Field Performance
The Askar FRA400 (Flatfield Refractive Astrograph) is designed to solve the biggest headache in wide-field astrophotography: backfocus. Thanks to its quintuplet design, the field flattener is built directly into the tube, meaning you don't have to worry about the precise distance between the sensor and the glass.
Optically, it features a 72mm aperture with two ED (Extra-low Dispersion) glass elements. In my testing across targets like the North American Nebula, the color correction was superb. When paired with the dedicated 0.7x Reducer, it transforms into a fast 280mm f/3.9 system, making it an incredibly versatile wide-field instrument for full-frame sensors.
Strengths
- Native flat field (No backfocus math)
- Full-frame 44mm image circle
- Fast f/3.9 speed with reducer
- Heavy-duty 3" Rack & Pinion Focuser
Considerations
- Dovetail is short for balanced mono rigs
- Requires tools for tube ring adjustments
- Noticeable weight for its small size