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05-30-2020, 12:39 PM   #1
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K-1 with M-Lenses and Auto Extension Tube

I want to use an M-Series 100mm macro with a Vivitar extension tube. The extension tube is K-compatible with manual era auto couplings, and it works fine on an LX. It has no electrical connections. Also, the 100mm macro works as expected on the K-1, ie in M mode the green button sets the exposure, the aperture stops down for the picture, and the optical Depth-of-Field pre-view works from the 3rd position of the ON-OFF lever.

However, on using the extension tube with the 100mm macro (or any other M-Seris lens I have), the camera and lens do not respond either to the green button or to the D-o-F lever. I can take a picture but the aperture remains fully open.

The Vivitar extension tube's inner coupling face (ie to the camera) is painted black, or maybe has some anodising treatment that makes it black. I did read somwhere that paint can cause loss of function, but I I would have thought that applies to lenses with electronic functions, and my set-up is purely mechanical. I am reluctant to scrape paint off an otherwise mint tube unless I am sure it will be a solution. Alternatively I could dismantle and remove the auto linkage from the extension tube and use the lens like a pre-set.

Can anyone confirm that the paint is the problem?


Last edited by Lord Lucan; 05-30-2020 at 12:39 PM. Reason: Format
05-30-2020, 12:56 PM   #2
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QuoteOriginally posted by Lord Lucan Quote
The Vivitar extension tube's inner coupling face (ie to the camera) is painted black, or maybe has some anodising treatment that makes it black. I did read somwhere that paint can cause loss of function, but I I would have thought that applies to lenses with electronic functions, and my set-up is purely mechanical. I am reluctant to scrape paint off an otherwise mint tube unless I am sure it will be a solution. Alternatively I could dismantle and remove the auto linkage from the extension tube and use the lens like a pre-set.

Can anyone confirm that the paint is the problem?
I believe for the stop-down metering (or stopping down M lenses at all) to work, the lens mount needs to be conductive... you can do this by scraping off the paint.
05-30-2020, 01:45 PM   #3
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QuoteOriginally posted by Lord Lucan Quote
Can anyone confirm that the paint is the problem?
Yes it is the problem. I had the same issue with my Kenko branded extension tubes.
The good news is, you don't have to remove the whole paint, just a tiny area (where the pin of the camera mount is checking for conductivity (the lowest pin with the slight gold stain))
If you are not sure where exactly, you can test the position by sticking aluminium foil between the camera and extension tubes when mounting.
05-30-2020, 03:49 PM   #4
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I made a thread about this a couple of weeks ago. the solution is fairly simple.
KENKO 12mm Macro Extension Tube - Aperture not actuating on digital cameras? - PentaxForums.com
If you want guidance on where to scratch the paint, check the ground contacts on a DA L lens, the ones with the plastic mount.

05-30-2020, 04:12 PM   #5
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Thanks for that guys, and I had not seen the thread about the same problem with the Kenko tubes - so many sub-forums here!

Good idea about using metal foil to confirm it's the problem, and I will take the paint off after that. It's midnight here now, so I will experiment tomorrow.
05-30-2020, 08:36 PM   #6
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QuoteOriginally posted by Lord Lucan Quote
Thanks for that guys, and I had not seen the thread about the same problem with the Kenko tubes - so many sub-forums here!

Good idea about using metal foil to confirm it's the problem, and I will take the paint off after that. It's midnight here now, so I will experiment tomorrow.
1/4” copper foil tape from Amazon (USA).
05-31-2020, 03:28 PM   #7
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Well, I've done a test by sandwiching some alum foil between the extension tube and the camera body in the area of the contacts, and it did enble the green button etc to function

But looking for a permanent solution, I gather from other PF threads and resources that the "Data Pin" (which seems to be the 7th pin) on the camera needs to make electrical contact with the body of the tube or lens. For example in MarcusBMG's review of a similar jessops tube in :

Jessops Auto Extension Tubes PK-A reviews - Pentax Camera Accessory Review Database

... he says "I moved on to scraping the anodising off where the 7th data contact is and that had the desired result" . The seventh data contact is the one marked "v" (confusingly a Roman 5) in this view of a KAF lens mount from the article The Evolution of the Pentax K-mount - Articles and Tips | PentaxForums.com , which it calls the Digital information contact

What concerns me is that making one electrical contact cannot be enough, two are surely needed to make a circuit. The article and picture below identify the contact number 2 (the one which is a small copper plate in the plastic mount shown) as the earthing contact. So I'm guessing that, if any paint scraping is to be done, it would have to be for both contact numbers 2 and 7.





05-31-2020, 03:37 PM   #8
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QuoteOriginally posted by Lord Lucan Quote
The article and picture below identify the contact number 2 (the one which is a small copper plate in the plastic mount shown) as the earthing contact. So I'm guessing that, if any paint scraping is to be done, it would have to be for both contact numbers 2 and 7.
No, pin number seven (or V in the picture) was enough for my tubes to work.

06-06-2020, 05:41 AM   #9
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I've got back to doing this job and here is the rest of the story, with a happy ending

As two connections to the lens are needed to complete a circuit, in the cases of those who have found that ensuring the Data Pin 7 makes a connection to the lens is sufficient for the lens to be detected, I believe that the other connection must have been via the lens body to the camera body ("earth") in areas where the mount coating has worn sufficiently to bare metal to allow electricity to pass.

In my case however, the extension tubes, although sold as "used", looked as if they had never been used, and had no bare metal anywhere around the male mounts. The black surfaces of the mount must be some kind of anodising, not paint, and quite hard. I painstakingly scraped and filed a small area where Pin 7 touches, and for the earth I filed off the anodising behind one of the mounting claws; this cannot be seen in my photo. I removed the tube's mounting ring (four tiny crosshead (JIS ?) screws) while filing.

I have done this mod to only one of the set of three tubes, the thinnest. As long as this is fitted nearest to the camera body, the arrangement will remain functional with the other tubes mounted outboard of it. I think that should cover all use cases for me.

The photo shows the extension tube's male mounting ring with the bare contact patch for Pin 7 on the right. Having now dismantled and worked on it, I am impressed by the build quality of these Vivitar tubes.


Last edited by Lord Lucan; 06-06-2020 at 05:42 AM. Reason: Clarity
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