The Lomo guys created a new interesting convertible Lens System. You can finance their idea on Kickstarter:
The Neptune Convertible Art Lens System consists of a lens base that’s mounted to your camera and several convertible lens components. By interchanging the front components, you can shoot photos or videos at three different fixed focal lengths — 35mm, 50mm and 80mm. An Art Lens System unlike any other; it offers you all the freedom of a zoom lens without compromising on prime lens quality, and it’s the only convertible Art Lens out there to work with a range of modern-day analogue and digital cameras. Each component is assembled by using the finest multi-coated glass and crafted to produce exceptionally sharp focus and strong, saturated colors for stunning high-definition images — even when you’re shooting close-ups at 0.25m/9.8” with Thalassa (35mm), 0.4/15.7” with Despina (50mm) or 0.8m/31.5” with Proteus (80mm). This is an Art Lens System that lets you take beautifully intimate shots, allowing you to get near enough to capture every last detail of your subject. And because it’s so small and lightweight design, you can take it with you everywhere.