I would think that the body could potentially compute the approximate current aperture setting based on the amount of light before/after the stop-down metering. It's kinda a hack, though.
I don't mind the lack of coupling too much. It does complicate operation a bit, but for someone like me that likes to tweak stuff, it means the older lenses will stay cheaper.
I am curious how much additional expense it would be to add coupled-metering to a body. For the expensive models, it might be an acceptable expense.
-Cory
On Tue, 12 Apr 2005, Anthony Farr wrote:
Cory,
At the bottom of that web page is the following:
"NOTE: This modification will not permit shutter-preferred or programmed autoexposure and will not allow K and M lenses to be used on the new *ist and *ist-D cameras (or the ZX-30/MZ-30, ZX-50/MX-50 or ZX-60/MZ-60)."
Since that web page was created Pentax released a firmware upgrade to allow the *istD to do stopdown metering with the green button, and the *istDs was released with that ability (via a different button). But when the istD was released it could only meter with pre-A lenses at wide open aperture.
You're correct in thinking that it's a gear limitation preventing the conversion from working, but it's not in the firmware - it's in the hardware. The cameras named don't have a mechanical relay for the aperture setting, they depend upon electrical data relay only. The mechanical relay is a legacy of the original K-mount of c.1975. The A lenses introduced the electrical contacts between camera and lens, but for the sake of compatibility the two systems co-existed in cameras and lenses for some years until Pentax finally began to drop mechanical linkage on cheaper models.
But when the *istD appeared without mechanical linkage there was a great wailing and gnashing of teeth, because this was not a budget camera to be dismissed as a newbies' camera. Pentax had sent a message that it would not maintain full backwards and forwards compatibility forever.
regards, Anthony Farr
-----Original Message----- From: Cory Papenfuss [mailto:[EMAIL PROTECTED]
Hey all... I've been playing with some older lenses I've got with my *ist-DS, and I figured I'd try my hand at modifying a lens to have the electrical contacts. Basically, the same modification as outlined here:
http://www.robertstech.com/matrix.htm
After successful completion of drilling jigged divots, I still cannot get anything other than center-weighed metering. Upon further examination, it appears that even on an official KA lens with insulators, if the aperture ring is set to other than 'A', center-weighed metering is used. Looking through the manual, it says that multi-segment metering requires a 'A' lens or greater, but doesn't actually say it must be *set* to 'A'. Is this a limitation in the firmware on this model? Apparently on some bodies (like Mark's) it should be possible once the contacts are set to inform the camera what aperture ranges it can do.
-Cory
************************************************************************* * Cory Papenfuss * * Electrical Engineering candidate Ph.D. graduate student * * Virginia Polytechnic Institute and State University * *************************************************************************
