Sky-Watcher Field Flattener 1.25″ for EvoGuide 50
The Sky-Watcher field flattener (1.25″) designed for the Sky-Watcher EvoGuide 50ED and other ultra-short focal length APO refractors solves one of the most common problems in astrophotography with compact guide telescopes. Short focal length refractors inherently produce significant field curvature. Stars look perfectly round at the centre of the image, but towards the corners they start to stretch into characteristic elongated shapes. When using a guiding camera, this directly affects guiding accuracy and the overall quality of your shots. This field flattener corrects field curvature effectively, delivering sharp, point-like stars across the entire sensor.
27mm field coverage - no compromises for APS-C
The 27mm field coverage handles the APS-C format without compromise. You can use this flattener not only with guiding cameras but also for imaging with larger sensor cameras. M42 thread camera connection ensures compatibility with a wide range of cameras and adapters commonly available in the astrophotography market. The compact 51mm diameter places no restrictions on the light path, and the flattener integrates cleanly into the optical train without any additional modifications.
Key specifications
| Parameter |
Value |
| Type |
Field flattener |
| Barrel diameter |
1.25″ |
| Field coverage |
27mm |
| Camera connection |
M42 thread |
| Outer diameter |
51mm |
| Compatible telescope |
Sky-Watcher EvoGuide 50ED and similar short focal length APO refractors |
Who is this field flattener for?
This accessory is the right choice if you:
- use the Sky-Watcher EvoGuide 50ED or a similar compact APO refractor for astrophotography
- notice stretched or elongated stars in the corners of your images
- want to improve guiding accuracy with your guiding camera
- shoot on an APS-C sensor and need full, sharp coverage across the frame
- prefer a simple, tool-free integration into your existing optical train
Why field curvature matters in astrophotography
A short focal length is a great advantage for wide-field imaging and guiding. However, it comes with a trade-off - field curvature. Without correction, only the centre of the image stays sharp. Stars near the edges and corners appear elongated, which reduces the quality of the final image and makes guiding less reliable. A field flattener corrects this optical distortion and gives you consistently sharp stars from edge to edge. This is especially important when you are using a guiding camera, where accurate star shapes are essential for precise autoguiding.
