Originally posted by Jonathan Mac The 75-150 is definitely worth getting, especially as it's usually available for around €30.
I don't like any of the M 28s I've tried (f/2.8 (both versions) and f/3.5) but the f/2 may be the exception, but in eight-or-so years of being a Pentax shooter I don't think I've ever seen a single copy for sale.
The 40mm gets mediocre reviews and usually sells for far too much, while the 50/2 also gets mediocre reviews and has zero advantages over the f/1.7. I'll stick with the 50/1.7 (I have three of them) which is superb and barely bigger than the 40mm. The 1.4 is nice to have too if I really want the extra speed.
I have to admit that the M series does contain a few duds, so I'd never set out to get them all.
My reason to buy M*s has chanced over time. At first it was to get my K30 working after aperture block failure as cheaply as possible. Then as manual glass draw me deeply into photography, I started to buillt a kit of the best lenses in M series. Now I've been filling the gaps to get more lenses to shoot in single in challenge. So I'm acquiring also the cheaper version of focal lengths and not so highly graded focal lengths. I've come to conclusion that, if I shoot 2 months with each lens and nothing more, they are well worth the money I need to invest. Especially if I sell them of afterwards.
I think that M28's problem is that M35/2 is better. I like my 28's, but due to more versatile 35 i don't need them in my travel kit. At least while I shoot APSC. On FF the difference in focal length might be more significant.
Agree on 40 & 50/2 based on reviews. Not really interested in them, but I'll see them thru anyway. Maybe I learn something. If nothing else, I can form an opinion based on own experience. I've only taken few shots with 50/1.4, but for wide open performance it seem's to be a better choice.