Using an M42 or screw mount lens on my Pentax K100D is a fairly same issue as using an SMC-Pentax M lens that i covered in previous post. Metering works just fine like always (one of the primary reason why I lean toward K100D).
But when I “booted up” the K100D with the Vivitar 235, instead of the usual “enter the focal length” screen that greets you when you mount an SMC M lens, it went directly to show the info screen that shows that SR is off. I also found out, that I can only use spot metering. When trying to shoot some picture, It hit me that focus confirmation also wasn’t working. it’s just like the body failed to detect that a lens is attached.
After checking the contact point between the body and the lens, it is apparent that when a lens is attached to a body using M42-to-K adapter, the metal contact point of the body mount does not make a contact with the lens mount surface. If you look carefully there are a small space between the body and the lens mount. K100D, or any Pentax DLSR body detects an attached lens when the contact point on the body “touch” a contact point on a lens, or in case of SMC-M lens, touch the metal base of the mount, sorting all of the contact point on the body.
So? Is there a way to fix this?
One suggestion is to put a thin aluminium foil on top of the contact point on the body to sort all of the pin. You need to make it thick enough so when the lens is attached, the aluminium foil is kept in place by squeezing it between the lens and the body mount.
You can go to Custom Setting on your K100D, and set the “FI with S Lens used”
to “2 Available”
Voila, Metering, SR, Central Weighted and spot metering, Focus Confirmation works!!
These shots below are taken with K100D, Vivitar 135mm F2.8, and AF-360FGZ flash gun