Michel Carrère-Gée <[EMAIL PROTECTED]> wrote: >http://www.robertstech.com/pentax.htm >Propose us to modify the M&K lens to permit the matrix metering >Some what consists this modification ?
To enable matrix metering on cameras that have it, the lens needs to tell the camera its minimum and maximum apertures. This is achieved with a series of conductive and non-conductive contacts in the lens mount flange that short out (or do not short out) contacts in the lens mount of the camera. These are among the 7 contacts in the lower left-hand section of the lens mount of the camera which you can see when you remove the lens. One of these contacts transmits digital data from autofocus lenses and is not used for matrix metering. Another one tells the camera if the lens is set to "A" for shutter priority or program autoexposure; this one also has nothing to do with matrix metering. The remaining 5 contacts are where the min/max aperture data necessary for matrix metering are conveyed. On "A" series and later lenses, there are plastic insulators in one or more of the positions corresponding to these five contacts. If there's a plastic insulator, that contact is open. If there's no plastic insulator (bare lens mount), the corresponding contact on the camera body is shorted to ground. The pattern of which ones are grounded and which aren't tells the camera body what the maximum possible aperture is for the lens (and also what the minimum aperture is). On a 50mm f1.4 there's only one insulator and on a 400mm f5.6 there are four. A 20mm f4.0 and a 300 f4.5 both have three, but in different arrangements. This is the information that allows matrix metering to work. Basically, I drill a slight divot in the flange of the lens mount at each position that needs to be insulated, corresponding to the pattern appropriate for the lens in question. Then I put a drop of epoxy paint in the divot. It's a very simple procedure, but it requires that getting the divots in just the right locations. I've built a jig that allows me to get them exactly where they belong with a minimum of fuss. As a measure of my confidence in the procedure, the first lens I tried it out on was my K-series 15mm f3.5 and I'm very happy with how it's worked out; I find matrix metering especially useful with wide angle lenses. If you ever want to restore the lens to its original condition, all you have to do is replace the lens mount flange, which anyone can do with a couple of jewelers screwdrivers. I think the plain k-mount flange is still available from Pentax, but even if it's not there are millions of M50/2.0 lenses that can be had for a few dollars to become parts donors. You can email me dirctly, but you'll have to sign up for Hotmail or some other free email address because wanadoo.fr is blacklisted form my domain because of extensive spam problems. -- Mark Roberts www.robertstech.com Photorgaphy and writing
