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09-04-2009, 02:05 PM   #1
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Confused: Adaptall Pk/A Adapter Max. Aperture Issue

I've read a couple of threads on this matter, and tried a couple of times to do the thing described - but I just can't seem to make it right! Right now, I have polished the right-top screw described here. I tried using the multimeter to check resistance between that screw and the mount base, and it's always 0 (I have 2 AD2 lenses, one with max f/4 aperture, another with f/3.5; f/4 works, I'm trying to make f/3.5 work).
Now, I'm getting confused. Was I doing the right thing, or was I supposed to polish the area *around* that screw?
If anyone had the same problem as me, and managed to make it work, can you take a picture of the mount? Or try and explain what I did wrong...

Thanks!

09-04-2009, 04:00 PM   #2
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The Tamron Adaptall 2 - PK/A concept is a 20+ year old design adapted to work with all major cameras. Note that the Adaptall 2 lens adapter only uses three pins to convey the information of 5-7 Pentax pins. The lenses themselves don't exceed f2.5 - so there are some recognized compromises in the data reflected in many cameras. Auto focus was not an economically competitive option.

Don't try to get too technical here. Make some trial shots at extreme f-stops and see what results you get. At worst, you may have to remember to apply a little correction to suit your preferences. At best, you'll discover it just works - it just doesn't display normally. Experiment. Have a little fun.

The Adaptall 2 and SP glass was, and still is, pretty impressive and for the present cost of those lenses they're a bargain if you can adapt to MF and use good judgement in exposure. (The instant histogram is the most under-utilized advantage of the DSLR - IMO.)

It amamazes me to see some of that glass designed at the end of an era and built to very high, competitive standards selling for $20-50 today.

H2

Last edited by pacerr; 09-04-2009 at 08:06 PM.
09-04-2009, 04:31 PM   #3
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The illustration is a little misleading. Those are not screws. They are index marks related to manufacturing. The contacts are the metal parts surrounded by black plastic. Make sure that the metal of those contacts is free of any coating or foreign substance. Ditto for the surrounding plastic insulation. A gentle scrape with the blade of a screwdriver should be enough.

As for the number of contacts, compromises, etc...The three (actually four including the "A") contacts on the lens are enough to convey the required information. The coding of the contacts is boolean (on/off) and the patterns are on the Web at:

Pentax Lens Modifications for Matrix Metering - Mark Roberts Photography

If I remember correctly, Tamron uses contacts 1, 2, A and 5 to cover the range from f/2.5-f/4 max with f/22 min. (Contacts 3 and 4 are missing and therefore always "high".)

Steve

BTW...I have a the Tamron 70-150/3.5 and it identifies as f/4 max. Sorry to say, but Tamron is known to have fudged the maximum aperture of some of their lenses. Mine is one of them.

BTBTW...Ignore the rest of Robert's excellent article...it does not apply to your camera...

Last edited by stevebrot; 09-04-2009 at 04:54 PM.
09-04-2009, 06:44 PM   #4
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QuoteOriginally posted by stevebrot Quote
If I remember correctly, Tamron uses contacts 1, 2, A and 5 to cover the range from f/2.5-f/4 max with f/22 min. (Contacts 3 and 4 are missing and therefore always "high".)
Your memory is pretty good, the only thing is the 'A' contact has nothing to do with the range.

Below is a copy of my post from the Tamron adaptall mount PK to PKA conversion?
thread.

------------------------------------------------------

Referring to the pic below and these two sites 1 2

The PK/A adapter only has three switchable pins where Pentax uses six(+) and pin * is used to indicate 'P' (AE) mode leaving only two switchable pins to change the indicated aperture range of the lens.

1 on the pic below is an insulated spot on the flange which permanently indicates a '0', the locations where 3 and 4 would be permanently indicate '1's.

So the only aperture ranges available are:

123 45
001 10 4.0-22
001 11 3.5-22
011 10 2.8-22
011 11 2.5-22

These are selected by the position of lever "A" in the pic below moving contacts on the small circuit board in the adapter. This would be quite difficult to make so I would suggest making four adapters (one for each range) by drilling dimples at the positions where you want a '0' and filling the dimples with epoxy (as per 1 on the pic below). (You could also make other adapters with different aperture ranges that the adaptall adapters can't do)

Next the '*' position, this is electrically connected to the mount body when the lens aperture setting is in the AE (P) position and is switched by the movement of the 'P' lever in the pic below. I don't have an answer for this yet, I don't have a 'K' adapter to examine.

Hope this helped.



------------------------------------------------------

I have since realised that pins 12&5 give a binary value which when added to 10 gives the number of half stops that the maximum aperture is from the minimum aperture given by pins 3&4.

But all this may have very little to do with the original post.

09-04-2009, 08:30 PM   #5
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QuoteOriginally posted by alfa75ts Quote
Your memory is pretty good, the only thing is the 'A' contact has nothing to do with the range....
I had not put the "A" contact in the list, some guy would have posted that it is essential to determine whether to evaluate the other 2 switchable positions...

Steve
09-04-2009, 09:49 PM   #6
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Okay.... So, I have the SP70-210/3.5, and I also have an 80-210/3.8~4. On both lenses, adapter fits without moving the pin; multimeter also shows that 5th pin (which makes all difference between 3.5 and 4 max. aperture) has infinite resistance with the lens mount - when mounted to any of the two. So, camera recognizes both lenses as f/4 max aperture.
That sucks! This means that, whenever I use the 70-210/3.5, I will have to subtract half-stop from what's indicated - so, when it says, f/4, it's actually f/3.5; when it says f/4.5, it's actually f/4, and so on. Aww....
09-04-2009, 10:31 PM   #7
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Just 1 point, you must have the aperture set to AE to get valid readings from the pins.
09-04-2009, 10:37 PM   #8
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QuoteQuote:
Just 1 point, you must have the aperture set to AE to get valid readings from the pins.
Yeah, I know...
Actually, I might look into converting PK->PK/A later, when I get the necessary materials and a PK adapter.
I just fiddled a bit more with Pk/A adapter I had, and I managed to make the lens recognize as f/3.5 - before mounting Pk/A adapter, I twitched the A-lever just a bit, and forced the adapter onto the lens (so now, one lever is in place as it should be, and another is just a bit off). The lens recognizes as a f/3.5 lens and stops down as it should. Since what I have done stays on, but looks a bit finicky, I might look into enhancing it later on.

09-06-2009, 08:12 PM   #9
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QuoteOriginally posted by pbo Quote
Yeah, I know...
Actually, I might look into converting PK->PK/A later, when I get the necessary materials and a PK adapter.
There are several threads about this here - don't bother it does not work (except for maybe with the 28mm/2.5)

QuoteOriginally posted by pbo Quote
I just fiddled a bit more with Pk/A adapter I had.
You might want to try to take the black plate off the adapter which faces the lens. Underneath you can see the contact springs which connect to the mount and set the function of the pins with the lever you describe. Sometimes the springs are bend or the contacts dirty. The springs are very fragile, you will need some fine forceps or try to manipulate them with needles or fine watchmaker screwdrivers.
09-15-2009, 01:53 PM   #10
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I want to tag this thread as I often have issues with lose contact in my tamron pk-a adaptall-2 adapter which shows F-- in Av mode not displaying the apertures correctly.

I did scrape off the connector and it looks like the adapter is not contacting the contacts correctly. I have two copies of Tamron pk-a adaptall-2 adapters with one sold. Both have intermittent problems. Sometime a wiggle will set it back to normal but it is not working all the time. I need to revisit to have a final fix for this problem

Thanks,
Hin
09-15-2009, 02:27 PM   #11
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I don't know if it is the problem you have, but one of mine was flakey and I had to add some bend to the little copper wipers in the mount. They slide over a little piece of pcb and mine would lose contact sometimes. It has been a while ago but I don't think it was hard to do.
09-15-2009, 06:46 PM   #12
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QuoteOriginally posted by stevebrot Quote
The illustration is a little misleading. Those are not screws.
I thought they were tips of screws, i.e., the other end that is not the head.
While it is important that the contacts are conductive , it is also important that the screw tip / index mark next to the contacts is conductive. Otherwise, the adapter won't work.

QuoteOriginally posted by stevebrot Quote
BTW...I have a the Tamron 70-150/3.5 and it identifies as f/4 max. Sorry to say, but Tamron is known to have fudged the maximum aperture of some of their lenses.
Does your adapter work for other f/3.5 lenses? My 70-210/3.5 is correctly identified with f/3.5. Sometimes it requires a little wiggling on the lens mount and/or aperture ring to make the f/3.5 happen.
09-15-2009, 07:30 PM   #13
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QuoteQuote:
Does your adapter work for other f/3.5 lenses? My 70-210/3.5 is correctly identified with f/3.5. Sometimes it requires a little wiggling on the lens mount and/or aperture ring to make the f/3.5 happen.
Mine does show 3.5 if I force the adapter to lock onto lens with A-lever (shown in a pic in one of the above posts) a bit off-place (i.e. it doesn't go into its slot, but a bit to the side of it)
09-15-2009, 08:43 PM   #14
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This may, or may not, be a solution for any specific adapter but since dirty contacts are one potential problem a spritz on the inside with electronic contact cleaner may help.

H2
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