Originally posted by Jonathan Mac I use the numerical score of a lens to know if I should outright dismiss a potential purchase, assuming that there are enough reviews to make the score statistically significant. If it gets past this dismissal stage then I read the reviews and look for common threads - good at this, bad at that - and use that to assess if I think it will do what I want it to. The numerical score isn't useful for that. It's a case of qualitative data being far more useful that quantitative data.
I have thirty lenses all PK mount and I agree with you on this observation. Looking through my complete table of PF ratings, I can offer the following thoughts:
1. Any prime with a score greater than 9 I have enjoyed using
2. Any prime with a score less than 8.5 has taken quite a bit of familiarisation (e.g. the K24mm) or has been a bit of a disappointment (M135mm), except for my Vivitar Komine 135mm
3. Only 4 of my zooms scored above 9 and all have been delightfully sharp - Pentax DA 16-85mm and 55-300mmPLM, and two SP Adaptall 2s - 35-80mm and 60-300mm
4. Zooms scoring below 8 have generally been rubbish and those between 8.5 and 9 need careful use.
However the ratings are not sufficiently controlled to be a ranking tool or an outright decision-maker. As Jonathan says, you then need to go to the qualitative descriptions and look at when it was scored, on what body, film/digital etc. Only then consider a potential purchase. It's a lot harder to do online than with a local seller, but I have never been disappointed with an online purchase of any lens rated above about 8.6 (Only primes, I do not feel comfortable buying zooms online, possibly excepting cheapies from MF era). Certainly with anything rated below 8, I would not even bother to check out a local seller (the dismissal stage is triggered by a rating below 8).