If you want to use a non-AI/AIS lens on the F2AS, the meter coupling lever has to be pushed over to the left (looking at the camera front). To return it for using Ai/AIS lenses press the return button. See:
Coupling Lever Lock/Release Operation
"The camera's Photomic finder is fitted with a meter Coupling lever that provides for coupling between the finder's metering circuit and the lens' meter coupling ridge. When the camera body is used with lenses offering automatic maximum aperture indexing, the lever remains in the normal position.
However, when the camera body is used with lenses and/or accessories not provided with this feature, the lever must be locked up to permit exposure measurement via the stop-down method.
To lock up the lever prior to mounting the lens, simply push upward and to the right until the lever clicks and locks into position. To release the lever for operation with a lens or accessory capable of automatic maximum aperture indexing, simply slide the coupling lever release (located just above the lever) to the right until the lever returns to its normal lowered position; then, mount the lens as explained previously."
Hope that helps.