In praise of primes - which next?

I think 50mm was regarded as a better FL on 135/FF, but the flange distance of 45ish mm on SLRs meant it was easier to design a 55mm lens.  When SLRs first came out 55 was a common FL but the makers gradually moved to 50.

There are various theories about why these FLs were thought best but I've never been convinced by any of them.  My guess (and it is only a guess) is that early cameras had very simple optics in bassic bodies that just had whatever FOV came out.  People got used to that FOV so when more sophisticated cameras came along that FOV seemed natural.

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Gerry
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First camera 1953, first Pentax 1985, first DSLR 2006
http://www.pbase.com/gerrywinterbourne