay until they showed her the old air they took out.