I have this lens and the the lens can zoom by it self (gravity) because it works so smooth. The macro position is only available in the 70mm position and locks the in the 70mm position. So you can focus but you can't zoom
The image is about the same size as in the 210mm at closest focusing distant.
Zoom-creep is not funny when taking macro pictures and pentax avoided that this way.
On the net there are rumors that this lens woul not have a constant aperture, I checked on a white wall and found that my camera (samsung gx20) gives the same exposure time from 70mm to 210mm.
In a practical situation exposure time wil differ due to the fact that zooming in usually means less sky.
This lens came with the 1.7 50mm that I bought (also included a program A film camera).
At the moment I don't use it sice I have a 50-200 WR wich is a lot lighter.
But as soon as I have a K1 I wil use this one.