ahh...they were both shot at f/8...I am not going to feel too bad....
![Cool](images/smilies/cool.png)
A quick comparison for the OP of these two lenses at f/8 at 135 mm....
http://www.the-digital-picture.com/R...mp=2&APIComp=3
Ok, so I see a difference, but the centers are pretty good at both, still much better for the L. But the 18-135 is falling apart at the edges. So, I suspect we are comparing center crops.
Also, hodnik, do you have a remote shutter release? If not, you may want to get those shutter speeds up or use a count down timer. General rule of thumb is 1/(focal length x 1.6) or faster for hand held. Being on the tripod will help, of course, but you can still get vibration from pressing the shutter release at 1/15 second.