Originally posted by derelict All of this without losing the 2.8 speed of my 28, as a lot of shooting is done in early morning light where being able run a decent shutter speed is important. The 15/ 4, from what I have seen is good but I am afraid that it will not be fast enough.
No problem, it's effectively as fast as your 28/2.8.
To avoid shake (without SR), you need at least 1/30 sec with the 28mm.
But with the 15mm, you can go down to 1/15 sec for the same amount of blur.
(I've handheld it at 1/2 sec with SR.)
Pentax knew what they were doing when they designed the DA Limiteds.
Moving from 15mm to 70mm, they progressively increased the speed:
15/4, 21/3.2, 35-40/2.8, 70/2.4.