Esprit 120ED Pro — 120/840 triplet apochromat The original Esprit 120ED Pro is an air-spaced triplet apochromat with 120 mm aperture, 840 mm focal length and f/7 focal ratio. It is designed for imaging and visual astronomy, with fully multi-coated optics and a mechanically supported imaging train.
Manufacturer model: Esprit 120ED Pro — 120/840 triplet apochromat · Specifications checked against manufacturer data on 2026-11-04
The original Esprit 120ED Pro is an air-spaced triplet apochromat with 120 mm aperture, 840 mm focal length and f/7 focal ratio. It is designed for imaging and visual astronomy, with fully multi-coated optics and a mechanically supported imaging train.
The original two-element thread-on flattener produces a manufacturer-specified 44 mm illuminated corrected field. Its sensor spacing is 75 mm measured from the rear flat surface of that flattener. This is not the spacing measured from the M48 end of an attached extension, and it does not apply to a different reducer or EDX corrector.
The global product page identifies a 3-inch linear-power focuser. The manual shows an M74 × 1 focuser output, an M65 × 1 flattener input and a M62 × 1 male flattener output; the DSLR extension terminates in M48 × 0.75. Use the matching original adapters when assembling the camera train.
The manual documents a 9×50 right-angle erect-image finder, 2-inch dielectric diagonal and tube rings with a 3-inch D-style dovetail. Its technical table lists 10 kg OTA mass and 762 mm length. These manual values are used consistently rather than mixing regional accessory packages.
Sky-Watcher manufacturer documentation
Sky-Watcher original product page
Original Esprit manual configuration used. The global web table differs in finder magnification, OTA mass/length and practical power; the explicit manual values are used, with the global page only supplying focuser size. Legacy manual threads/backfocus are not assigned to EDX models.
| Field flattener | Matched thread-on two-element field flattener |
|---|---|
| Corrected illuminated field (mm) | 44 |
| Flattener backfocus (mm) | 75 |
| Flattener backfocus reference | From the rear flat surface of the specified original flattener to sensor |
| Visual backfocus | Greater than 225 mm from the focuser end with 2-inch adapter |
| Resolution rayleigh (arcsec) | 1.16 |
| Resolution dawes (arcsec) | 0.97 |
| Lowest useful magnification | 17 |
| Highest useful magnification | 283 |
| Focuser output thread | M74 × 1 male |
| Drawtube adapter threads | M74 × 1 female to M65 × 1 male |
| Flattener input thread | M65 × 1 female |
| Flattener output thread | M62 × 1 male |
| Dslr extension output thread | M48 × 0.75 male |
Data sheet
Esprit 120ED Pro — 120/840 triplet apochromat The original Esprit 120ED Pro is an air-spaced triplet apochromat with 120 mm aperture, 840 mm focal length and f/7 focal ratio. It is designed for imaging and visual astronomy, with fully multi-coated optics and a mechanically supported imaging train.
Manufacturer model: Esprit 120ED Pro — 120/840 triplet apochromat · Specifications checked against manufacturer data on 2026-11-04
