Ever been out shooting with one lens? Just one focal length. No zoom. No wide angle. No telephoto. Just a normal lens. If you're going to try it, (and you should) you could do a lot worse than this. The 40mm f2.8 Zuiko on an Olympus Trip 35, produced from 1967 and 1984. No batteries, thumb-wheel film advance, zone focusing, auto exposure plus un-metered manual (any aperture you like at 1/40). Basic but functional. Everybody had one and David Bailey appeared on the TV ad. "It's got a Zuiko lens" he said. What more do you need? Well, the meter on mine went iffy a few years back, but I've read that you can jam the shutter to the more useful 1/200 speed with a paper clip, then use manual aperture selection to make it the ultimate stealth 'street' camera. £5 should get you a good one. Who needs a Leica?
