SMC Pentax-FA 77mm F1.8 Limited

Design Philosophy of the FA Limited Lenses

The design philosophy that went into the creation of the FA 77mm and its siblings is different from the usual wisdom applied when creating lenses. Instead of working with given focal lengths, specific apertures, and stringent requirements regarding resolution, the designer was given more leeway with the lenses' specifications. This results in odd focal lengths (31 instead of 30, 43 instead of 50, 77 instead of 85) and unusual maximum apertures. Thanks to this shift in paradigm, FA Limited lenses are able to reach an astounding level of aberration correction (at the time of launch, at least), and offer unique rendering.

In particular, eschewing the general trend towards lenses that "test well", the designer accepted some degree of field curvature (resulting in decreased resolution in the corners) and used unorthodox focal lengths (allowing a better optimization of other design parameters). The gains can be hard to quantify numerically but are tangible when looking at images. For instance, some field curvature allows for the removal of the astigmatic difference. The focal points for various colors are adjusted and aligned, and even the out-of-focus boundaries are finely tuned. These two elements, in particular, explain the so-called 3D rendering of the Limited lenses. It is a deliberate choice.

These design choices should result in lenses that are well adapted to portraiture and subject isolation. At smaller apertures, the field curvature effect becomes negligible since the depth of field increases, and the resolution figures improve across the frame.

Our reviews will evaluate to what extent this design approach worked with the three FA Limited lenses.


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