Originally posted by séamuis I certainly cant say for sure but im 99.9999% positive the plastic mount is referring the new L versions of the 18-55 and 55-200mm DA 'kit' lenses. same great optics, just a cost cutting measure to keep the price as low as possible for entry level and beginner DSLR buyers. though personally I don't agree with this decision, especially since the normal DA 'kit lenses' can be had for very cheap. just doesnt make sense to me to implement a plastic lens mount. i dont think it will go over to well.
How much do you reckon the actual production cost of the kit lens is?
Answer: It is very cheap to make.
Like you I think a metal mount is preferred and stronger but there are cost savings in not using a metal mount, even though it may cost very little.. Small savings add up margin wise.
Secondly, using a plastic lens mount is not a new thing for Pentax. Some of the el-cheapo Pentax FA zooms already had them years ago. Nikon, Canon and a few others have been using plastic lens mounts for their beginner level lenses for many years already. In fact practically the entire Nikon kit lens is made of plastic, including the lens elements. So why should Pentax be any different here?
Beginners, oldies, ladies, kids and many gear geeks clamour for compact and lightweight equipment, even at the expense of robustness. We're now in a throwaway society, the consumer today wants something to work that's cheap. If it breaks, it is easy to get another because it is not worth it to repair.
That's also a strategy for the camera manufacturers to get new users on an upgrade path. The kit (for some s*it) lens is to tie them over until they start to buy better performing and better build lenses that cost more.