Stuck Tubes - Help !

Hey, I like the deliberating and discussions! That's part of all the fun for me ... I mean, if I get these things working, well, then there's nothing else to do other than use it all to take some actual photographs ....

It sounds like a plan to me.

Andrew

If, as Nigel says,

"
When the lens is not fully engaged onto the tubes there is some movement of the aperture, but not when fully locked in place"

there's something wrong with the stop-down lever in the tube. Most are spring-return, but some aren't and it's possible (tho difficult) then to get the len's lever engaged to the wrong side of the coupling.

Nigel, can you confirm whether both the couplings (stop-down and aperture transmission) are free to move in all these tubes?

+1 for the paint, have the same set and had to get the emery paper out. of course you have to have the aperture stopped down to see it work when you press the green button

Good question... Each tube has two levers, one short one long. The long one is connected to a spring running around half the diameter at the camera end. This long lever is pulled back to one side by the spring. The other small lever has no spring and just moves freely. This is the one that I found altered the ability to change the aperture when the lens was attached to the tube. Both levers on all tubes move freely and the springs work fine, nothing to suggest there is anything wrong with the tubes. I will try and scrape the paint around where the mount contacts are.

But I think that the small lever is being moved into the position that prevents aperture operation when mounted on the camera. Is it the case that having the contacts cleared of the paint will mean the lever will be moved into the other position when using the green button and firing the shutter, so allowing the lens to stop down at the same moment?

the small lever historically transmitted aperture setting from lens to camera. It should follow the similar lever on the lens and not impede it. It engages with nothing in the camera nowadays.

The longer one was previously only to allow the lens to stop-down (to the physically selected f-no on the lens), but on these later bodies it's also used to actually drive the iris to it's selected setting. You should be able to toggle the fitted lens open/closed with it.

Nigel this is the area that has to be cleaned off on each tube

Thanks! I'll try that over the next couple of days, and see if I can match that up with the tubes I've got. I'm guessing it has to take away the paint that covers a specific contact on the lens mount. Thanks to everyone who has helped so much, I'm actually very much enjoying messing about with the tubes and lenses, its all been a great new experience, and hopefully will open up many more photographic potential to come.

I have a set of Marumi K-A extension tubes and I had to scrape of the Anodizing on the bottom bayonet part. Anodizing is a very good insulator and it made the trouble. Once this was done the auto-diaphragm on my A lenses worked OK.

For the non Auto K extension tubes, there are quite often original Pentax K tubes on Ebay. I just bought a set of 3 rings for about 40 Dollars.
I do not recommend the Chinese made rings. They consist of 5 parts.
3 Rings and a male and female bayonet part.
I have bought some of them; and unless you have a lathe and know how to machine them for a proper fit. Don't buy them. They are cheap in price and cheaply made. You get only what you pay for.
I speak from experience.

Regards, Horst

Thanks, the Neewel brand ones I also have are in 5 parts, and the fit onto the camera and lens is not so precise and they are thinner and cheaper in feel. They do have the advantage though of allowing the aperture to be set !

It's no use trying to reason gently with machinery. Physical violence is the only effective measure.

Martin

Absolutely .......... http://web.aanet.com.au/bayling/repair.html

Andrew

What a hoot! Very Australian

Martin