Pentax SF-X1987

History

Minolta's Maxxum 7000 (1985) and Canon's EOS 650 (1987) had both entered the autofocus SLR market before Pentax. The SF-X arrived in 1987 and carried a significant design decision: rather than developing an entirely new lens mount (as Minolta had with the A-mount and Canon with EF), Pentax extended its existing K-mount with autofocus contacts. This KAF mount preserved backward compatibility with the entire installed base of K and KA manual-focus lenses, accepting them in manual-focus operation with full metering. The trade-off was AF speed and accuracy constrained by motor placement; early KAF AF lenses used a body-driven screwdriver coupling, requiring the lens to carry its own helicoid.

The SF-X was released simultaneously with the first KAF autofocus lenses: the FA 35-70mm f/3.5-4.5 and FA 70-210mm f/4-5.6 zooms. The built-in pop-up flash - covering approximately GN 12 at ISO 100 - was immediately influential; Canon, Nikon, and Minolta all introduced built-in flash on consumer SLRs within two years. Pentax updated the body to the SF7 (a cosmetically differentiated variant) before moving to the more capable PZ-1 in 1991.

Why It Matters

Two claims attach to the SF-X reliably. First, it is Pentax's first commercially sold autofocus SLR, making it the entry point for the KAF system that would carry Pentax through the 1990s and into DSLR production. Second, it is the first SLR with a built-in pop-up flash - a feature so convenient it became a default on virtually every consumer SLR and DSLR made afterward.

The AF performance, judged against 2026 standards, is slow: single-point, body-driven screwdriver coupling, no predictive tracking. Contemporary reviews noted it was noticeably behind Canon EOS in autofocus speed. For static subjects and moderate action it was adequate; for sports and fast movement it required anticipation. This limitation did not prevent the SF-X from succeeding in the consumer market, where the combination of built-in flash, PASM, and K-mount backward compatibility was compelling.

For current buyers, the SF-X is primarily of interest as an entry into the Pentax KAF lens ecosystem - particularly the FA-series primes (FA 50/1.4, FA 77/1.8 Limited, FA 31/1.8 Limited) and the extensive K/M/A manual-focus back-catalog. The 1/100s flash sync is lower than ideal, and the single 2CR5 battery is expensive relative to common AA alternatives on competing bodies.

Lenses & Accessories

Pentax KAF mount. Autofocus operates with KAF and KAF2 lenses; older KA, K, and M lenses mount and meter in manual focus. The full FA prime lineup works with matrix metering and TTL flash on this body. SMC Pentax-A lenses work in aperture-priority and manual modes. Notable glass for this system: FA 50mm f/1.4, FA 28mm f/2.8, FA 85mm f/1.8, FA 35-80mm f/4-5.6 (kit zoom), FA 70-210mm f/4-5.6. Motor drive: the Body Motor Grip F adds a power winder. TTL flash: AF280T, AF360FGZ (check compatibility); the built-in flash covers guide number ~12 (ISO 100 meters).

Sample Photographers / Notable Use

• Volume consumer and semi-enthusiast body; not specifically associated with named photographers in published record.
• Historically significant as Pentax's AF launch platform; reviewed in all major photography magazines of the era (Popular Photography, Modern Photography, Camera & Darkroom).
• Frequently cited in Pentax history as the camera that kept the K-mount system relevant through the autofocus transition.

References

• Camera-Wiki: Pentax SF-X - specifications and marketing variant names
• Wikipedia: Pentax SF1 - covers SF-X / SF1 / SFX-N as a single entry
• Pentax Forums: Pentax SF-X - user reports and real-world AF performance notes