[newarts]

It turns out that short circuiting the "A" pin (the slightly depressed electrical contact) when an m42 or M lens is mounted enables TTL flash if the DATA pin (nearest the bottom of the lens mount) is also shorted out (K100D).

A smooth metal surface like the base of an M lens does not make contact because the "A" pin is below the mount surface.

I've altered my 1.5X Kenko KA adapter to "short the A pin", but can't figure out a reasonable way to modify a K or m42 lens base to "short the A pin". I'd appreciate hearing any ideas on reasonable ways to do it.

Jamming tinfoil in works but is not a reasonable long-term approach.

Dave

[Gooshin]

if you have a drill press and some fine bits you can drill a hole in the base of your converter, then press a thin metal tube in

round at the edges using a file (i'm thinking a small snip of a paper clip?)

although a permentatly sticking out metal piece could prove to be destructive...

[newarts]

...

although a permentatly sticking out metal piece could prove to be destructive...

I think such a protrusion would be destructive unless it is spring loaded. I've looked for a such a spring loaded ball assembly but haven't found anything small enough. But I don't know where to look for similar jewelery sized parts.

Are the ball assemblies on roller-ball paint containers short enough I wonder? (I think any hole I drill in the lens mount shouldn't be more than a few mm deep.)

Dave

[Lowell Goudge]

I have modified a K mount to A mount by putting insulating spots for the F stop indications, and by inserting a small spring loaded contact (similar to some computer IC contacts for grid array contacts) into the base of a lens.

Does it work, yes, you can then "control" apature, but there are all sorts of problems.

First of all, the K100 does not use TTL flash, but P-TTL and as a result, even if you can get measured flash, the body MUST think that the lens is at the correct setting.

This might be possible with an M42 lens, because you just tell the camera it is at F1.2 to match the maximum apature perceived by the lack of any contacts tuching the base. The M42 lens will be stopped down to what ever you want, and the sensor reads the light through the lens stopped down during the preflash, and calculates flash duration based upon this. but on a K mount, the body also tries to control the actual apature, and therefore the body influences the apature (it does not open it enough) and wexposure is all over the map.

In my opinion, it is a waste of time playing around with all this, and much better with K and M42 lenses to use a flash with "auto" (i.e. its own sensor) and then enter F stop of the lens, and ISO, to get correct like people did before TTL flash.

[dlacouture]

Hello,

Well, facing the same problem, I've gone the extreme way, and carefully applied solder to the camera's A pin, with really light, gentle brushing motions no more than a fraction of a second long (in order to keep the pin temperature low).
I've tried on a cheap ZX-7 film body before trying it on my k10, of course!

And of course, I will not take responsibility if you completly trash your camera :-)

Now, concerning the PK-m lenses, I read somewhere an useful trick : drill a second locking hole before the original one in order to lock the lens partway in the mount, so the aperture actuator doesn't push yet the aperture lever of the lens... This way, the lens will work like a m42, but will still be able to function as before if you use the original locking hole instead of the new one... Pretty neat, huh?

[Lowell Goudge]

Hello,

Well, facing the same problem, I've gone the extreme way, and carefully applied solder to the camera's A pin, with really light, gentle brushing motions no more than a fraction of a second long (in order to keep the pin temperature low).
I've tried on a cheap ZX-7 film body before trying it on my k10, of course!

And of course, I will not take responsibility if you completly trash your camera :-)

Now, concerning the PK-m lenses, I read somewhere an useful trick : drill a second locking hole before the original one in order to lock the lens partway in the mount, so the aperture actuator doesn't push yet the aperture lever of the lens... This way, the lens will work like a m42, but will still be able to function as before if you use the original locking hole instead of the new one... Pretty neat, huh?

except the camera will think the lens is an f2.8-6 lens as opposed to 1.2-22 lens

you really need to be careful about this especially with a k10 because the metering has problems with manual apature lenses, and while you will have some form of metering, it will be tending to under expose when wide open and over expose when stopped down

all and all, while some people will try this and be pleased, I personally would not.

[dlacouture]

Lowell : of course, these are desperate measures to handle a problem Pentax won't cure in the current Kxx line...

Anyway, that and a LL60, and it becomes quite easy to use old lenses...
Granted, you have to be careful always using f/1.2 on the body, or you'll mess up the exposure...

Talking about the LL60, I'm about to try making a focus screen from a ZX-m split focus screen... Seems odd to me that nobody tried that already, as they were the last genuine Pentax split-screens made, and so maybe the best-suited to the task...
I'll let you know how it goes...

[Just1MoreDave]

A "Ricoh pin" assembly ought to work. I would use the nicely rounded ones from Vivitar or Sigma lenses so they properly retract. These are designed to be electrically isolated but that would be good for testing to see if your idea works. (I am not sure it will.)

[jeffkrol]

Ok 1 question and a puzzle...
1) Though some of you tinfoiled in the real max/min aperture codes the only one really needed is the "A hole"
The data pin is raised so it must make metal contact (except for paint)
Now the thing I'm confused about. With the kit lens I translate the pins as
001-10 which is f4-22....... did I miss something?

[dlacouture]

For modern lenses, actual aperture is sent through the Data pin, that's how the aperture can change with the zoom position...

I'm not sure why they still have the legacy pins... Backward compatibility?

[newarts]

For modern lenses, actual aperture is sent through the Data pin, that's how the aperture can change with the zoom position...

I'm not sure why they still have the legacy pins... Backward compatibility?

SMC-A lenses have no data pin so backwards compatibility is likely correct.

1) Though some of you tinfoiled in the real max/min aperture codes the only one really needed is the "A hole"

That's correct. I checked other combinations for verification of what is reported in the EXIF data.

Lowell says K lenses may only work properly wide open for P-TTL flash.

[Lowell Goudge]

For modern lenses, actual aperture is sent through the Data pin, that's how the aperture can change with the zoom position...

I'm not sure why they still have the legacy pins... Backward compatibility?

Not true

I disassembled a scrap sigma AF telezoom that had variable apature the apature contacts were a sliding switch along the barrel that had the grey scale encoded and a contact set that changed the apature values as you zoomed. It was really very simple.

As a result I believe apature is through the 5 contacts in the base, 2 on one side and 3 on the other side of the A pin. data is lens data, focal length (for zooms) MTF data for program mode and focus data for the AF, it is not for apature.

[dlacouture]

Mmmh...
I was pretty sure I saw some unconventionnal aperture values as I zoomed out with the 18-55 kit lens, but now you mention this, I must be wrong... I'm not such a zoom user myself (apart for my Tamron 28-75 f/2.8 which obviously doesn't behave like this...).

[jeffkrol]

Not true

I disassembled a scrap sigma AF telezoom that had variable apature the apature contacts were a sliding switch along the barrel that had the grey scale encoded and a contact set that changed the apature values as you zoomed. It was really very simple.

As a result I believe apature is through the 5 contacts in the base, 2 on one side and 3 on the other side of the A pin. data is lens data, focal length (for zooms) MTF data for program mode and focus data for the AF, it is not for apature.

hmmm... can't be correct. The f range pins are (as far as I know) just 0 or 1 state.
A code for f5.6-22 does not exist. I also suspect that mechanism you saw changes chip data and sends aperature range through the data bus.
From Mr. Dimitrov
Features and Operation of the Ka Mount
But why does this not happen in the M and Av modes? After all, knowing the positions of its stop-down coupler, the body should be able to calculate how many f-stops the lens is closed down. Knowing the narrowest aperture and the number of f-stops, the body could calculate the widest aperture, and then the manually-selected f-stop. Yes, but only for prime lenses! Variable-aperture zooms have fixed contact patterns, and can therefore only indicate a fixed aperture range. In this case, the incorrect f-stop may be displayed in the viewfinder, and I guess that because of this, Pentax left the feature completely out. Note that due to the TTL exposure metering, the film will be exposed properly regardless of the fact that the f-stop's numerical value may be calculated incorrectly.
They must have "worked around" this a some point but I do not believe it's w/ the 3-2 pins.
After thinking about what you saw in the sigma I would guess that it is a counting pattern.. It will "add" 1/2 stop to max aperature as you zoom. Still you need to add this to some place... Data bus is the only "digital variable" connector I know of. Though a simple use of the "A" pin for this function would be possible as just a "pulse" counter.

[Lowell Goudge]

hmmm... can't be correct. The f range pins are (as far as I know) just 0 or 1 state.
A code for f5.6-22 does not exist. I also suspect that mechanism you saw changes chip data and sends aperature range through the data bus.
From Mr. Dimitrov
Features and Operation of the Ka Mount
But why does this not happen in the M and Av modes? After all, knowing the positions of its stop-down coupler, the body should be able to calculate how many f-stops the lens is closed down. Knowing the narrowest aperture and the number of f-stops, the body could calculate the widest aperture, and then the manually-selected f-stop. Yes, but only for prime lenses! Variable-aperture zooms have fixed contact patterns, and can therefore only indicate a fixed aperture range. In this case, the incorrect f-stop may be displayed in the viewfinder, and I guess that because of this, Pentax left the feature completely out. Note that due to the TTL exposure metering, the film will be exposed properly regardless of the fact that the f-stop's numerical value may be calculated incorrectly.

They must have "worked around" this a some point but I do not believe it's w/ the 3-2 pins.

sorry for the technical term

the contacts are organized such that a simple sliding switch at 1/2 stop increments can update both the maximum and minimum apatures in what is called a "grey scale encoder" technically. This simple switch which reconnects the 5 data bits (pins) as focal length changes is included in the lens.

If I can find the part in my junk bin, I will photograph it so you can see and understand how this works. I bought the lens with the front group missing because I was looking to play with the conversion of a K mount lens to KA

Edit note, in early KA mount variable apature lenses, they simply didn't care because cameras hat TTL metering that corrected for different F stops automatically, and for flash they had true TTL.

the need to have a switch and correct apature came about with P-TTL flash, that is required to know the real apatures for flash calculation.