Pentax 16-50mm F2,8 DA* SDM
Maybe the below comparison review will help
http://www.pentaxforums.com/reviews/pentax-16-50-vs-sigma-tamron-17-50mm/introdu...
Based on that review, I would not upgrade or upgrade to the Sigma equivalent.
Pentax K10D + Vivitar 55/2.8 macro + Super Takumar 55/1.8 + SuperMultiCoated Takumar 85/1.8 + SuperMultiCoated Takumar 135/3.5 + SuperMultiCoated Takumar 200/4 + Super Takumar 300/4
Pentax K100D + DA18-55ALII + DA55-300
Pentax K5 + FA31Ltd + M50/1.7 + DFA100WR + M120/2.8 (+ DA18-55WR at occasion)
Jon
Some occasional random stuff at The Photographers Block: link
The build quality, focus speed and image quality are all better on the Pentax. The only disadvantage if the Pentax is the weight and the length when fully zoomed.
i live mine and the images on my Pentax are far superior to my old tamron images.
PPG Wedding photography Flickr
Concert photography
Currently on a Pentax hiatus until an FF Pentax is released

Thank you for your , advice .
the reason for the upgrade Wim Sturkenboom , isto have a better lens in AF, construction and clear image quality.
My Tamron makes a lot of times the photos, underexposed, and sometimes the colors do not look like real, and my lens Pentax 50-135mm f2, 8 notice that the image quality is totally different from Tamron, Pentax does not need the brakting using the camera, the tamron lot of times I have to change, and failure and AF is slow, despite having a good image quality and with enough detail..
on Schick , in Portugal we need the WR , and the SDM yes it is true is very good , thatīs i need in the lens .
Gary StaffordI hope so because it is already ordered the lens Pentax 16-50mm f2,8 .
best regards for every one .
Jon
Some occasional random stuff at The Photographers Block: link
With regards to underexposure and bracketing, I doubt that that is the lens. I can actually not believe that taking the same picture with 17-50 and 50-135 (both at 50mm and same aperture) will reveal significant differences in exposure unless you have a faulty lens.
Enjoy your new lens

Pentax K10D + Vivitar 55/2.8 macro + Super Takumar 55/1.8 + SuperMultiCoated Takumar 85/1.8 + SuperMultiCoated Takumar 135/3.5 + SuperMultiCoated Takumar 200/4 + Super Takumar 300/4
Pentax K100D + DA18-55ALII + DA55-300
Pentax K5 + FA31Ltd + M50/1.7 + DFA100WR + M120/2.8 (+ DA18-55WR at occasion)
Kind regards .
Wim Sturkenboom Perhaps the lens may be defective, I do not say that the Tamron is a bad lens, but I think a better Pentax lens type sensor, a another brand, but I hope to come to prove it and show here in the gallery.
Jon Schick goes to Faro, which refers to the lens can get, but if you have a kit for a 10-20mm, and a 35mm prime plus a zoon 50-135mm or 55-300mm, can help in very different scenarios you will find in Portugal since the sunset on the beach, the water sports, surfing, all depend the area where, I hope you have a great trip, and who likes to Portugal, if the Lisbon area, or a little further north send a message, maybe we can meet and I'll show some amazing places, ah let's recommendation to visit Cabo da Roca and Sintra area.
Best regards for every one , and thank you for your help

I hired one from SRS, tried it for a few days, sent it back and then placed an order. It's been in the roughest of terrains and pretty extreme climatic conditions. It is my default/walkabout lens. Never had an issue (apart from it sometimes refusing to focus, but that turned out to be a carbon based error by someone in a hurry :$ ).
NSANTOS
Member
FIGUEIRA da FOZ PORTUGAL
I would like to know your opinion about this lens Pentax DA * 16-50mm F2, 8 SDM.
Well read the review on Photozone where this lens has many chromatic aberrations.
The review will be right, because I've read different opinions about the lens, and how is my choice to replace my Tamron 17-50mm f2, 8.
Best wishes
http://www.photozone.de/pentax/405-pentax_1650_28?start=1