I wrote a small java applet for merging image crops together. I hope some of you will find it useful and create a few images of lenses I don't have. The tools are available at
weblightbox. The pixel stacker (also known as measurebator) was used to generate the images below.
Here's a brick wall test between the Pentax 21mm f/3.2 Limited and the Tamron 17-50mm f/2.8.
The Pentax 21mm f/3.2 Limited is one of my favorite and most used lenses. The size and focal length make it great for backpacking and travel. I haven't used the Tamron 17-50 f/2.8 very much, but it seems like a good option for weddings and similar situations.