Mark, this info would be most EXCELLENT as a web page. (hint, hint) Dan Scott
On Wednesday, September 18, 2002, at 06:31 AM, Mark Roberts wrote: > 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 > >
