My primary lens (Canon 17-40mm f/ USM L) is such a workhorse. I use it all the time which means it is regularly cleaned. I have another lens that I use only occasionally and so it is frequently dirty when I pull it out of my bag. When working with lens flair (or just shooting into or around the sun with a wide angle lens) it is crucial that your lens be spotless. From the photos above you can see TONS of lens flair elements on the top image - if you need help seeing them look at the photo below.
The small dots around the faces are retouch marks - the larger cicles represent all the lens flair I removed from the image. I could have saved myself so much time and headache if I had cleaned the lens before using the lens. The next time you look in your bag and see a lens you haven't used in a while - take a second, pull it out and clean it. When you need it later you will be glad you did. Your lens should not be a candidate for an Orbit commercial. Dirty Lens? -- Clean it up!
Camera: Canon 20D Lens: 18-55mm f/3.5-5.6 with (dirty) wide angle attachment
Settings: 1/80 f/11 ISO: 100
Light: Lastolite tri-grip diffuser being held out of frame camera left to cut the hard sun light by my assistant.
Settings: 1/80 f/11 ISO: 100
Light: Lastolite tri-grip diffuser being held out of frame camera left to cut the hard sun light by my assistant.