Pancake Lenses got their name for a reason: They’re super-flat. Skinny means light, too. The Zuiko 25mm f/2.8 weighs only 3.35 ounces. Why? Thank its dual-sided aspherical glass element. The Olympus Four Thirds sensor format makes this the equivalent of 50mm on a DSLR, Four Thirds, or Micro Four Thirds body. And its images are far from flat.