Originally posted by Qwntm Yes, the distance is shorter with no mirror. I actually have a $10 Pentax to Fuji x Adapter right now that works great.
So no, Pentax going mirrorless is not the end of using the K lenses, but it might be the end of any new K mount lenses. The plus side would be that all the new ML lenses would be new and modern and expensive.
It's never going to happen unless some one high up at Ricoh has a come to Jesus moment, so nothing to worry about, but fun to think about!
The thing is, it doesn't have to be shorter, but it can be.
The shorter registration distance brings benefits in lens size at shorter focal lengths, but increases the angle of incidence of the light rays at the edges of the sensor (something that can be allowed for as far as the sensor microlenses go, but presumably requires a compromise for longer focal length lenses), and which requires more correction for lateral chromatic aberration, so it doesn't necessarily make the lens design much less complex than a retrofocus equivalent for DSLRs, even if it can still be smaller overall. I presume you know all this, anyway.
My point is that a mirrorless body can still use the K-mount – it just takes some clever styling to accommodate the extra registration distance without making the body appear too bulky, something the K-01 failed to do, even if some people thought it looked OK (most didn't, although I think that could have been largely overlooked if they'd fitted an EVF to it). The overall size of lens/body combinations would suffer a little on the wider end, but not significantly on the longer end, and the additional weight penalty would be small. The major benefit to Ricoh would be that they wouldn't have to run two separate lens mounts (three, assuming there'll be a continuation of the 645 line).