Originally posted by Wildfire_ja One last thing.. previous poster.. Please correct me if I am wrong (and I recognize I'm probably wrong), but if the flash is "interpreting" the focal distance for APS-C it should zoom to 75mm for a 50mm lens. The multiplier is 1.5
That is what I understand... but I really could be wrong. Perhaps you too will need to contact Pentax to get some answer
You're thinking about it backwards. The flash doesn't really have a focal length like a lens. It just has a reflector which focuses the light at different possible angles. By industry convention (for whatever reason!), there are standard flash zoom stops at positions that cover approximately 74°, 65°, 54°, 40°, 29°, and 24°. (Give or take.) These angles of coverage happen to correspond on 35mm full-frame to 24mm, 28mm, 35mm, 50mm, 70mm, and 85mm. On a 1.5×-sensor dSLR, the same field of view is covered by a 1.5× shorter lens — so the flash displays numbers 1.5× smaller.
When you put that 50mm lens on there, it should display 48mm — that's the 29° zoom point in 1.5× crop terms, which is the narrowest point which still covers the focal length of the lens. (Makes sense — just a few mm wider than the actual focal length.) The surprise comes when you put a 70mm lens on there — turns out, 58mm is as narrow as the flash can go — it's the 24° point.
Does that make sense?