Synthesizes chlorophyll f or chlorophyllide f (Chl f, 2-formyl chlorophyll a), probably by oxidation of chlorophyll a or chlorophyllide a and reduction of plastoquinone. The reaction is probably light-dependent. Chl f absorbs far red light (FRL, 707 nm in 100% methanol), and is synthesized when cells are grown in FRL, where it provides the advantage of extending the spectral range of harvested light in terrestrial cyanobacteria (PubMed:27386923). Chl f synthesis is probably light-dependent (PubMed:27386923). Homodimer (PubMed:27386923). No synthesis of chlorophyll f when grown in FRL (705-735 nm, 26-30 umol photons/m(2)/s) (PubMed:27386923). Due to differences in the C-terminus this protein cannot bind the oxygen-evolving Mn4-Ca-O5 cluster bound by 'normal' PsbA, however it probably still binds plastoquinone and chlorophyll (PubMed:22187288). Belongs to the reaction center PufL/M/PsbA/D family.