Sky-Watcher Esprit 120 EDX Super APO Triplet f/7 Telescope

The Esprit 120EDX: A 120 mm f/7 Triplet Refractor

Sky-Watcher designs the Esprit EDX series primarily for astro-imagers, and says they are also fine telescopes for visual observation. The 120EDX keeps the f/7 optical system of the previous model.

An f/7 Air-Spaced Triplet with Ohara FPL-53 Glass

The objective is a three-element, air-spaced apochromatic triplet with one Ohara FPL-53 ED element. The Esprit 120 manual says false color is extremely well corrected and describes no visual color fringing even on bright objects.

The optical system is knife-edge baffled, and each air-to-glass lens surface carries Sky-Watcher's Metallic High-Transmission Coatings (MHTC).

Visual Use: 170 mm of Back Focus

With the 2-inch adapter installed, accessories needing 170 mm of back focus or less from the end of the focuser tube can be used. The drawtube adaptor accepts a 2-inch star diagonal, and loosening a screw lets the diagonal ring rotate.

Sky-Watcher supplies the telescope without eyepiece, star diagonal and finderscope. The finderscope mounting shoe takes Sky-Watcher finderscopes, and the finder can be removed during observation if it obstructs your view.

Optional Field Flattener and 0.77x Reducer/Flattener

Two optically matched correctors are sold separately. Neither is compatible with other telescopes, even refractors of the same aperture and focal length. Remove the 2-inch ring adaptor from the drawtube before fitting either.

• Field flattener: a flat, fully illuminated 44 mm imaging plane at 75 mm back focus.
• 0.77x reducer/flattener: full frame, with a 34 mm imaging plane and 95 mm back focus. It screws directly onto the focuser drawtube.

The 3-inch Dual-Speed 11:1 Rack and Pinion Focuser

The 3-inch CNC-machined rack and pinion linear power focuser has dual-speed 11:1 fine focusing; it offers a high accessory load capacity and zero image shift. A locking lever below the focuser holds it when a heavy load is attached.

The indexed scale on the drawtube shows the focus position for each accessory, followed by fine tuning. An improved back end without the previous model's capstan wheel makes the whole focuser body easier to rotate: remove all accessories, fully retract the drawtube, loosen the screw, rotate the body and lock the screw. The 360° rotatable adaptor on the drawtube helps frame images.

A 10.84 kg OTA with D-Style Bar and Case

The optical tube assembly weighs 10.84 kg (23.9 lb) and measures 710 mm long with its dew shield retracted, 810 mm extended. To extend the dew shield, you loosen the two screws on its aluminum ring, pull it forward, and retighten them.

It comes with CNC-machined aluminum tube rings with an accessory rail that doubles as a carrying handle, a 75 mm D-style (Losmandy) dovetail bar, a camera adapter and a foam-lined aluminum case.

M74, M48, and Custom Adapter Connections

The focuser drawtube terminates in a male M74 x 1 thread, which is the primary connection point for the optional correctors.

• DSLR Connection: Screw on the corrector, then the extender tube and an enlarged M48 x 0.75 T-ring (sold separately) that matches your camera.
• Astronomy Camera Connection: A custom ring is machined, with a female M62x1 thread for the flattener and a length that gives the 75 mm back focus.
• Filter Integration: A 48mm (2") filter threads into the closing ring of the DSLR extender tube; do not overtighten it. The manual suggests a light pollution reducer filter for suburban skies.

Mounting the 10.84 kg Optical Tube

The optical tube weighs 10.84 kg (23.9 lb) before a camera or other accessories, and mounts with a 75 mm D-style (Losmandy) dovetail bar. Choose a mount with a D-style saddle and a payload rating that covers the whole imaging rig.

Cool-Down and Solar Safety

The manual says the telescope needs at least 25 minutes to cool to outside conditions, to avoid tube currents. If there is a large temperature difference between your storage area and the outdoors, allow for a longer acclimation time.

Never look directly at the Sun through the telescope: permanent eye damage will result. Use a proper solar filter firmly mounted on the front, never an eyepiece-type solar filter, and never project sunlight onto another surface. Cap or remove the finderscope when observing the Sun, and never leave a telescope pointing at the Sun unattended.

A 4-Step DSLR Imaging Setup

The manual's four steps for a DSLR with the optional field flattener give the 75 mm back focus:

1. Attach Drawtube Adapter: First, screw the drawtube adapter onto the M74 x 1 male thread at the end of the focuser tube.
2. Install Field Flattener: Screw the dedicated field flattener onto the drawtube adapter.
3. Add Extender Tube: Screw the extender tube onto the rear thread of the field flattener.
4. Connect Camera: Finally, screw the appropriate enlarged M48 T-ring (sold separately) for your camera model onto the extender tube, and then attach your DSLR.

Once assembled, you can use the focuser's indexed scale to find the approximate focus point, then use the 11:1 fine-focus knob to achieve a sharp image. The optional 0.77x reducer screws directly onto the drawtube and needs 95 mm of back focus.