I took delivery of a new Pentax smc DA* 300mm f/4 ED (IF) SDM lens today. I have heard such good reports about it that I have been promising myself to get one for ages and ages so this week, I took the plunge. I went out and about to give it a work out but the weather was very dreary and dull so it wasn't really a good day to test it.  My first impressions are positive. It's small and very light in comparison to my Prime 500. It is a very solid and easy to use and  focused very quickly and silently.  Its light enough to use hand held which will be a real bonus for some situations.  The only picture that I took today (literally) ws this robin in a very dim place but even with a high ISO of 1000 I am very pleased with the result.