Problem with macro extension tubes and chosing aperture

I have just got a set of macro extension tubes (for Canon). The problem is that it is not possible to chose the aperture when one or several rings are attached to the lens, it is fixed at F00. See photo...

The electronic contact "points" are slightly different on the tubes than on the lenses (Canon lenses) and we suspect that might be the fault? Has anyone had the same problem?

The contact points look like the ones on my Kenko tubes I just got on the 23rd. Not sure what the issue is. I'm wondering if you are getting some kind of incomplete connection between the tube(s), lens, and camera?

How are your Kenko tubes working?

Lotta wrote in post #17832244
How are your Kenko tubes working?

I've only given them a quick function check on the night of the 23rd, and they functioned fine. I worked a long Christmas Eve night, and haven't had a chance to really test them yet, but funtion wise everything seems to work fine. What brand did you get? If you are having issues I'd try to return them.

Worked yesterday, but will look at it again today. The package has no brand name...

My Kenko tubes work fine. Lotta, I think your problem is that the units you got were made by the lowest bidder: not uncommon with cheap Chinese stuff.

If you're not ready to pony up the dough for Kenko tubes Neewer had a set that runs about $30 on amazon. I purchased a set and after exchanging the first set because they didn't work properly I've had good results from them. I used 3 of them stacked to help get this image.

at least they have the coveted red ring!

I purchased a very inexpensive tubes ($58 shipped) with electronic contacts from a vendor on eBay, and although folks can put ONE tube onnevertheless they lose contact with multiples stacked...Yet I can stack all three and still communicate with the lens as if none were there. My expeience does not solve your problem, but it does give you an idea of what is POSSIBLE, even with the expense of Kenko tubes.