<p>If you have a 17-35mm lens then it's good for architectural works. Just keep some extra space around your subject to be corrected ( perspective ) later in Photoshop. The best to use a 17mm or 24mm perspective control lens. </p>
<p>You can blow away dust particles with a lens blower. But for greasy/oily spots on lens glass you need lens cleaning fluid. Try the Eclipse Lens Cleaning Fluid. It's really good.</p>
<p>Harry, defragmented histogram causes because of the lack of smooth tonality in an image. Very hard to see the difference between the two ( healthy vs defregmented ) with a monitor but it suffers an image (less tonal range) when it is printed.</p>