With the subject of new lens mounts in the future, a common definition
of lens compatibility would be a good thing to avoid all sorts of
confusion and half truths.
There are 3 types interfaces in a modern lens mount:
1. mechanical - how the lens physically attaches to the body
2. information - how the body knows what kind of lens is present how the
lens is set
3. control - how the body controls what the lens does
How these interfaces are changed effects body/lens
compatibility/functionality. There are 2 basic types of compatibility:
forwards and backwards. Forwards is putting an old lens on a new body.
Backwards is putting a new lens on an old body.
What does this mean in the Pentax realm? Any K mount lens can be
physically mounted on any K mount body: this is type 1 physical
interface forwards/backwards compatibility. Type 2 and 3 categories
depends on body/lens specifics. A K mount lens can't be mounted a a
screw mount body, but a screw mount lens can, with an adapter, be
mounted on a K mount body. So there is no type 1 backwards
compatibility, but there is forwards compatibility.
Other brands
Minolta and Canon AF and MF lenses/bodies pretty much don't share any
interfaces (whatever adapters exist require optical elements, and even
then it's only type 1). Nikon can be complicated. Nikon SLRs started
with the F mount and still have the F mount, but this is only a type 1
interface. Changes in the type 2 interface has effected the type 1.
Short story long: the newest Nikon lenses can be mounted on the oldest
bodies, but mounting an old (non AI) lens on a modern (AI) body can
damage the body. Type 2 and 3 interfaces have had more changes and
variations with Nikon than with Pentax.
So, when folks make comments about lens/body compatibility, they have to
be specific about what aspect of the interface they are referring to, if
the comment is supposed to make any sense.
BR
