The SL66 represented a change in direction for Rollei, which until that time had focused almost exclusively on its popular twin lens reflex cameras, the Rolleiflex and Rolleicord.

However, the rapid adoption of SLRs during the 1960s meant that Rollei risked falling behind in this market at a time when demand for TLRs was decreasing.

The Rolleiflex SL66 did not feature in Rollei's worldwide product catalog in 1980, and the US importer's July 1979 dealer price list has no SL66 cameras nor 40mm, 250mm, or 500mm lenses.

Compared to the SL66, the SL66E, introduced in 1982, adds three silicon photodiodes (SPD) for center-weighted averaging metering through the lens (TTL).

Like the Rolleiflex TLR and the Hasselblad SLR, the SL66 uses 120 or 220 rollfilm to produce frames of up to 6×6 cm (nominal); the actual image size is based on imperial units, measuring 2+1⁄4×2+1⁄4 in (57×57 mm).

[4]: 26 The body is equipped with a front lens standard which extends on a bellows for focusing, controlled by a large knob which falls under the photographer's left hand while using the camera.

A depth of field preview control is provided on the front lens standard, just ahead of the magnification scale on the side of the bellows support.

[6] As standard equipment, the SL66 comes with a folding waist-level finder with a built-in magnifier and a ground glass focusing screen with a central microprism spot, grid lines etched at 11 mm (0.43 in) intervals, and an integrated Fresnel lens.