The Pentax DA 50-135mm has an average review score of 89%

Score (%):
Pentax SMC-DA* 50-135mm f/2.8 ED [IF] SDM - Review
The Pentax SMC DA* 50-135mm f/2.8 ED [IF] SDM is a high quality medium tele zoom lens but just like its Tokina cousin it is not without flaws. The resolution figures are generally very good to excellent except a drop in border quality at wide-open aperture towards the long end of the zoom range. Based on some real world shots it seem as if it is getting somewhat softer at very close focus distances but then it's not a dedicated macro lens anyway.
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80

Pentax SMC-DA 50-135mm f/2.8 ED (IF) SDM
As one of the first in Pentax‚??s new lens line-up, this optic is impressive. OK, it‚??s not a cheap item, and with no need for in-lens stabilisation you might wonder at the price, but you do get what you pay for and this lens is both well built and specked and produces excellent results. I just hope the others in the proposed line-up are as good.
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NA

Pentax 50-135mm f/2.8 ED AL IF SDM SMC DA*
With this new lens, we're dealing with truly professional gear. I would say that the DA* 50-135mm is the lens the K10D was waiting for. As always with Pentax, ergonomics and ease of use are great. But this comes at a price, in term of weight and size, which may imply a learning curve, and also a stronger bag and a solid tripod. Most important, image quality is excellent.
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98