I had a Silette with Apotar lens for many years but I think it was f3.5 When I became keener on photography I got rid of it because I didn't find the lens that good, though part of the trouble may have been that the colour negative films of the 60's and 70's (mainly Agfacolor CN17 etc) which I was using weren't themselves capable of very high resolution. The best lens on a Silette was the Solinar. Anyway best of luck with yours!