1952 PF66 CA Lincoln Cent

Ahh...proof set "early years". Due to die preparation, there were not a large amount of cameo coins coming out of the US Mint in the early 1950s (and for the most part all the way up until the 1970s). As the dies wore down from continuous striking, the cameo characteristics became weaker, revealing a brilliant finish for most coins. These days, technology has improved the dies so most all proof coins coming out of the US Mint have ultra cameo characteristics.

To learn more, please see Rick Tomaska's book on cameo coins from the early 1950s-1970s. An excellent resource.

Check this recent addition out.