Originally posted by MrB1 I bought the 28-105 for use on APS-C (K-5IIs and K-70)
Yes, good idea. When I was shooting landscapes with the K3. When hiking, sometimes you want to frame a chain of mountains far away, or zoom in some forest partially covered with fog, 50mm or even 70mm are too short. And carrying another long zoom / prime is too large / heavy. The DFA100 is an option, but we have to swap lenses, not so convenient is the weather is rainy or windy. Having both 28mm and 100mm is already a good range, very usable on apsc, and also full frame compatible in case of a future upgrade to a full frame camera body (when the K1 will be cheaper for instance).