Sky-Watcher Esprit 150 EDX Super APO Triplet f/7 Telescope

The Esprit 150EDX: A 150 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.

Optical Design: An Air-Spaced Triplet with Ohara FPL-53 ED Glass

The three-element, air-spaced objective includes one Ohara FPL-53 ED element. The Esprit 150 manual says false color is extremely well corrected, with no 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: Over 170 mm of Back Focus

With the 2-inch adapter installed, the manual gives more than 170 mm of visual back focus from the end of the focuser tube.

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.

The Optional Field Flattener: 44 mm, 100 mm Back Focus

The optional Esprit 150 full-frame field flattener is sold separately. It gives excellent field flatness and full illumination across the 44 mm imaging plane, and it is not compatible with other telescopes.

Remove the 2-inch ring adaptor before installing the flattener. The flattener needs exactly 100 mm from its last lenses to the sensor; with a DSLR, the drawtube adaptor, flattener, extender tube and an enlarged 48mm T-ring for your camera give that distance.

• Astronomy camera: a custom ring with a female M62x1 thread for the flattener exit, a thread for the first part of your optical train, and a length that puts the sensor exactly 100 mm from the flattener's last lenses.
• Reducer: skywatcher.com lists an optional 0.77x reducer/flattener; the manual covers only the field flattener.

Focuser System: The 3-inch Dual-Speed, Rotatable, and Indexed 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.

• Dual-speed 11:1 focus: turn the knobs until the image is nearly sharp, then use the 1:11 knob.
• Rotatable body: an improved back end without the previous model's capstan wheel makes the focuser body easier to rotate. Remove all accessories, fully retract the drawtube, loosen the screw, rotate the body and lock the screw.
• 360° rotatable adaptor: on the drawtube, to help frame your images.
• Indexed drawtube: the scale shows the focus position for each accessory, followed by fine tuning.
• Drawtube Thread: The focuser terminates in a male M74 x 1 thread for a solid connection to the optional flattener and other accessories.

Mechanical Construction: A 15.2 kg OTA with CNC-Machined Components

The optical tube weighs 15.2 kg (33.5 lb) and measures 920 mm with the dew shield retracted. It comes with CNC-machined aluminum tube rings with an accessory rail that doubles as a carrying handle, and a 75 mm D-style (Losmandy) dovetail bar.

Extended, the dew shield brings the length to 1030 mm: loosen the two screws on its aluminum ring, pull it forward and tighten them again. A camera adapter and a foam-lined aluminum case are included.

Imaging Train Integration: M74, M62, and 48 mm Connections

The main drawtube terminates in an M74 x 1 male thread, which is the primary attachment point for the optional field flattener assembly.

When using the flattener with a DSLR, the extender tube takes an enlarged 48mm T-ring for your camera. For filter users, this extender tube contains an internal 48 x 0.75 mm thread in its closing ring, for a 2-inch filter; do not overtighten it. The manual suggests a light pollution reducer filter for suburban skies. For connecting a dedicated astronomy camera, a custom adapter must be made to connect to the flattener's M62x1 female thread.

Mounting the 15.2 kg Optical Tube

The optical tube weighs 15.2 kg (33.5 lb) 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 tube plus your camera, guider and accessories.

Cool-Down and Solar Safety

The manual says the telescope needs at least 30 minutes to cool to outside conditions, and longer with a big temperature difference, to avoid tube currents.

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.

First Night Setup: A Step-by-Step Guide for the Esprit 150EDX

A first night, in order:

1. Cool-down: allow at least 30 minutes for the telescope to reach outside temperature.
2. Mounting: Securely attach the D-style dovetail bar to your mount's saddle plate. Attach your camera, diagonal, and other accessories before balancing.
3. Balancing: with all accessories attached, balance the telescope on both axes.
4. Initial Focusing: If imaging, remove the 2-inch adapter and install the flattener and camera. Unlock the focuser's locking lever, turn the knobs until the image is nearly sharp, then use the 1:11 knob.
5. Framing: Use the 360° rotatable adaptor on the drawtube to frame your target. Lock the focuser drawtube if you have a heavy imaging train attached.