Sky-Watcher Esprit 150EDX Field Flattener

Product Overview

The Esprit 150EDX Flattener is Sky-Watcher's dedicated field corrector for the Esprit 150EDX super apochromatic refractor. The objective brings light to focus on a slightly curved surface while a camera sensor is flat, and that difference is what turns corner stars into short radial streaks while the centre of the frame is pinpoint. This corrector sits in the imaging train and flattens the focal surface onto the sensor plane.

Sky-Watcher publishes a 44 mm corrected image circle for it. A full-frame sensor measures 43.3 mm across the diagonal, so the corrected field encloses full-frame and leaves an APS-C sensor comfortably inside it.

This part flattens; it does not reduce. Sky-Watcher publishes no reduction factor, no altered focal length and no altered focal ratio for it, so the Esprit 150EDX images at its native figures with this corrector in place. The 0.77x Reducer/Flattener for the Esprit 150 (S20215) is a separate optic built for the opposite job.

Who It's For

This is the corrector Sky-Watcher pairs with the Esprit 150EDX, so it is the right part if you own that telescope and want flat, round stars across a large sensor at the scope's native focal length & ratio.

The Esprit 150 is the longest tube in the line, and the reason to flatten rather than reduce is image scale: galaxy detail, globular cluster cores, planetary nebulae and small emission knots all benefit from keeping every millimetre of native focal length. If a wider, faster field is what you are after instead, the 0.77x reducer/flattener for the Esprit 150 is the part built for that.

Key Features & Design

• Matched to the Esprit 150EDX: Sky-Watcher publishes compatibility with the Esprit 150EDX specifically, so the correction is figured for that objective rather than sold as a universal flattener.
• 44 mm corrected image circle: covers a full-frame sensor's 43.3 mm diagonal and places APS-C well inside the corrected zone.
• Flattening only: with no published reduction factor, the telescope's native focal length and focal ratio carry straight through.
• Single optic in the train: one corrector between focuser and camera, with no separate elements to align against each other.

Optical / Mechanical Design

What it corrects: field curvature across the Esprit 150EDX imaging field. The symptom it removes is radial elongation of stars toward the frame corners while the centre focuses cleanly.

Corrected image circle: 44 mm, as published by Sky-Watcher. Sensor coverage follows from that figure — full-frame spans 43.3 mm corner to corner and APS-C roughly 28 mm, so both fall inside the corrected field.

Resulting focal length and focal ratio: Sky-Watcher publishes neither, which is consistent with a flattener that works at native focal length. Only published figures appear here, so no altered numbers are given.

Required backfocus and thread interface: the vendor product page carries no backfocus distance in millimetres and no thread size, and links no manual or datasheet. Those two figures set how the corrector spaces to the sensor, so send us your camera, filter drawer or wheel and any adapters and we will work the spacing out with you.

Recommended Uses

• Deep-sky astrophotography at native focal length: galaxies, globular clusters, planetary nebulae and compact nebular detail, where the Esprit 150's image scale is the point.
• Large-sensor imaging: the 44 mm circle supports full-frame and APS-C cameras, including cooled astronomical CMOS bodies in those formats.
• Mosaics: flat corners let adjacent panels stitch without a ring of distorted stars at each seam.
• Narrowband and broadband: field curvature is geometric, so the correction holds whatever filter is in front of the sensor.

Compatibility and Accessory Notes

Sky-Watcher lists one compatible telescope for this corrector: the Esprit 150EDX. The earlier Esprit 150ED and the other tubes in the range have their own correctors, and refractors from other makers pair with theirs. Send us the exact model printed on your tube and we will confirm which corrector belongs on it.

Because the thread interface and sensor spacing are not published, the adapter stack between this corrector and your camera cannot be specified from vendor data alone. Tell us your camera model, filter wheel or drawer, and any off-axis guider, and we will map the imaging train and tell you exactly what sits where.

On the mount side nothing changes: this adds a short optic and roughly a pound behind the focuser rather than altering how the telescope rides.

Good to Know Before You Order

• Backfocus is not published. Sky-Watcher gives no spacing figure in millimetres for this corrector. Corner star shape depends on hitting the correct sensor distance, and we can work that out with you from your camera and adapters.
• Thread interface is not published. No thread size appears on the vendor page, so the camera-side connection is confirmed case by case.
• Published for the Esprit 150EDX. The 44 mm figure is stated for that telescope and is not carried across to other models.
• It is a flattener, not a reducer. Focal length and focal ratio stay at the telescope's native values; the separate 0.77x reducer/flattener is the part that changes them.
• Weight figure is the vendor's shipping weight. Sky-Watcher lists 1.0 lb for this item and publishes no separate optic-only mass in a specification table.
• Vendor image note. Sky-Watcher states "Images subject to change" on this listing, which is usual for a recently released part.

Frequently Asked Questions

Is it difficult to set up?

It is one optic that installs between the focuser and the camera and then stays there. The element that takes attention is the spacing to the sensor, which Sky-Watcher does not publish for this corrector. Send us the camera and adapters you plan to use and we will lay the train out for you.

Does it change the focal length or focal ratio?

Sky-Watcher publishes no reduction factor, resulting focal length or resulting focal ratio for it. It flattens the field at the telescope's native figures. The 0.77x Reducer/Flattener is the part that shortens focal length and speeds the ratio.

Will it cover my full-frame camera?

The published corrected image circle is 44 mm and a full-frame sensor measures 43.3 mm on the diagonal, so the sensor sits inside the corrected field. APS-C sits well inside it.

Does it fit the Esprit 150ED rather than the 150EDX?

Sky-Watcher publishes compatibility only with the Esprit 150EDX for this part. The Esprit 150ED has its own correctors in the range, including a 0.77x reducer/flattener. Send us the model on your tube and we will match it.

How much does it add to the imaging train?

Sky-Watcher lists 1.0 lb for this item — a small addition behind the focuser alongside the camera, filters and any guider.

Bottom Line

The dedicated flattener for the Esprit 150EDX, with a published 44 mm corrected circle that keeps stars round across a full-frame sensor at the telescope's native focal length. Sky-Watcher leaves backfocus and thread figures unpublished, so we confirm the spacing against your own camera and adapters and send it out ready to drop into the train.