Cory's correct, the A pin is shorted to ground in the A position. Different lenses do this one of 2 ways: 1.) The pin is always grounded and "sticks out" when in A. 2.) The pin always sticks out and is grounded in A. Same difference.
I have simulated the A pin being grounded by simply putting a tiny "pellet" of aluminum foil in the A recess on the body and carefully mounting the lens. This gives the body aperture control. With the proper recesses drilled in the lens mount to tell the body what the Min/Max apertures of the lens are this actually does work on the D. You set the lens to its minimum aperture and shoot just like it was an A lens. Any exposure mode you like. THE PROBLEM, as has already been mentioned, is the actuator lever on the lens. In K and M lenses all this lever does is travel ALL THE WAY in one direction or the other, it has no need for linearity as it is the aperture ring that determines how far the aperture closes. With my modification above some lenses work well, others give incorrect exposure. Considering the effort involved in correctly drilling the lens mount, and the fact it seldom works as desired, it really isn't a very useful procedure. It was fun to try though. ;-) Don > -----Original Message----- > From: Cory Papenfuss [mailto:[EMAIL PROTECTED] > Sent: Thursday, May 26, 2005 7:19 AM > To: [email protected] > Subject: Re: "A" need > > > On Thu, 26 May 2005, Mark Roberts wrote: > > > "Collin Brendemuehl" <[EMAIL PROTECTED]> wrote: > > > >> is a body modification that will allow the "A" connection to > be turned on > >> within the body. Perhaps a piece of foil to short the pin to the mount > > > > Shorting is the normal condition for the "A" pin. You need to *insulate* > > it from the lens mount to fool the camera. If you did so with a K or M > > lens you wouldn't be able to meter properly on the ist or ist-D. > > > > -- > Actually, as I look at it, I think he's (almost) right. Shorting > the pin to ground tells the camera it's 'A'. The difference is that the > pin is *recessed* on the camera. In order for the lens to short it when > set to 'A', the pin comes out further than flush on the lens to make > contact with the recessed pin in the body. > > Even if you phonied this up, it wouldn't meter correctly. The one > possible way this could work is in the manner I described in my other > post. Basically: > > - Modify the K lens to have the 'A' contacts... including the spring > loaded one that comes out further than flush to activate 'A' mode. > - In 'M' mode, dial up the same f-stop as what the lens is set to. > > This would only work correctly if the distance the aperture > actuator lever moves in 'A' mode is as far or farther than necessary to > actuate the 'K' lever to where the lens's internal stop is set. > I haven't > figured out what the log/linear distances would be and if it's possible. > > There are a lot of issues with the scenario. It would be a *LOT* > simpler if the camera would just allow you to manually set the > f-stop when > using an A lens in non-A mode (i.e. a modified K lens). > > Phew... that was ugly... :) > -Cory > > ************************************************************************* > * Cory Papenfuss * > * Electrical Engineering candidate Ph.D. graduate student * > * Virginia Polytechnic Institute and State University * > ************************************************************************* >
