Sky-Watcher Esprit 150ED .77x Reducer Field Flattener

Sky-Watcher Esprit 150ED 0.77x Reducer/Field Flattener
Purpose-Built Wide-Field Performance for the Esprit 150ED Apochromatic Refractor

The Sky-Watcher 0.77x Reducer/Field Flattener for the Esprit 150ED is a dedicated optical accessory engineered to bring faster imaging speed, wider fields, and pinpoint star correction to one of Sky-Watcher’s flagship triplet refractors. Designed specifically for the optical profile of the Esprit 150ED, this reducer/flattener enhances deep-sky imaging by delivering crisp, flat, and wide fields without the guesswork of third-party optics.

By reducing the focal ratio from f/7 to f/5.4, this unit shortens the Esprit 150ED’s native 1050mm focal length to approximately 808mm. The result is a faster system that gathers more light per unit time, making it ideal for large nebulae, galaxies, and star fields where expansive framing and reduced exposure times are critical.

A standout feature of this reducer is its 36mm fully illuminated image circle. While not large enough to fully cover a full-frame sensor, it offers generous illumination for APS-C sensors and smaller-format cooled astronomy cameras, with only minimal vignetting toward the corners in some full-frame setups. When paired with a sensor matched to the image circle, the result is clean, flat-field images with tight, round stars across the frame—no field curvature, no corner distortion.

The reducer also serves as a field flattener, correcting the natural off-axis aberrations inherent in refractors when used for imaging. Sky-Watcher has tuned this unit to the optical signature of the Esprit 150ED, so you're not just speeding up your imaging—you’re sharpening and correcting it, too. Full multi-coatings on every optical surface enhance light transmission and contrast, while minimizing stray reflections and internal ghosting.

Installation is straightforward. The reducer has a standard M48 rear thread and provides 55mm of backfocus—perfect for use with most DSLR and dedicated astronomy camera setups using standard spacer rings or T-adapters.

Key Features:

• Custom-designed for the Sky-Watcher Esprit 150ED refractor

• 0.77x reduction: f/7 becomes f/5.4, for faster, wider imaging

• Shortens focal length from 1050mm to 808mm

• Delivers a 36mm fully illuminated image circle—ideal for APS-C sensors

• Offers limited use with full-frame sensors (some edge vignetting expected)

• Corrects field curvature for edge-to-edge sharpness

• Fully multi-coated optics for high contrast and low reflection

• Standard 55mm backfocus spacing

• Rear M48 thread for wide, compatible connections

If you're imaging with an APS-C or similarly sized sensor and want to capture wide, flat, and detailed astrophotos with your Esprit 150ED, this reducer/flattener is a must-have. It’s not just a speed booster—it’s a sharpness and framing enhancer, carefully matched to your optical system.

For astrophotographers who demand performance without compromise, this reducer is a natural extension of the Esprit 150ED’s high-end imaging pedigree.