I was trying to work out what focal length lens I need to photograph at a dance event. It basically came down to which lens would let me capture people standing up from a given distance. So I did the maths, and drew a chart. Along the bottom is lens focal length (in 35mm equivalent) and up the side is the distance from the person that you need to stand. I've used a 6' person as a guide, but distances are in metres and focal lengths are in mm. Worse still, the x axis is logarithmic to make it fit on a page. So.. using the Panny 20mm lens you'd need to stand just over 3 metres away to get someone's full height into your picture. Using the Oly 75mm you'd need to stand 12m away. Using the longest native lens available (i.e. 300mm) you'd only have to be around 46m away. For my dancing query this is causing a quandary. For informal dancing 3m is a good distance - near enough to avoid people getting in the way of the shot, but far enough to be clear of the dancers. For competition, 5-10m at floor level or 15-20m if you're on a balcony is needed. Given a fast lens is needed for the indoor no-flash shooting I'm going to take a risk on the Oly 75 and wait for the crowds to clear before shooting informally.