Problem with RB67 140mm C lens shutter release on extension tubes

[Drizzt321]

So, I've recently tried to go into macro photography with my RB67 Pro-S, got the 140mm macro lens, got the extension tubes #1 & 2. Tested out the lens when I got it, works fine directly mounted, including with shutter release cable. Added on the #1 and #2, and things get iffy. Sometimes it the shutter is released, sometimes it is not. Especially with the cable release, and especially with both #1 & #2. After a bit of fiddling, it _appears_ that, when the shutter button on the body is pressed, even though the extension tube mechanical linkage moves all the way to the end of it's movement, it doesn't move the 2 prongs on the lens far enough to release the shutter. With the shutter release cable, for some reason it doesn't seem to push in far enough to hit the shutter button. If I use one of those tiny screwdrivers (jewlers/watchmaker/etc), then I can push in far enough to hit the shutter release and it goes.

Did I get a dud lens? Is there something internally I could adjust or replace a spring or something? Or should I try and find a reasonably priced 2nd copy?

 

[MattKing]

If the lens functions correctly without the extension tubes, I would suspect the tubes.

 

[Drizzt321]

The tubes work fine with my other lenses, plus I got another #2 and tried with just that, and still the same. It's strange.

 

[Alan Klein]

Although I don't have the tubes, the manual says that when you initially mount the lens to the extension tube, cock them both. See page 26 and 27.

 

[Alan Klein]