Originally posted by Ruspast Summarizing your comments, I would say the Tamron has the lead - it has the IQ and the reach and the people who have this lens like it (at the same time knowing and willing to live with it's limitations) and recommend it. The Pentax 50-135 has no detractors, but I am used to longer reach (I do understand the weight factor quite well). It is also true that many pros I know use full frame cameras and thus the Pentax 50-135 on an APS camera is equal in reach to their full frame Canon/Nikon 70-200. I plan to consult with at least one of them who specializes in church photography (BTW I am NOT a wedding photographer and the church where I am the staff photographer has no pews) in reagrds to the focal length. It seems the Sigma 70-200 has the best AF, but IQ/copy are of immense importance and are a "hit or miss." There were not too many fans of the Sigma among those of you who replied. So at this time I am more likely to risk buying either the Tamron (its price is about $750) and hoping it works, or the Pentax 50-135 (that runs about $850). With the latter I can either sell it if it doesn't work, or get a prime 200mm/300mm later.
I believe Tamron has a 6 year warranty, so if the lens is not acceptable send it to them and have them bring it into spec. For the money I would go Tamron.
If speed and money are not an issue the Pentax 60-250 f/4 is an excellent lens. This would be my second choice as the IQ is excellent and you get a bit more reach, but it is only an F/4 lens...... and it costs 2x as much as the Tamron.
Tamron looks pretty damn good.