Olympus glass is out of this world. literally. The camera onboard the International Space Station is manufactured by Olympus. If this lens cost twice as much (like many equivalent Nikon and Canon lenses) it would still be a bargain. The numbers 9 and 18 indicate the magnification range. , from 9mm to 18mm. 9mm is referred to as wide or ultra wide. Compared to older lenses used for 35mm cameras, this lens has a focal length range of 18mm to 36mm. This is an exceptional lens that has very little distortion even at the widest angle. Chroma, which is only present at the very edges, is virtually non-existent (I've compared chromatic aberration with my $1,100+ lenses and found no difference). If you shoot a lot indoors, this lens is for you. If you often photograph architecture, this lens is for you. It's even good for landscapes and makes great panoramas (if the landscape isn't too far away). I like this lens as "people"; You can hang the camera around your neck and shoot from the hip almost anytime. You don't have to look through the viewfinder. Whether in the sun or in the shade, even without using autofocus, this lens focuses from 1.20m to infinity, which means you can photograph crowds of people walking between them. The person you see standing a meter away from you? Yes, her whole picture from head to toe in the frame. As an outdoor lens, it gives a very intimate view of life.