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02-25-2012, 09:53 AM   #1
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DA lens compatibility with various TCs

Executive summary: the vaunted Pentax compatibility doesn't necessarily apply to TCs. Putting an A-type lens on certain AF TCs, or putting a DA-type lens on an A-type TC, may result in incorrect aperture data reaching the camera. Also, DA* lenses have their own quirks with certain TCs. In brief, don't assume general compatibility between A- or newer lenses and TCs.


I now own two types of teleconverter (TC) and have found an interesting range of compatibility issues with various DA-type lenses. Sharing this here because I haven't yet found this information put together, and in hopes of gleaning more info (or a better explanation) from my fellow forum members.

A while back I bought the Pro-Optic 1.4x TC. You can read my review at that link, and more discussion about the issues I and others have found when pairing this TC with a DA* lens. (The same TC is available under many different brands.) Short answer: this TC seems to be fully compatible with normal DA-type lenses, but has odd quirks when you put a DA* lens on it. If you short the data pin on the lens side of the TC, you solve the quirks but then get incorrect aperture data. The TC does work fine with ordinary DA lenses.

More recently I've bought a couple of KR-type TCs, i.e. plain KA mount after I removed the Ricoh pins. (Details in my review at the link.) Hey presto, they work correctly with the DA* 200! No AF, of course, but aperture data is correct and there is none of the quirky behavior seen with the Pro-Optic TC. Of course A-series lenses are fully compatible. Now it's the DA lenses that aren't. With at least some DA-type lenses mounted on this TC, the camera will not show the correct aperture range. (At least one lens does show the correct aperture data, but that might be dumb luck.)

Update, 2012/08/15: I've since acquired a Sakar TC with PZ contacts on both sides, and my first FA lens (50/1.4). My DA* 200 works correctly on that tube in all respects except for AF, which still doesn't work, despite what appear to be working PZ contacts. Unlike the Pro-Optic TC, the Sakar has all 7 pins on both sides (no bare metal). My other (not *) DA lenses and my FA 50 work correctly on it. Inexplicably (to me), despite the conductive #5 pin on this TC (see below), my A400/5.6 does not report the correct aperture range with it.

My experience with the Pro-Optic/DA* combo got me delving into the details of how the data contacts work in KA and later mounts. Far and away the best source I've found is on Bojidar Dimitrov's site: K-Mount Evolution, Features and Operation. I'm still far from a complete understanding, but I'm developing some guesses.



Background info: If you look at the mount on a Pentax DSLR, you'll see a group of 7 electrical contacts at bottom left (as you face the front of the camera). One of these is slightly recessed compared to the others. In keeping with the link in the above paragraph, I'll refer to these contacts right to left, i.e. starting at the bottom of the mount. The first is the data contact, found on F-series and newer lenses. This transmits data in a serial protocol, including focal length. The remaining 6 contacts are the standard A-series contacts. Unlike the data contact, these are simple on/off contacts. Again going from right to left, I'll refer to these as pins 1 through 6. Pins 1, 2, and 6 encode the magnitude of the aperture range, in stops. Pins 3 and 5 encode the minimum aperture. Pin 4 (the recessed one) tells the camera whether or not the lens is in the A setting.

If you have any A-series lenses, look at the mount and you'll see one or more non-conductive plastic dots. (Exception: the A50/1.2 won't have any.) You'll also see a gold nub corresponding to pin 4, above. Note that if you move the aperture ring in and out of the A setting, the gold nub will move a little. It is the pattern of non-conductive nubs that tell the camera the aperture range of the lens.

Starting with the F-series, this pattern of conductive vs. non-conductive contacts has been largely hidden from view. From what I've seen, all lenses from F-series on have a similar pattern of data pin, metal nubs for pins 1, 2, 4, and 6, and bare metal in place of pin 5. Pin 3 varies: it is a metal nub in DA*-type lenses (including Sigma HSM lenses), bare metal in plain DA-type lenses, and either bare metal or a non-conducting nub in FA- and F-type lenses.



On to some scattered observations, tentative conclusions, and outright guesses:

The DA* 200 has an aperture range of f/2.8 to f/22. As per Dimitrov, this corresponds to a pattern of 011*10 on the six A contacts, i.e. pins 1 and 6 should be non-conductive. Since this lens, like all F-series and later lenses, has metal nubs at positions 1 and 6, and since the camera gets the correct aperture range when the lens is paired with an A-series TC (no data pin), the lens must have some internal mechanism for making those nubs non-conductive.

Putting this lens on the DA-type TC (Pro-Optic), aperture data is still correct but the camera goes somewhat bonkers, various buttons no longer working. Speculation: the lens says, hello, I am a DA* lens. The camera says, I'm not getting an SDM connection -- this does not compute -- danger, danger -- I'm sorry Dave, but I can't do that.

Shorting the data contact on the TC (lens side) gets the camera fully working again, but now the aperture range is incorrect, showing as f/5.6 to f/32. Again, per Dimitrov, this corresponds to 000*10. That is, all pins non-conductive except for #4 (the A-setting pin) and #5 (which is bare metal on the lens). Why is the aperture range correct on the plain A-type TC, but incorrect on a DA-type TC with the data contact shorted? Speculation: I shorted the pin by with a piece of foil covered by insulating tape. For the lens's aperture pins to conduct, the lens requires a connection to the camera through the data pin, even if it is just to the bare metal of the mount. I haven't tried shorting the pin so that the lens still gets this connection, but I don't want foil getting lose in the camera and I'm not quite curious enough to try it yet.

Clearly the plain DA lenses work differently. With both DA lenses I've tested, on the A-type TC I get f/4 to f/22 at all zoom settings. This corresponds to 001*10, i.e. all aperture pins non-conductive except for #4 and the two contacts (#3 and #5) that are bare metal on every DA lens. This happens to be the correct range for the DA 16-45, but I guess that is just a coincidence. My guess is that plain DA-type lenses require an active data connection with the camera to work correctly, unlike the DA* line. I can't explain why, but that's the only hypothesis I can fit to the data.

With the Sigma 70 macro, also a plain DA-type lens, with an actual aperture range of f/2.8 to f/22, on the A-type TC I see f/1.2 to f/22. This corresponds to 111*11, all pins conductive. So the Sigma version of DA seems to have the same requirement for an active data connection, but defaults to conductive instead of non-conductive contacts. Same difference.

One more little quirk: the Pro-Optic TC and its brethren have bare metal on the camera side at the pin #5 position. The #5 contact needs to be non-conductive for lenses with a minimum aperture of f/16 (no Pentax lenses, but some third-party lenses) or f/45 (e.g. Pentax super-telephotos with 5.6 or smaller maximum aperture). I can confirm that this TC is not compatible with the Pentax-A 1:5.6 400mm, unless you insulate the bare metal at contact #5.

Query: I looked over the reviews of the various Pentax TCs, most of which are plain A-type, but there was very little about compatibility with F, FA, or DA lenses (other than the * lenses, which seem to work differently). Anyone have experience here?

Practically speaking

In general, TCs need to be matched with lenses from the same mount series for full compatibility. Some other combinations are usable (e.g. DA* lens on A-type TC, most A-series lenses on DA-type TC), others are quirky at best.


Last edited by baro-nite; 08-15-2012 at 04:42 AM. Reason: clarification; update
02-25-2012, 05:01 PM   #2
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QuoteOriginally posted by baro-nite Quote
Query: I looked over the reviews of the various Pentax TCs, most of which are plain A-type, but there was very little about compatibility with non-* F, FA, or DA lenses. Anyone have experience here?
They'll work fine, but manual lenses still be manual. For example, I've used the 1.4x-L with the K 500mm and gotten great results!

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02-25-2012, 05:32 PM   #3
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Not sure I put that question clearly -- I was wondering about compatibility with F-, FA-, and DFA- lenses, but not the * lenses. For example I note that the compatibility list for the 1.4x-L converter includes F*, FA*, and DA* lenses, but no non-* lenses. Maybe that only has to do with physical compatibility due to the extending element on the TC, but I was wondering if there is some difference in how * and non-* lenses transmit aperture data.
02-25-2012, 07:30 PM   #4
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There was an inconclusive discussion a while back on the topic of the lens contacts on DA/DA* lenses and some speculation that the five 'legacy' contacts are now used for more than just encoding min. aperture and aperture range. Pin positions on some newer lenses have changed from just being a short (the mount itself) or an insulation (or cut-out) to become an insulated pin which could indicate either tri- or four-state state logic per pin or perhaps a digital signal.

So the use of the electrical contacts may not be as simple anymore as on A, F and FA lenses, and third party teleconverters do perhaps not transfer the data correctly.

This complexity could also be the reason that Pentax has not released an auto focus teleconverter despite for years having announced that one would be coming.

02-25-2012, 07:53 PM   #5
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Thanks Ole -- your mention of the previous discussion got me to try searching again, and I came up with these threads:

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/124854-infos-p...ent-fa-da.html

https://www.pentaxforums.com/forums/pentax-beginners-corner-q/146586-kaf-pin-...ram-guide.html

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/117613-convert...ml#post1216725

Good discussion and I'll have to digest it for a bit. As you say it looks like we're still speculating. I'd still like to hear of anyone's experience using DA (not *) lenses with the Pentax A-type TCs.

Edit: Another good link with info on specific TC/lens combinations:

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/128273-da-zoom...ml#post1332279

Last edited by baro-nite; 02-26-2012 at 07:33 AM. Reason: additional info
02-26-2012, 07:39 AM   #6
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QuoteOriginally posted by Ole Quote
So the use of the electrical contacts may not be as simple anymore as on A, F and FA lenses, and third party teleconverters do perhaps not transfer the data correctly.
I'd think the TC only needs to provide simple conductive connections between all lens and camera contacts, and let those two work out the details. Maybe more to do with the question of translating effective focal length and aperture? But I speak from great ignorance concerning electronics.
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