Acutar 300mm f/6.3

Overview

The Acutar 300mm f/6.3 is a four-element Tessar-type large-format lens manufactured by Ilex Optical Co. of Rochester, New York. The Acutar series spans seven focal lengths from 165mm to 508mm, all sharing the same f/6.3 maximum aperture and the same general optical design — a Tessar derivative with a somewhat wider angle of coverage than the traditional Tessar formula, comparable in concept to Kodak's Commercial Ektar series. Calumet sold these same lenses rebadged under their Caltar name; Acutar and Caltar specimens are interchangeable.

The 300mm is the longest Acutar focal length still useful as a "normal" lens — comfortable on 5×7 and just covering 8×10. Its 325mm image circle clears the 8×10 effective diagonal (~310mm) with ~15mm of headroom, enough for very small rise or fall but not generous swings or tilts. On 5×7 it's well-corrected with generous movement room (~115mm spare). On 4×5 it functions as a long lens (roughly twice the 4×5 diagonal). The lens mounts in a Copal 1 shutter.

Optical design

Four elements in three groups, Tessar derivative. The somewhat wider angle of coverage versus a classical Tessar makes the lens better-matched to LF cameras that exploit movements; on 8×10 specifically, the modest movement headroom is the practical limit, not optical correction. Performance is at its best at typical large-format working apertures (f/16–f/32).

Format coverage

Format	Covers?	Movement headroom
4×5	yes	very generous — long-lens use
5×7	yes	generous (~115mm spare)
8×10	yes	minimal (~15mm — careful with movements)

Related lenses

• Acutar 165mm f/6.3 — shortest Acutar; 4×5 only
• Acutar 210mm f/6.3 — most popular Acutar; comfortable 4×5 normal