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01-31-2015, 01:29 PM   #1
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Teleconverter Aperture Control Issues

Hi Pentax folks,

I have 3 teleconverters that seem to have problems with aperture control.


1. Vivitar MC Teleconverter 2X PK-A/R-PK

Despite being designed for the KA-mount, the teleconverter does not transmit aperture information to the camera (F-- is displayed with all lenses I tested with). I opened it up and found all 7 pins intact, I cleaned them with electrical contact cleaner spray but still no aperture information.


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2. Tokina Doubler for P/KA

The teleconverter transmits aperture information with most lenses correctly but with my Sigma 70-300mm APO DG Macro it makes the camera (K-5) display much lower aperture values: from 1.2 (instead of 4) to 5.6 (instead of 22). I tested it in M mode while setting the aperture on the lens and found that only the displayed apertures are off, the actual apertures are fine.


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3. Vivitar MC Teleconverter 3X-22

No matter what aperture I set on the lens, the teleconverter keeps the aperture wide open. I checked the aperture control lever and it seems to be ok.


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Any suggestions are welcome. Thanks in advance.

Tarnag

01-31-2015, 03:02 PM   #2
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I have a Kenko and it works perfectly, but I did notice it has 2 contacts inside and outside.
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01-31-2015, 03:19 PM   #3
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QuoteOriginally posted by Rimfiredude Quote
I have a Kenko and it works perfectly, but I did notice it has 2 contacts inside and outside.
That's the "Pz" part of the Kenko. They were originally used for power zoom but are now used for SDM. Without them, SDM lenses will not autofocus. If you're not using SDM lens, then they do nothing.
01-31-2015, 03:21 PM   #4
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Welcome to the Pentax Forums!

QuoteOriginally posted by tarnag Quote
1. Vivitar MC Teleconverter 2X PK-A/R-PK

Despite being designed for the KA-mount, the teleconverter does not transmit aperture information to the camera (F-- is displayed with all lenses I tested with). I opened it up and found all 7 pins intact, I cleaned them with electrical contact cleaner spray but still no aperture information.
The "A" contact is not being detected. This may be caused by poor contact between lens and TC as well as TC and camera. There is also the chance that there is a break in the wiring within the TC. Remember that a lens with "A" contacts must be mounted and the aperture ring (if any) must be in the "A" position.

QuoteOriginally posted by tarnag Quote
2. Tokina Doubler for P/KA

The teleconverter transmits aperture information with most lenses correctly but with my Sigma 70-300mm APO DG Macro it makes the camera (K-5) display much lower aperture values: from 1.2 (instead of 4) to 5.6 (instead of 22). I tested it in M mode while setting the aperture on the lens and found that only the displayed apertures are off, the actual apertures are fine.
Does the Sigma work properly when mounted directly to the camera?

I notice you said "most" lenses. I suspect that one or more of the pins may be "dead". For a map of the pin-outs and translation for aperture ranges, see Features and Operation of the Ka Mount

QuoteOriginally posted by tarnag Quote
3. Vivitar MC Teleconverter 3X-22

No matter what aperture I set on the lens, the teleconverter keeps the aperture wide open. I checked the aperture control lever and it seems to be ok.
The TC has a non-conductive base. This can cause problems with current model Pentax dSLRs. Try shorting across the data pin on your body (use foil) to see if that makes any difference.



Steve

01-31-2015, 03:34 PM   #5
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Check the pins with a continuity checker or multi-meter.

The Sigma may need a 7 pins on the TC to interact properly.
02-02-2015, 07:48 AM   #6
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Hi again,

Thanks for the suggestions.

Steve was right: with both Vivitars the problem was caused by the non-conducting mount of the teleconverter.

On the Vivitar 2x, I scraped down the black coating and now it transmits aperture information. However, it shows the same symptoms as the Tokina: it works fine with manual focus lenses but registers false apertures with autofocus lenses. I tested it with Pentax FA series, Pentax DA series, Sigma DG series and Sigma DC series lenses but all wrong.

With the Vivitar 3x-22, the whole mount is non-conducting (black anodized) so this is the reason the Green button does not stop down the aperture. As Steve suggested, I put some foil below the teleconverter mount to short the body contacts and this solved the problem. I will sand down the black coating later.

I took the Tokina teleconverter apart and found all 7 pins intact, I cleaned them with electrical contact cleaner spray but it still registers false aperture information with all autofocus lenses I tested with.

I found a similar issue reported with a Kenko 2X KAX Teleplus MC4 teleconverter here: Kenko 2X KAX Teleplus MC4 Lens Reviews - Miscellaneous Lenses - Pentax Lens Review Database

So it looks like that despite having electrical contacts for aperture information, these old teleconverters designed for the KA mount just do not work with contemporary lenses as they miss the extra contact of the KAF mount. This is very unfortunate as I bought these with a plan to remove the glass and use them as extension tubes for my Pentax DA lenses but now I have to guess the aperture.

There are some extenstion tubes on the market with electrical contacts but they have the same contacts as these teleconverters so I guess they will not work with autofocus lenses either. Does anyone have any experience with these?

I also have a Vivitar 2XMC7 AF teleconverter (same as the Kenko pictured above but without the SDM contacts) and it works perfectly with autofocus lenses too. But is was a little bit too expensive to take apart and use as an extension tube…

Any ideas and suggestions, please let me know. Thanks.
02-02-2015, 08:05 AM   #7
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QuoteOriginally posted by tarnag Quote
Steve was right: with both Vivitars the problem was caused by the non-conducting mount of the teleconverter.
Good call. Since the rear mount of the Vivitar 2x was not shown I had not noticed it was non-conductive. Some of the Pentax DSLR bodies need the 7th (data) pin shorted on the camera body in order for the green button and/or stop-down lever to work.

QuoteOriginally posted by tarnag Quote
I took the Tokina teleconverter apart and found all 7 pins intact, I cleaned them with electrical contact cleaner spray but it still registers false aperture information with all autofocus lenses I tested with.
Neither your Vivitar or Tokina TC only has six contacts for the Pentax mount. The seventh pin you have is the "Ricoh" pin and is not used by the Pentax KAF2 mount. The missing pin carries the digital information from chip (if any) in the lens. Compare the number and placement of pins to the TC that rimfiredude posted.

Refer to the link above in Stevebrot's post or
The Evolution of the Pentax K-mount - Articles and Tips | PentaxForums.com
02-02-2015, 08:41 AM   #8
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QuoteOriginally posted by tarnag Quote

I took the Tokina teleconverter apart and found all 7 pins intact, I cleaned them with electrical contact cleaner spray but it still registers false aperture information with all autofocus lenses I tested with.

I found a similar issue reported with a Kenko 2X KAX Teleplus MC4 teleconverter here: Kenko 2X KAX Teleplus MC4 Lens Reviews - Miscellaneous Lenses - Pentax Lens Review Database

So it looks like that despite having electrical contacts for aperture information, these old teleconverters designed for the KA mount just do not work with contemporary lenses as they miss the extra contact of the KAF mount. This is very unfortunate as I bought these with a plan to remove the glass and use them as extension tubes for my Pentax DA lenses but now I have to guess the aperture.

There are some extenstion tubes on the market with electrical contacts but they have the same contacts as these teleconverters so I guess they will not work with autofocus lenses either. Does anyone have any experience with these?

I also have a Vivitar 2XMC7 AF teleconverter (same as the Kenko pictured above but without the SDM contacts) and it works perfectly with autofocus lenses too. But is was a little bit too expensive to take apart and use as an extension tube…

Any ideas and suggestions, please let me know. Thanks.
when you say the teleconverters give the wrong aperture, what do you mean?

you mean that they feed the information direct through to the camera without considering the two stops of additional TC or they just feed "garbage" if they are straight through contacts you should see the native lens aperture.

02-02-2015, 01:15 PM   #9
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QuoteOriginally posted by tarnag Quote
On the Vivitar 2x, I scraped down the black coating and now it transmits aperture information. However, it shows the same symptoms as the Tokina: it works fine with manual focus lenses but registers false apertures with autofocus lenses.
This makes no sense. Your Viv 2x already has a conductive base and is designed for manual focus lenses with Max/Min aperture being communicated through the six contacts. This is the case regardless of whether a lens with the 7th data contact is present. That is why I asked whether your Sigma worked properly without the TC.

The Viv 3x does not have any contacts and should ALWAYS result in F--- being displayed on the LCD and will ALWAYS shoot wide open in other than M mode. It must also ALWAYS be used with a lens having an aperture ring. You can NEVER control the aperture from the body with this TC.


Steve
02-02-2015, 01:45 PM   #10
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QuoteOriginally posted by tarnag Quote
So it looks like that despite having electrical contacts for aperture information, these old teleconverters designed for the KA mount just do not work with contemporary lenses as they miss the extra contact of the KAF mount...
This is simply not true, at least according to available documentation regarding the 7th (data) pin. Base max/min aperture is not part of the data available. I use my AF lenses (including the Sigma 17-70 (c)) all the time on my Super Program film camera* with no problems. All current generation AF lenses are compatible with all k-mount cameras capable of setting aperture from the body, including those that lack the 7th pin.

If your TCs with contacts do not properly register the max/min aperture it is because either:
  • The contacts are not positioned properly to provide continuity
  • The lens is not mounted properly to mate contact to contact. This would include flexing of the mount due to lens weight or poor machining.
  • The wiring inside the TC is bad (broken wires and/or bad solder joints. A check with a continuity tester will help here.
This is not rocket science nor is any voodoo involved Edit: There is some Voodoo**. There is nothing magical that happens in the TC or with the 7th (data) pin that would make the lens/TC combo lack basic functionality. Edit: As noted below, there may be something magical happening, though what it is would required some investigation with a multi-meter or continuity tester to figure out.


Steve

* Predates the 7th (data) pin. Edit: I remembered wrong ...I don't use the Sigma on my Super Program, though it works fine with my Pentax DA lenses.

** The Sigma 17-70 (c) apparently does some form of voodoo since metering is totally wonked as well on the Super Program. My other Sigma (50/2.8 EX DG Macro) works fine with all my K-mount cameras (10+) from the KX (film) through the K-3. I suspect that the Sigma 17-70(c) dynamically assigns the pin-outs when it detects a camera is present.

Last edited by stevebrot; 02-02-2015 at 02:28 PM.
02-04-2015, 04:09 AM   #11
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Hi Pentaxians,

Thanks again for the comments.

Steve, the Sigma 70-300mm (just like the other AF lenses I tested the teleconverters with) works perfectly when mounted directly on the body, so this cannot be the reason for the problem. Also, you mentioned possible positioning/mounting problems or bad wiring. Well, the contacts seem to be at the right place and they look intact. The contacts are actually 2 pins connected with a copper spring so there are no solder joints, and the springs are not broken, either. (Once I find my multimeter I will check them for continuity but I guess if they were broken that would be visible and they would not keep the pins together, either.) Additionally, these teleconverters work properly with all KA lenses I tested them which also suggests that the 6 contacts are okay. Plus I have two teleconverters displaying the same problem and also found several reports about this issue (odd aperture displays when using KA mount teleconverters with autofocus lenses), so this suggests that this is not a specific case but something systematic. See for example:

https://www.pentaxforums.com/forums/58-troubleshooting-beginner-help/255683-v...#ixzz3Qg3eX8sC
Strange aperture reading with 2x Teleconverter: Pentax SLR Talk Forum: Digital Photography Review

Then I read Bojidar Dimitrov’s excellent article about the KAF mount and everything became clear:

The KAF mount features the same six electric contacts as the KA, and thus remains fully compatible with the older mounts. However, in addition to those (electric) contacts, it features a seventh - electronic one. Using a yet-unknown serial protocol, the body uses this contact to communicate with a digital chip contained inside the lens housing. The chip provides at least the following information:
- Focal length of the lens.
- Lens-to-subject distance.
- Exact selected aperture.
- Lens dimensions.

Features and Operation of the Kaf Mount

So it appears that the 6 contacts are needed to control the aperture from the body but the 7th contact is necessary to display it correctly.

And there came the idea: if my teleconverter has an extra contact (the Ricoh pin) that is exactly the same as the other 6 (2 pins connected with a copper spring) why not turn it into the 7th (electronic) contact? And I did! I documented the modding process and will post an article later.

And guess what: now the teleconverter works perfectly, it makes the body display the actual selected aperture with most autofocus lenses (Pentax FA series, Pentax DA series, Sigma DG series and Sigma DC series). (When I say correct aperture value I mean the native lens aperture without considering the two stops loss for the teleconverter).

Actually, there are 2 lenses that still make the body display incorrect apertures with the modified teleconverter: the Sigma 17-70mm F2.8-4 DC Macro OS HSM and the Pentax DA 18-135mm F3.5-5.6 ED AL [IF] DC WR. With these lenses, the displayed aperture values flicker between 4 and 5.6 (wide open) and 22 and 32 (at minimum aperture).

Both lenses have an internal focus motor while the lenses displaying correct aperture values all have screw drive focus. Interestingly, I experience the same problem with my Vivitar 2XMC7 AF teleconverter which have 7 contacts but no SDM contacts, either. I still have no clue how the lack of the SDM contacts affect the aperture value display. This is getting weirder and weirder. Any ideas?

I would not worry about this as would not use a teleconverter with these lenses anyway but as mentioned earlier, I planned to convert the teleconverters to extension tubes by removing the glass, so it is a problem if they cannot be used with these 2 lenses. Any suggestions are welcome.


Thank you all.
02-04-2015, 09:59 AM   #12
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QuoteOriginally posted by tarnag Quote
And there came the idea: if my teleconverter has an extra contact (the Ricoh pin) that is exactly the same as the other 6 (2 pins connected with a copper spring) why not turn it into the 7th (electronic) contact? And I did! I documented the modding process and will post an article later.
Now you have really lost me. The Ricoh pin does not mate to either your lens or your camera.

Oh, well...if you are happy that is what counts. Enjoy your TCs.


Steve
02-04-2015, 10:39 AM   #13
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For the OP, a simple question. Do you have a manual focus KA compatible body, pentax program plus or similar. It may be that the sigma lenses are not fully compatible if the data pin is not connected to an AF body.

Just to confirm this point, I took my older screw drive sigma 70-200/2.8 and attached to to a Takumar-A 2x teleconverter. The Takumar-A converter only has 6 pins, and on my K5 I can with the aperture dial select any aperture between F1.2 and F22.

It appears that clearly the 7th pin is necessary for Sigma lenses to set aperture with KAF3 mounts. I did not try on my PZ1 or *istD so I cannot comment on functionality there, but I also know that the takumar-A teleconverter works just fine with KA lenses on my bodies, so this is a specific quirk of sigma lenses not the cameras or Teleconverters.

I have not tried any of my pentax AF lenses to see if this is a behavior of all AF lenses when using a KA vs KAF teleconverter

Edit note,
i can now confirm both my sigma lenses, the 1-20 and 70-200 behave the same with the takumar A teleconverter (6 pins)
i can also now confirm that FA and DA lenses behave showing native maximum aperture at minimum focal length as tested using my FA 28-105 F4-5.6 and DA 18-50 F4-5.6

Last edited by Lowell Goudge; 02-04-2015 at 11:24 AM.
02-05-2015, 11:08 AM   #14
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QuoteOriginally posted by Lowell Goudge Quote
It appears that clearly the 7th pin is necessary for Sigma lenses to set aperture with KAF3 mounts.
I think you are essentially correct, at least for the zooms. I suspect that Sigma dynamically manages the contact pattern if the data pin is detected.


Steve
02-05-2015, 01:02 PM   #15
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When I use my DA lenses on my K10D with my 6 pin Vivitar Macro Focusing 2x TC they get treated as if they were manual focus "A" lenses. I have to set a focal length for SR, the widest rated aperture will show as the widest no matter what focal length is in use, the EXIF data will not show lens model/name or set focal length information.

As I recall there was some discussion that some Sigma lenses behave differently on teleconverters even if the data pin is present (and functional).
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