Ron Guth: In 1813, John Reich modified the obverse of the Half Eagle by eliminating Liberty's decolletage, enlarging the head, and altering the size and shape of the cap. Reich made fewer, less obvious changes to the reverse, but the structure of the eagle's wings is definitely different, as is the positioning of the arrows. Technically, this new type was issued until 1834, but a big change in 1829 requires recognition. Prior to 1829, Half Eagles were struck in what is known as an "open" collar -- one which was used more to position the coin than to serve as a third die. This was changed in 1829, when a "close" collar was introduced for the Half Eagles. The close collar produced a uniform diameter on all coins struck thereafter. In order to accommodate the new technology, slight modifications were made once more to the dies, mostly in the size of the lettering and the shape of the denticles and outer border.
This type is replete with rarities, including the 1815, 1822 (3 known). Most dates in this series started with low mintages and were decimated later each time the value of the gold they contained exceeded their face value. Despite the rarity of the coins in this series, a surprisingly high number of Mint State examples survive. PCGS (as of May 2011) has certified 659 examples of the 1813-1829 Small Diameter type, of which 402 are Mint State (exactly 61%). This indicates three things: 1) most of the circulated examples were culled from circulation years ago, 2) those that survived are impaired and ungradeable, and 3) numismatic activity saved nice coins from destruction. The finest Mint State examples certified by PCGS (as of May 2011) include nine MS-66 examples. Proofs of this type exist but are exceedingly rare. The quality of the Proofs varies from convincing Gems to "one-sided" Proofs, where one side is clearly Mint State but the other is Prooflike or Proof.