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09-26-2011, 06:19 PM   #1
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Pentax -F 1.7x AF Adapter works with M lenses?

I picked up an SMC Pentax-F 1.7x AF adapter.

It AFs fine with A-lenses but refuses to AF with M lenses.
Is that normal?

The F-stop translation does not seem to work 100% either.
I measured the resistance between front mount and back mount and it is a bit high (~60 Ohm). Could that be the problem?

09-26-2011, 06:26 PM - 1 Like   #2
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The 1.7x AF-A should work fine with both "A" and "M" lenses (in terms of AF). Obviously you have to use the aperture ring with the "M" lenses, but the AF of the converter should work fine.

Regarding the front to back resistance, my multimeter is MIA at the moment otherwise I'd check for you as I just got a 1.7x AF-A a couple hours ago
09-26-2011, 06:27 PM - 1 Like   #3
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Yup it should still work, just make sure they're focused to infinity.

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09-26-2011, 06:55 PM - 1 Like   #4
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Cant check mine currently,60 ohms flange to flange does seem bit odd.
Never checked mine,but assume flange(s) are part of ground plane,
which should indicate little difference between the 2.

Have you been able to determine that apeture coupling with "M" len(s)
stacked on AF is good to go.If those linkages are 'sticky',could be trying
AF while not stopped down,in that case,might not be enough light/contrast to do so.

Keep in mind that "A" lens will only report its own apeture with AF adptr,
and then only with apeture ring at "A" setting.
Isnt additive until "F" series or latter lens is mounted on AF adptr and lens
info chip is utilized.


Last edited by BillM; 09-26-2011 at 07:39 PM.
09-26-2011, 07:21 PM - 1 Like   #5
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QuoteOriginally posted by dgaies Quote
The 1.7x AF-A should work fine with both "A" and "M" lenses (in terms of AF). Obviously you have to use the aperture ring with the "M" lenses, but the AF of the converter should work fine.

Regarding the front to back resistance, my multimeter is MIA at the moment otherwise I'd check for you as I just got a 1.7x AF-A a couple hours ago
It should. I never tried it with an "M" lens yet.
It will prompt you for the focal length for SR and "correct" the f-stop on "A" lenses when the apeture ring is set to A(Auto). Setting apeture manually with the ring would not correct the f-stop just as per an M lens.
It obviously also works for later lenses F or FA or DA etc etc)

It will (should) AF with an M or K lens

I haven't tried this but with an M42- PK adapter you need a piece of foil on the contacts for it to work. (search here or look it up to verify how to do it)

You can also disable the AF of the adapter by taping over the contacts to the camera so you can use it just a a passive 1.7x converter for "Catch-in-Focus" with any lens.

When I get home in about 7 hours can test on an M lens and a multimeter.


The archived manual ( 1987 poorly scanned copy) is on the pentax website.

http://www.pentaximaging.com/files/manual/SMC_PENTAX-F_AF_ADAPTER_1.7X.pdf

Last edited by steve1307; 09-26-2011 at 07:28 PM.
09-26-2011, 09:14 PM - 1 Like   #6
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QuoteOriginally posted by Class A Quote
I picked up an SMC Pentax-F 1.7x AF adapter.

It AFs fine with A-lenses but refuses to AF with M lenses.
Is that normal?

The F-stop translation does not seem to work 100% either.
I measured the resistance between front mount and back mount and it is a bit high (~60 Ohm). Could that be the problem?
The F stop with M lenses is invisible to the DSLR's because the KAF-3 mount dropped the mechanical follower. The AFA 1.7x works just fine with both my M 100/4 macro and my M 400/5.6. With the 400 particularly, I have to get focus close to correct first and it will then fine tune things for me. It is focal length dependent. The longer the lens, the closer you have to get before it will work properly. Also with the 5.6 aperture, I need pretty good light on the subject with a good contrast edge.
09-26-2011, 10:38 PM - 1 Like   #7
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This is how my Pentax 1.7X AFA behaves with my K-7 and K10D:

- It blocks the focal length data from the lens to the body. When you attach the lens, the body asks for the focal length. This applies to ALL lenses.
- It treats ALL lenses as manual focus. The auto focus is done by that AFA. Due to the limit of the AFA's auto focus range, the lens has to be roughly in focus for auto focus to work.
- Metering mode is the same as the lens by itself: if the lens is on manual metering (the lens has an aperture ring which is not at "A"), the combo behaves like a manual lens (M only, use green button). If the lens is on auto metering (no aperture ring, or aperture ring at "A"), the combo behaves like an auto lens.
- In auto metering, the AFA modifies the aperture data to the correct value (e.g. shows the largest aperture as F/4.5 if that of the lens is F/2.8).
- In manual metering, the aperture data doesn't show (just like the case of a manual lens).

If I use a piece of Scotch tape to cover the contacts of the AFA (between the AFA and the lens), the combo doesn't focus at all. This can be the symptom that the OP observed. The lens may have a painted (or anodized) mount. If this is a case, a strip of aluminum foil can fix the problem.

Last edited by SOldBear; 09-26-2011 at 10:43 PM.
09-26-2011, 11:45 PM - 1 Like   #8
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QuoteOriginally posted by SOldBear Quote
In auto metering, the AFA modifies the aperture data to the correct value (e.g. shows the largest aperture as F/4.5 if that of the lens is F/2.8)
Just looked at both of mine,Bear is right about additive apeture.
Didnt bother to check in manual and assume thats why I havent noticed before,
almost always shoot manual.
Went flange to flange on both adaptrs and shown 3.5 ohms app.
60 ohms could indicate fouled/dirty mount.
Didnt go point to point with contacts,just flanges. might be worth a shot to
follow through with what Bear mentions at end of post to trouble shoot further.

09-27-2011, 03:08 PM   #9
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Many thanks to each and everyone who responded to my question.

Much appreciated!

Individual responses below:

QuoteOriginally posted by Adam Quote
Yup it should still work, just make sure they're focused to infinity.
Yeah, getting the lens focus in the right ball park isn't the issue. The camera just doesn't attempt to focus at all if I mount a non-A lens on the adapter.

I reckon it has to do with overall conductivity problems.
The chip inside the adapter could be toast, but I don't think so as these things are rather robust.

QuoteOriginally posted by BillM Quote
Cant check mine currently,60 ohms flange to flange does seem bit odd.
There is a spring-loaded rod connecting the two flanges and at the spring side the backside of the flange seems to be a bit dirty. I'll try to clean it well and that should help with lowering the resistance.

QuoteOriginally posted by BillM Quote
Have you been able to determine that apeture coupling with "M" len(s)
stacked on AF is good to go.If those linkages are 'sticky',could be trying AF while not stopped down,in that case,might not be enough light/contrast to do so.
The mechanical aperture coupling works fine. Lenses stop down as they should (with optical preview and during shots).

QuoteOriginally posted by steve1307 Quote
I haven't tried this but with an M42- PK adapter you need a piece of foil on the contacts for it to work.
Is that because the M42-PK adapter does not short any of the contacts?

QuoteOriginally posted by steve1307 Quote
You can also disable the AF of the adapter by taping over the contacts to the camera so you can use it just a a passive 1.7x converter for "Catch-in-Focus" with any lens.
Thanks for the hint. At the moment I'd love to get the AF going for non-A lenses. I think I'll get it to work one way or the other even if it means to permanently short one of the adapter contacts.

QuoteOriginally posted by steve1307 Quote
When I get home in about 7 hours can test on an M lens and a multimeter.
I'd be interested in your reading.

QuoteOriginally posted by steve1307 Quote
The archived manual ( 1987 poorly scanned copy) is on the pentax website.
Wow, thanks heaps!

QuoteOriginally posted by Canada_Rockies Quote
The F stop with M lenses is invisible to the DSLR's because the KAF-3 mount dropped the mechanical follower.
Sure, my problem is that the AF doesn't work with M lenses. I'm optimistic, though, that I'll get it to work.


QuoteOriginally posted by SOldBear Quote
This is how my Pentax 1.7X AFA behaves with my K-7 and K10D:
Thanks for the list! It is consistent with what I observed (and what the manual says).

QuoteOriginally posted by SOldBear Quote
If I use a piece of Scotch tape to cover the contacts of the AFA (between the AFA and the lens), the combo doesn't focus at all. This can be the symptom that the OP observed. The lens may have a painted (or anodized) mount.
I tried several manual lenses and none of them worked. Would be odd if the mount of all of them would not be conductive. But I'll try to use a piece of foil just to make sure.

Last edited by Class A; 09-27-2011 at 03:14 PM.
09-27-2011, 03:16 PM   #10
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QuoteOriginally posted by BillM Quote
Went flange to flange on both adaptrs and shown 3.5 ohms app.
Thanks heaps! I'll try to get at least close to that value.
09-27-2011, 03:56 PM   #11
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BTW, my initial test shots are very encouraging. Optically the 1.7x AF seems to be considerably better than any other TC I've tried before.

In September 2010 the 1.7x AF was still available brand new from Japan. I guess that source has dried up, has it?

EDIT: Seems the adapter is still available in mint condition. But US $548 is too rich for my blood. I hope I can coax my copy into working condition again.

Last edited by Class A; 09-27-2011 at 05:49 PM.
09-27-2011, 04:17 PM   #12
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QuoteOriginally posted by Class A Quote
I tried several manual lenses and none of them worked. Would be odd if the mount of all of them would not be conductive. But I'll try to use a piece of foil just to make sure.
That is weird.

Try the piece of Al foil between the AFA and the lens, and also between the AFA and the camera body (not both). The result may be interesting.
09-27-2011, 07:14 PM   #13
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Assuming its OK with many other lenses then the Body - to AFA would be fine.

The adapter won't AF if it thinks there is no lens attached. It is connecting across the relavent pins in th AFA which is important.

Here's a video from YT (not mine). He just bridges the contact pins to make it function.

for interest:
The AFA 1.7x has 6 pins on the lens side which is why it all later lenses behave like an "KA" mount
Features and Operation of the Ka Mount

Later KAF mount has 7pins so the lens focal length is read (among other information).
With the AFA you have to input it on all lenses and don't get matrix metering (i guess)
09-27-2011, 08:47 PM   #14
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Today I tried to AF my SMC Takumar 55/1.8, found on a discarded Spotmatic F. It supports the premise that lack of shorted pins will prevent AF. On my K10, it also refused to Catch-in-Focus, and the only thing I can think of is the painted mount on the old lens. I will try to short things out and see what happens. Interesting thread.
09-28-2011, 04:03 AM   #15
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We have not really heard it all from classa as to getting the AFA working but here is how it works on non A lenses such as K and M lenses

First you need to enable use aperture ring because the camera won't work at all without this

The aperture will show F--- that's normal

Aperture is set on the lens and exposure is manual mode via green button

Focus is manual until you get close to correct focus, then the AFA will achieve final AF lock

If the lens attached is not conducting mount it should still function because the only important pin is the AF data pin

With an A lens the camera will readnthe true combined aperture, as the AFA has circuitry that corrects for the addition qof the adaptor and adds 1.5 stops to the aperture. Therefore resistance readings are not the way to determine this adaptor is OK or not
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