On Aug 22, 2009, at 17:29 , gldnbearz wrote:
Is there a way to block the SDM contacts for an over-ride?
All the digital data between the camera and the lens uses one single
pin. If you block that pin, you will have an unknown manual lens.
The other pins (and an illustration) are explained on Boz's site. Text
from that page:
The KA mount requires body-lens communication that cannot be
accomplished via the mechanical couplings of the original K-mount.
First, in order to know when to use the Tv or P operating mode, the
body needs to be able to determine if the lens aperture ring is set to
"A". Second, after the body measures the scene's brightness and
determines how many stops the lens should be closed, it must know if
the lens can be closed that many stops. Finally, in the Tv and P
operating modes, the higher-end KA bodies display the picture-taking f-
stop in the viewfinder. In order to support this feature, the body
needs to know the absolute value of the lens widest f-stop.
Pentax implemented all of the above functionality by adding six
electrical contacts to the flat surface of the body and lens mounts.
These contacts are located in different positions from those of the KF
mount, and therefore do not lead to any incompatibilities.
On the body mount, the "*" contact is slightly recessed. On the lens
mount, "*" is a small pin whose head can be raised or lowered
depending on the position of the lens aperture ring. When a numeric f-
stop is selected, the pin's head is lowered so that it does not make
contact with body's "*" contact; when the "A" aperture setting is
engaged, the pin's head is raised, and it makes electrical contact
with the body's "*" contact.
The remaining five contacts are easily seen on the body. They look
like small, slightly-protruding, ball-bearings. The lens-mount
contacts are of two types: conducting and non-conducting. The non-
conducting contacts are small plastic circles. The conducting contacts
usually cannot be seen, because it is the (metal, and thus conducting)
mount that fulfills their role. In rare cases, the lens mount has five
holes, some of which are filled with plastic, and some with a golden
metal. The golden metal and the plain "mount" contacts seem to have
identical functionality.
Inquiring Minds Want to Know
The conducting/non-conducting pattern that the lens contacts form is
decoded by the body as the lens' narrowest aperture and number of f-
stops. George de Fockert deciphered the pattern by cycling through all
possible combinations on a ProgramA in program mode and looking at the
minimum and maximum apertures shown in the viewfinder.
The table below shows the lens contact patterns in the following order
r1r2m1*m2r3 where each contact is either metal (represented by 1) or
plastic (represented by 0).
The page: http://www.bdimitrov.de/kmp/technology/K-mount/Ka.html
Joseph McAllister
pentax...@mac.com
“ It is still true, as was first said many years ago, that people are
the only sophisticated computing devices that can be made at low cost
by unskilled workers!”
— Martin G. Wolf, PhD
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