The shadow that is cast by the 16-45 is not due to the 'bulkiness' of the 16-45...but because the 16-45 is quite a wide angle at the 16-20 mm end of it's range.
The pop up flash, on the Pentax DSLR is like most, if not all in that a pop up flash on any DSLR is only good at moderate wide angle settings...say around 28 mm or so.
I have a Pentax 360 flash and a Vivitar 285 HV flash and both have a ''' Fresnel diffuser...that you fit when you are using wider angle lens.
A pop up flash on any camera (DSLR) I'm aware of does not have an additional flash diffuser which will diffuse the flash so that a wider angle lens can get complete flash coverage.
I'm not an expert on pop up flashes and I know Sarah knows a lot more than me on the subject...so Sarah and others, please correct me if I'm wrong.
Last edited by lesmore49; Nov 3, 2009 at 8:11 PM.