Originally posted by FishrOfGrizz On the aperture ring next to f22 there is an A (colored green)
As noted above, "A" on a K-mount lens means that the lens has electrical contacts on the base to support aperture control by the body. The is a good thing because it means that the lens supports all all exposure modes on modern Pentax dSLRs as well as all Pentax-brand K-mount film bodies. There is one small caution, however, that pertains to third-party makers such as Tokina. It was not unusual to include not only Pentax mount contacts, but also a small pin to support Ricoh's program exposure cameras. The so-called "Ricoh Pin" is located at the same position on the mount as the AF drive cog on Pentax auto-focus bodies and creates potential that the lens may become stuck on the camera due to interference with the AF cog "well". That is why it is often referred to as "The Dreaded Ricoh Pin".
There are two varieties of the Ricoh Pin. The more dangerous is a square cut round pin. Less hazardous is a round-topped version. Several users on this site (myself included) have successfully used lenses with the round-topped pin. Both types should be considered with caution. Clues to whether the pin might be present are:
- Ricoh/Rikenon "P" lenses with green "P" on the aperture ring
- Third-party K-mount lens with "A" and/or "P" position on aperture ring
- Markings on base or barrel: K/R, PK/R, R/K, KA/R, etc.
- Goggle "Ricoh Pin" for diagrams showing location of the pin
It is possible to surgically remove the pin on offending lenses rendering them harmless.
Steve