Sharper off-axis stars
Correction is concentrated where a flat camera sensor needs it most: away from the centre, where native field curvature is increasingly visible.
Sky-Watcher 0.92x Reducer/ Flattener for Esprit 100EDX
Authorised Dealer
Sky-Watcher · Esprit EDX imaging
Make the whole frame count.Esprit 100EDX field flattener
Built around the Esprit 100EDX optical path, SWA-ESPR100FF corrects the telescope's naturally curved focal surface so off-axis stars meet a flat camera sensor with far better control. It keeps the native 550 mm focal length and f/5.5 focal ratio intact.
1.0×Field flattening without focal reduction
550 mmEsprit 100EDX native focal length retained
f/5.5Native focal ratio retained for imaging
63 mmTotal specified distance to the sensor
40 mmPublished fully illuminated field
44 mmNominal corrected field for the EDX system
Field curvature · corrected
Correct the field. Keep the focal length.
A refractor can focus the centre and outer field onto slightly different surfaces. A flat sensor cannot follow that curve, so edge stars may stretch even when the centre is sharply focused. The matched flattener reshapes the converging light so more of the frame reaches one flat focal plane.
Native framing retained
The field flattener does not act as a focal reducer. Image scale, framing and exposure behaviour remain those of the 550 mm f/5.5 Esprit 100EDX.
Matched, not universal
The correction is designed around the 100 mm Esprit optical prescription and its spacing. Matching the corrector to the tube matters.
Important: this accessory is a field flattener. It may sit inside a retailer category labelled “reducers and flatteners”, but SWA-ESPR100FF does not reduce the Esprit 100EDX focal length.
Sensor coverage · made visible
Know what 40 mm and 44 mm describe.
Published specifications separate illumination from correction. The 100EDX system is associated with a nominal 44 mm corrected field, while Sky-Watcher's corrector specification gives a 40 mm fully illuminated field. That distinction matters most at the corners of a 43.3 mm-diagonal full-frame sensor.
Corrected field
Large enough in nominal diameter to address the 43.3 mm diagonal of a 36 × 24 mm sensor. Corner performance still depends on exact spacing, tilt and the complete optical train.
Illuminated field
The fully illuminated region is smaller than a full-frame diagonal. Full-frame users should expect to capture flats and preserve a clear, generously sized adapter path.
Comfortably inside
A typical APS-C diagonal sits well inside the published illuminated field, giving the corrector more room around the sensor boundary.
Back focus · 63 millimetres
Measure from the right surface.
Back focus is an optical requirement, not simply the amount of focuser travel available. The sensor must sit 63 mm behind the flattener's published M66 reference shoulder. With the standard 8 mm M48 adapter fitted, the remaining camera train is built to 55 mm.
63 mm from the M66 shoulder
This is the complete optical distance from the flattener's camera-side reference to the sensor. Count every adapter, spacer, filter drawer, wheel, off-axis guider and the camera's own flange-to-sensor depth.
55 mm after the 8 mm adapter
With the standard M48 adapter left in place, the familiar 55 mm camera-train target remains. This is why many astronomy cameras can be configured with their supplied spacer sets.
Filters change optical distance
A practical starting allowance is approximately one-third of the filter glass thickness. A 2 mm filter may therefore need roughly 0.7 mm of additional mechanical spacing.
Tune after the mechanical build
Published spacing is the starting point. Test all four corners on a well-focused star field and adjust with thin rings only after checking tilt, thread seating and flexure.
Purpose-matched compatibility
Designed around the Esprit 100EDX.
The corrector is selected by telescope model, not simply by focuser diameter. Its lens prescription, threaded fit and working distance are matched to the 100 mm Esprit system. Do not substitute the 70, 80, 120 or 150 mm Esprit corrector.
Primary match
Sky-Watcher Esprit 100EDX 100 mm f/5.5 triplet refractor.
Regional legacy listing
SWA-ESPR100FF is also listed by Australasian distributors for the original Esprit 100ED. Confirm the exact tube and thread if fitting a pre-EDX model.
Not universal
Not the matching corrector for Esprit 70EDX, 80EDX, 120EDX, 150EDX or other refractor families.
Thread · space · test
Build a rigid path to the sensor.
Good corner stars depend on optical correction and mechanical discipline. Keep the path threaded, square and correctly spaced from the focuser to the sensor.
1
Expose the imaging thread
Remove the visual accessory holder or adapter specified by the telescope instructions. Keep every mating surface clean and free from grit.
2
Thread the flattener squarely
Start the thread by hand and stop if resistance appears early. A cross-threaded or incompletely seated corrector can introduce tilt before imaging begins.
3
Build the 63 mm distance
Add the physical depth of every component to the camera sensor. With the fitted 8 mm M48 adapter, target 55 mm behind its rear reference face.
4
Focus, inspect and refine
Focus near the centre, inspect all four corners at full scale and use small spacer changes only when the pattern is consistent across the frame.
Read the frame before changing spacing
All four corners change similarly
Back-focus spacing is a likely variable. Test one small change at a time and keep the centre focus consistent.
One side or one corner is worse
Check sensor tilt, adapter seating, focuser sag and cable load before treating the issue as a simple spacing error.
The whole frame is soft
Verify focus, seeing, tracking, dew and objective temperature before diagnosing field correction.
Optical and mechanical purpose
One accessory. Three jobs in the imaging train.
The flattener is both an optical corrector and a structural part of the camera train. Its value comes from matching the Esprit prescription, preserving the native focal geometry and replacing a loose push-fit path with threaded interfaces.
Flattens the focal surface
Moves off-axis focus toward the same plane as the centre so a flat digital sensor can record more consistent star shapes across the image.
Preserves native scale
No focal reduction means the Esprit 100EDX remains a 550 mm f/5.5 system. Existing framing and image-scale calculations stay valid.
Supports a threaded train
The dedicated M65/M66 body and M48 adapter give the camera train a positive mechanical path that is better suited to repeatable imaging than a simple slip fit.
Package and supporting parts
Core package
- Sky-Watcher field flattener for Esprit 100EDX
- Standard 8 mm M48 imaging adapter configuration
- Protective caps for storage and transport
Imaging system parts are separate
- Esprit 100EDX telescope and mount
- Camera-specific T-ring or threaded adapter
- Spacers, filter hardware, off-axis guider and camera
Comprehensive specifications
Sky-Watcher SWA-ESPR100FF.
Specifications are separated into optical behaviour, interfaces and system fit so the corrector can be checked against a real camera train before assembly.
Optical performance
- Accessory type
- Dedicated field flattener / field corrector
- Optical factor
- 1.0× — no focal-length reduction
- 100EDX focal length
- 550 mm retained
- 100EDX focal ratio
- f/5.5 retained
- Primary correction
- Field curvature and associated off-axis star deformation
- Corrected field
- 44 mm nominal EDX corrected field
- Illuminated field
- 40 mm published corrector field
- Intended use
- Prime-focus deep-sky astrophotography
Interfaces and spacing
- Product code
- SWA-ESPR100FF
- Attachment
- Thread-on optical corrector
- Telescope side
- M65×1 female thread
- Corrector output
- M66×1 male thread
- Imaging adapter
- M48×0.75 interface, 8 mm standard adapter length
- Total back focus
- 63 mm from the published M66 reference shoulder to sensor
- After M48 adapter
- 55 mm from adapter reference face to sensor
- Adjustment method
- Fixed optics; spacing is tuned with threaded rings in the camera train
Compatibility
- Primary telescope
- Sky-Watcher Esprit 100EDX
- Native telescope
- 100 mm aperture, 550 mm focal length, f/5.5 triplet APO
- Regional listing
- Also listed for the original Esprit 100ED; confirm pre-EDX tube interface before purchase
- Sensor formats
- APS-C comfortably within the illuminated field; full frame uses the outer corrected field and benefits from flat calibration
- Other Esprit sizes
- Use the model-specific corrector; not a universal 70/80/120/150 mm Esprit accessory
System requirements
- Camera connection
- Appropriate M48 T-ring or threaded astronomy-camera adapter
- Spacing hardware
- Selected to total 63 mm, including camera flange depth and all accessories
- Filters
- Include the optical effect of filter glass when fine-tuning spacing
- Calibration
- Dark, bias/dark-flat and flat-field frames according to the camera workflow
- Not included
- Telescope, camera, T-ring, filter system, off-axis guider and model-specific spacers
Specification note: Sky-Watcher regional material distinguishes a 44 mm corrected EDX field from a 40 mm illuminated corrector field. Full-frame corner illumination therefore depends on the complete imaging train and should be calibrated with flats. Manufacturer specifications and package presentation can change without notice.
Before first light
Protect the glass. Validate the train.
Small habits preserve optical performance and make troubleshooting faster when the first clear night arrives.
Keep the supplied caps fitted whenever the corrector is off the telescope. Store it dry and protected from loose metal parts.
Remove loose dust with a blower before using approved optical cleaning materials. Avoid touching the lens surfaces.
Note each component's mechanical depth and photograph the working train so a successful configuration can be rebuilt.
Flats correct illumination fall-off and dust shadows from the assembled train; capture them without changing focus or camera orientation.
Jacobs Digital is a speciality on-line retailer, as well as a brick-and-mortar retail store, operating in the same Auckland, NZ location for over 40 years.
9 Mokoia Road
Birkenhead
Auckland 0626
New Zealand
+64 (9) 480-5903
