Pentax KM

I usually consider the K1000 as the successor to the Spotmatic, in fact this one is the true successor (the K1000 has no selftimer or depth of field tester) but it was not produced as long (1975-1977), replaced by generation "M" (ME, MX, MV)
I have difficulties to find the differences between the cameras of this generation, it seems that the KX has also mirror locking capability, and K2 aperture priority automatism.
The lens, 1.8 / 55mm, is the bayonet version of the standard lens of Spotmatic.