[gjw297]

I appear to have developed a mild form of LBA and in the process have acquired a number of Tamron adaptall (1 and 2) primes, which I get on well with. I've got one PKA mount and several PK mounts for them. Obviously the PKA mount makes the lenses easier to use on my DSLR body and I'd like more of them, but then I have seen what they sell for on ebay!

Looking at the PK/PKA mount adaptors, they appear mechanically fairly similar, but with electrical contacts.

I was toying with the idea of trying to convert a spare PK mount adapter into a PKA one. Before I start dismantling my PKA adaptor, I'd be grateful for any thoughts/pointers on such a conversion? I wondered if anyone on here could enlighten me about how the electronic side of the PKA mount works and if such a conversion might be possible (given access to machine tools and electronic engineering expertise?)

Thanks in advance.

[OrenMc]

Its probably possible but not that simple I would say, unless you already have all the tools and time. Might be a fun project.

[alfa75ts]

Interesting idea, I currently only own a PK/A adapter but here's my 2 cents:

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.

[gjw297]

Thanks Alfa75ts, that sounds feasible and has got to be worth a try. I feel slightly embarrassed that I didn't do a bit more research before asking!

It sounds like it would be sensible to approach this in two steps: first make a mount with contacts matched to hard wired AE operation for the aperture range of one of my lenses (e.g. 2.5-22). If this works, I've got enough mounts that I could do it for all the lenses that I need.

However, reproducing the contact PCB as well, to allow automated aperture range detection sounds like a challenge and would ultimately be a proper job. I've got a friend who has access to PCB manufacturing facilities... I think that making a contact connecting the (*) contact to the mount body when the AE aperture position is selected is not insurmountable on the PK mount either. I'll take one apart later and have a look.

[MattGunn]

I have tried modifying a k adapter to a KA adapter and it workes ok with some lenses. As is sugested above I drilled holes in the back of the mount where there should be insulators and filled them with Araldite (although I have subsequently found that Miliput workes better). I also drilled a hole where the A pin should be and fitted an A pin and very small spring scavenged from a badly broken lens. I made the mout to suit the lens I had and so put the insulator in to get an a range from f/2.8-22. I also drilled a hole for a screw to lock the aperture ring on the AE or fully closed position. The holes were located acurately using a jig.
I first tested the mount with an adaptal searies 1 35-80mm f/2.8-3.5 (model QZ 35M) and then a searies 1 70-150 f/3.5 (model QZ 150M) With both of these lenses the exposure was fine wide open but got steadily worse as the aperture was closed down and then improved again towards minimum aperture. At its worst the exposure was out by nearly 2 stops. I then got hold of an adaptall 2 28mm f/2.5 (model 02B) and on this the mount workes fine at all apertures.
I am not sure why it workes with the newer lens but not the older ones but I suspect that the older lenses may not have been designed to work with the KA type adapters and so the aperture area does not vary linearly with the lever displacement. I have not been able to confirm whether it is the lenses or the adapter though as I don't have a proper KA adapter (as these cost more than I paid for all 3 adaptall lenses).
From my experience I think it is worth pursuing the modification of K adaptall mounts but I don't think that there is room for a PCB without totally rebuilding them. I will post some pictures of my modified mount later when I get home. In case you have.t found it yet there is a lot of usefull info on adaptall lenses here: Adaptall-2.com

[alfa75ts]

G'Day Matt,

A relevant quote from the Pentax K mount wiki:

"The aperture on the lens is set from the body by the same stop-down lever found on the original K mount, but on KA lenses this lever is proportional to the area of the aperture opening, rather than the diameter as on previous lenses. This allows the body to easily set a specific aperture, since the relationship to F stops is linear. The lenses add an 'A' setting on the aperture dial, which gives the body control of the aperture."

It sounds like Adaptall lenses are like 'M' lenses and Adaptall-2 lenses are like 'A' lenses.

[pacerr]

The holes were located acurately using a jig.

Take the body mount-plate from a trashed type-A body and use it for a template and jig when spot drilling the new lens mount. Index it off the latch pin and mating notch on the lens for convenience.

If you don't have a donor-body, print a 1:1 template on heavy photo paper - that's a good exercise in precision macro work too. Or I suspect you can even scan a mount and tweak it as necessary.

This jig facilitates mount conversions of any kind. It's REALLY easy to start spot drill for pins and insulators on the WRONG side of the index mark if you're not paying attention. (Yes, I've got the T-shirt - but it's pretty much a harmless mistake. Just fill the "bad" hole with epoxy and shave it smooth so you don't make a custom "Ricoh-pin hole".)

H2

[alfa75ts]

Well I just received a KM adapter and I don't think it's modifiable (at least not to a full function PK/A adapter).

1/ The 'P' lever (in previous pic) is missing so I think you would be limited to Matt's 'locked in AE (P) mode' method.

2/ The movement/design of the stop-down lever is different and I doubt that it can be used by the camera to set an accurate aperture. But Matt's test on an Adaptall-2 lens seems to prove me wrong.

There is however room for the circuit board but given the other issues it's probably better to just hard-code the aperture range.

[MattGunn]

Here is a picture of the modified mount. The insulators and the A pin can be seen on the right and the aperture ring locking screw on the left. Other than these the mount is unchanged. I will have to get my hands on some other adaptall 2 lenses to try the mount with sometime to see if the modified mount workes with other lenses. I will also have to get hold of a proper KA mount sometime for comparison.
Looking again, there probably is room for a small pcb but it would involve a lot of work and modification to fit one with the switches / contacts you'd need to select the aperture range.

[Lowell Goudge]

For the A pin, I modified a K mount lens to KA using a spring loaded contact designed for PCBs to mount grid array ICs

scavaging spring loaded pins from dead lenses also works

making a generic KA from K mount is not possible because the KA adaptor has a small sliding contact arrangement connedted to the two pick up points for the adaptor to the lens, this is how they changed the contact arrangement with the individual lenses to report maximum aperture.

you may also want to check the motion of the aperture blades between K and KA adaptor to make sure the mechanism controls them the same way.

At best the arrangement would be specific for each maximum aperture only

[chse]

I first tested the mount with an adaptal searies 1 35-80mm f/2.8-3.5 (model QZ 35M) and then a searies 1 70-150 f/3.5 (model QZ 150M) With both of these lenses the exposure was fine wide open but got steadily worse as the aperture was closed down and then improved again towards minimum aperture. At its worst the exposure was out by nearly 2 stops. I then got hold of an adaptall 2 28mm f/2.5 (model 02B) and on this the mount workes fine at all apertures. Adaptall-2.com

I am surprised that it works with any lens. The PK adapter is levered, meaning that the aperture lever is fixed at a single point with a screw. This causes the effective lever to be long at full open and full closed position but to be shorter at the middle position. Thats why its movement is not linear.
The PKA has no lever in the common sense but the the aperture 'bar' is on a slider which moves parallel to the mechanism which opens and closes it in the camera, thus it is linear.

[MattGunn]

It sounds like Adaptall lenses are like 'M' lenses and Adaptall-2 lenses are like 'A' lenses.

I have found much the same information elsewhere and had also concluded that the Adaptalls had an M like mechanism and the Adapatall 2's an A
like mechanism. If anyone has used a proper KA mount with the older adaptall lenses then this can be confirmed (if it doesn't expose properly) or proven wrong (if it exposes corectly).

Take the body mount-plate from a trashed type-A body and use it for a template and jig when spot drilling the new lens mount.

I didn't have an A mount from a camera so I used an old KA mount of a lens to spot drill a jig and then used the jig for spot drilling other lens mounts. The Mount I started from has since been modified and fitted to the back of a Zeiss Contax Yashica fit lens.

I am surprised that it works with any lens. The PK adapter is levered, meaning that the aperture lever is fixed at a single point with a screw. This causes the effective lever to be long at full open and full closed position but to be shorter at the middle position. Thats why its movement is not linear.
The PKA has no lever in the common sense but the the aperture 'bar' is on a slider which moves parallel to the mechanism which opens and closes it in the camera, thus it is linear.

I suspected that there were differences in the mechanism between the KA an K mounts but have not had the opertunity to examine a KA mount closely. If anyone would like to post a close up shot of the mechanism of the KA mount then I would be greatfull. I have done some further testing with the 28mm f/2.8 and the exposure is not perfect over the whole range and there is a bit of under exposure around f/16-22. This may prove the difference between the Adaptall and Adaptall 2 lenses theory wrong and I may have just been lucky that it is so close to working right with this one lens. With more information and a bit of time I may have a go at the mechanism in the K mount to see if it can be adapted to give a more linear aperture movement.

[chse]

The Mount I started from has since been modified and fitted to the back of a Zeiss Contax Yashica fit lens.

You modified a tamron K mount to fit Yashica? You know there are y/c mounts for Tamron? To bad- I actually could have traded one for a K-mount.

I have done some further testing with the 28mm f/2.8 and the exposure is not perfect over the whole range and there is a bit of under exposure around f/16-22. This may prove the difference between the Adaptall and Adaptall 2 lenses theory wrong and I may have just been lucky that it is so close to working right with this one lens.

I have tested both a Ricoh mount and a PK mount with a 90mm/2.5 a 80-200mm/2.8 and a 24/2.5. I set different smallest apertures using scotch tapes since I thought maybe the ranges have to be adjusted, but none of them came even close to the right exposure. Its interesting that it works with a 28mm, what minimal and maximal aperture did you set? I have a 28mm, too but never tested it.
Even a PKA mount is far from being perfect, I have three and 2 of them loose about 1/2 a stop when closed down. They can be adjusted but its hard to get it perfect. Not opening the aperture before removing them easily get them out of adjustment.

I post some pictures of the mounts.

[chse]

Here the PKA mount in open and closed position




The PK mount


And the Ricoh RI mount

[MattGunn]

You modified a tamron K mount to fit Yashica? You know there are y/c mounts for Tamron? To bad- I actually could have traded one for a K-mount.

No, I scavenged a KA bayonet from a totally trashed Tokina zoom lens. I used it to spot drill the jig which I then used to spot drill the holes in the tamron mount. I have subsequently modified the bayonet and fitted it to a Carl Zeiss 60mm f/2.8 S Plannar T macro which was originally contax mount.

Its interesting that it works with a 28mm, what minimal and maximal aperture did you set?

The insulators were put in for f/2.8 to 22. I have used it over the whole range.

Even a PKA mount is far from being perfect, I have three and 2 of them loose about 1/2 a stop when closed down. They can be adjusted but its hard to get it perfect. Not opening the aperture before removing them easily get them out of adjustment.

The 28 with my modified mount is about 0.5-1 stop down at f/22. It sounds like although its not perfect, on this lens it no worse (and a lot cheeper) than a proper PKA mount.