On 18 Jan 2012, at 17:38, Mark England wrote: > 80 minutes total exposure, as 40 successive 2 minute exposures. The key to success is the light pollution filter, which blocks out all the orange glow from sodium vapour street lamps. Aha, I do have one of those. Tim -- The Wellcome Trust Sanger Institute is operated by Genome Research Limited, a charity registered in England with number 1021457 and a company registered in England with number 2742969, whose registered office is 215 Euston Road, London, NW1 2BE.