Originally posted by aremmes The equivalent would be the DA 645 28-45/4.5. With an 89° diagonal field of view at 28mm, it's one degree wider than the DA 15 Limited.
I think the idea was equivalent to 16-35 on full frame. 28-45 is far away from that, it is 22-35 on full frame.
To answer the question: No, there will be no 20-45mm for Pentax 645. Because you can't reach the high optical quality the 28-45 offers even wide open, when doing such a big zoom range in the wide angle region. There might be a 20-28/4.5 or similar one day, off course. But again as big as the 28-45, at least, and at least as expensive.
By having to discontiue the 25mm, the 645 sysem lost quite a lot of its wide angle abilities. Not only because it was 19mm full frame equivalent instead of 22mm (rounded), but also in case even this was not enough, at least the Japanese version was for full 4.5x6, so by taking a film body with you, too, there was the option to get even 15mm FF equivalent. Off course with the other characteristics film has.
In my opinion on the day they knew the 25mm will have to be discontinued, they should have put a 20-28mm on the roadmap.