Stuck Tubes - Help !

But these lenses have an aperture ring, and are not set to 'A', so there's no electronics involved. I can turn the aperture rings but there's no effect when they are attached to these tubes. Removing the tubes and attaching the lens to the camera directly restores full control of the aperture from the lens aperture ring, including 'A' setting control from the camera e-dial in the case of the 'A' 28mm.

I don't understand why the bayonet lever on the lenses is being moved over and pulling the apertures wide open when attached to the tubes?

Nigel, let's try a bit of fault finding .......

Fit your M75-150 zoom onto your K7, set the aperture ring on the lens to f/22. Switch on the K7. Set the exposure mode on your K7 to 'M'. Does the M75-150 stop down when you press the green button (look through the camera viewfinder)?

What happens if you fit one (or any combination) of the Jessop tubes to the M75-150 and press the green button?

Andrew

Let's make sure I understand what you are saying here. Are you saying that you can fit your M75-150 to any one of the Jessop tubes (but not to the camera) and, when you look through the tube, the lens aperture is always wide open, irrespective of the setting of the aperture ring??

ANdrew

Hi Andrew, to clarify those specific questions ... firsty about lens on camera only - with no tubes, and lens directly on camera, I have full control of the aperture with the lens aperture ring, plus I have correct stop-down metering (press green button in M mode, little pzziz noise, lens stops down and shutter speed is set) - all normal.

Now with the tubes on, any tube or combination of the 3 ... with the Tamron Adaptall auto-diaphram switch in 'manual', I have full control of aperture with the aperture ring, and I also have normal stop-down metering as described above.

Withe the tubes (any combination) and either the Pentax 'a' 28mm or 'm' 75-150 then the aperture ring on the lens has no effect - it does not change the brightness in the viewfinder, and there is no stop-down metering (no pzziz noise) - and the aperture remains fixed at full open. With the tubes and lens in my hand looking through, moving the aperture ring does not close the aperture in the lens - it remains fully open even at f22. Mystery?

Nigel

The simple answer to this is that you need to scrape off some of the paint finish where the tubes meet the camera body. Until you do this you will find the aperture does not stop down when taking the shot.

Regards
David

On the face of it, the difference is that you have the choice of switching to manual diaphragm on the Adaptall mount. There's no such choice on a Pentax lens.

There is however such a choice on Pentax M42 screw thread lenses, and perhaps these would help as an alternative. There are some amazing screw thread lenses.

I've just checked another set of Jessop tubes with my own M75-150 and that doesn't happen. The lens aperture behaves as you would expect. I have used the tubes that I sent to you with the same M75-150 and they also worked fine - but they've been in a camera bag and not seen daylight for a year or more since then.

A mystery? Yes, I simply cannot explain it.

You have my apologies. It would seem that I have sent you some faulty tubes. Deposit them in the bin and I'll send you some folding drinks vouchers in the post - or alternatively you could send them back to me (I'll refund your postage too)

Andrew

My memory may be faulty, David, but I think those tubes have an unpainted metalic mount. From Nigel's description of what happens mechanically, with a lens/tube combination not mounted to the camera - I can only conclude that they are faulty.

Andrew

But surely not all three in exactly the same way Andrew .. Could they all individually develop the same fault? Seems unlikely surely? The drinks vouchers can stay where they are, its worth it just for the learning and experimenting ... None of this would be anywhere near as much fun if I was actually able to take any photos with them!

Well, you have a point. The thing I really cannot wrap my head around is that I have used those tubes to take photos with a M75-150 and with a Pentax M 50mm f/1.7 - and I'm pretty sure they worked fine.

David is quite correct, you cannot use stop down metering (or catch-in focus) with a manual lens (or extension tube) that has a painted mount. You have to remove paint from the mount in the same area that the electrical contacts would be in an 'A' lens, until you see shiny metal. I have to do that with a (very good) Chinon 28mm f/2.8 macro lens. Remind me, do the tubes have a shiny metallic mount at both ends?

Andrew

They have a black paint same as the tube body on the camera mount end - and a silver colour (like a standard lens metal mount) on the lens attaching end.

Actually, now you mention it, I have to say that on the Tamron (which does give me aperture control with the switch in Manual), the stop down metering is a bit inconsistent - sometimes it doesn't work well - I've had to judge the shutter speeds mentally after changing aperture sometimes.

Oh ....... that just might point to the solution. You do need to remove some paint from the tubes so that they short the pins on your camera. You would need to do it on all the tubes. The issue is that if the lens/tubes do not short the pins on the camera, the camera does not know that it has a lens attached, so takes no notice when you press the green button.

You can prove or disprove that notion by cutting a little tinfoil and finding a way to attach it to the correct part of the tube before mounting it on the camera. If you suddenly get stop down metering working, then you know that you have a job to do with some light abrasive paper. Obviously, you would need to take great care to clean the tubes and not get any abrasive anywhere it shouldn't be.

It's a while since I used those tubes and, if they have a painted mount, I couldn't possibly have used stop down metering. Maybe I just guessed or maybe metered on Av (wide open) and calculated the correct shutter speed after setting setting the lens aperture ring.

Andrew

Well, my memory was faulty. I might also have been guilty of making an erroneous assumpton about how the tubes are supposed to work mechanically.

Let's hope that Nigel is on the way to a solution.

Andrew

Thanks to everyone for your input - the point about the contacts and paint needs to be investigated further - one thing I can report is that I tried the 'a' 28mm with a tube attached, but not on the camera , just in my hand - now when I move the tube bayonet to one side then the lens aperture WILL adjust in accordance with the ring position - but with the tube bayonet moved to the other position then I lose the aperture control.

So it seems that when the tube is mounted on the camera that this bayonet is being moved into the position that holds the aperture wide open (this is for normal metering operations isn't it?) - something is stopping it from moving to the other position when mounted on the camera?? Is this to do with the contacts matter?

It's definitely the paint Nigel, it doesn't need investigation, it's the paint that's doing it! Just remove some with a scraper, or with a dremel type tool, you can't harm the tubes doing this as there's nothing to damage, just do it man and stop deliberating over it!!

Cheers
David