I think I should add some information.
If all contacts are isolated, you can use only M mode with the green button. Handling may be somehow different with the K-01 compared with DSLRs, have a look at the manual.
If all contacts are short-cutted, additionally Av mode will be possible.
I think even the K-01 has (somewhere hidden in the menus) a setting like "enable usage of aperture ring", this should be enabled. As default, for unknown reasons Pentax sets it to disabled. There are no known disadvantages to leave the setting always in enabled position.
EDIT: In Av mode (less frequently in Manual mode) over- or under-exposing with older lenses may happen. The reasons for that have been often discussed in this forum. Possible wrong exposures will vary from lens to lens, and aperture value to aperture value, but are consistant for each of these. You must try out with YOUR lenses, and MAY sometimes need to use exposure compensation. I am lucky - not corrections needed with any of my old lenses.
Last edited by RKKS08; 01-15-2013 at 01:57 AM.