extension tubes

Now that's very interesting.

7 actual contacts, and the paint-scrape modification. Did it already have the latter, or did you do it?

Look at my Jessop tube - only 6 contacts, and the paint-scrape mod was needed for aperture information to get through.

[IMG]http://i162.photobucket.com/albums/t244/chris5gd/Technical/Imgp2649s-1.jpg[/IMG]

I have those ones too, I discovered them in their box in another box in a cupboard in the garage, used once around 1990 and forgotten about. I have yet to carry out the paint scrape mod. Why/how does it work?

I'm not entirely sure.

There's no paint on the lens side of the tubes, though, so with the scrapes in place, the contact on the body can get all the way through to the lens.

What I don't understand at all, though, is why you'd need the scrape if there was already a seventh contact. There's no eighth contact on the body.

If the camera/lens electronics relies on electrical continuity between the K flange on both body and lens irrespective of any other contacts (perhaps as a common ground/earth/return - whatever you want to call it), painted/insulated tubes would need the paint/insulation to be scraped off to achieve that continuity, and it wouldn't matter where it was scraped from, just that it was of sufficient area to achieve a reliable connection.

So, maybe a bit like 4p flash having three contacts and 5p having four, the body itself is a conductor?

Think Peter just summed it up quite well, it was weird, they worked fine with my DA*'s, but wouldn't work with the Tamron 90mm Macro, there was a post in the troubleshooting section somewhere!

Found it!
link

Hi Roy

I have a set of Jessops tubes with the contacts, I forgot to put them on my list in the classified, will let them go for £25.00. I think they also might need the paint scraped like what Unlocker has done though, they worked great on the *istD, but I haven't used them much with the K10D.

I paid about £30 for mine, and they DO have the electrical contacts, (they are Jessops incidently) I reckon £30 for yours was a bit excessive although if Unlocker has paid £60 for his then I must have got a bargain.

PS: I see Unlocker has also had to scrape off some paint to get them to work

WHOOPS Sorry folks, I managed to reply without realising there was a second page of replies, so missed all the fun re-contacts and paint removal, I found McBrians reply interesting, I had to scrape the paint to get mine to work on my istD, I remember I got the advice on this forum, from Mannesty if my memory serves me right.

You can still rely on your memory, you are correct. I think I was the first here to discover what (I thought ) the problem was, and the fix.

I thought, that I needed to scrape paint from where the additional contact should be. I'm pretty sure now that the paint can be scraped from anywhere on the mount face to create the required electrical continuity between lens mount & body mount.