telescopecomparison · 2-way
William Optics RedCat 91 WIFD vs Borg 90FL
William Optics
RedCat 91 WIFD
Best suited for beginners and wide-field enthusiasts running a portable travel rig.
Key differences
-10% focal length
Faster by 0.7 f-stops
Specifications
| Specification | William Optics RedCat 91 WIFD | Borg 90FL |
|---|---|---|
| Optics | ||
| Type | refractor | refractor |
| Optical design | Petzval (5-element advanced) | Apo doublet fluorite |
| Aperture | 91mm | 90mm |
| Focal length | 448mm | 500mm |
| Native f/ratio | f/4.9 | f/5.6 |
| Image circle | 55mm | — |
| Full-frame support | Yes | No |
| Physical | ||
| Weight | 4.7kg | 2.5kg |
Advantages of William Optics RedCat 91 WIFD
- Wider field — 448mm vs 500mm focal length
- Faster optics at f/4.9 vs f/5.6
- Larger image circle (55mm) — supports bigger sensors
Advantages of Borg 90FL
- Tighter framing — 500mm vs 448mm focal length
- Lighter (2.5kg vs 4.72kg) — easier to travel with
Best for — William Optics RedCat 91 WIFD
- Large emission nebulae and star clusters
- Fast imaging — short exposures per sub
- Full-frame astro cameras and DSLRs
Best for — Borg 90FL
- Large emission nebulae and star clusters
William Optics RedCat 91 WIFD — typical FOV & scale
- With Full-frame (36×24mm, 3.76µm)FOV: 4.60° × 3.07°Scale: 1.73"/px
- With APS-C (23.5×15.7mm, 3.76µm)FOV: 3.01° × 2.01°Scale: 1.73"/px
- With IMX533 square (11.3×11.3mm, 3.76µm)FOV: 1.45° × 1.45°Scale: 1.73"/px
Borg 90FL — typical FOV & scale
- With Full-frame (36×24mm, 3.76µm)FOV: 4.13° × 2.75°Scale: 1.55"/px
- With APS-C (23.5×15.7mm, 3.76µm)FOV: 2.69° × 1.80°Scale: 1.55"/px
- With IMX533 square (11.3×11.3mm, 3.76µm)FOV: 1.29° × 1.29°Scale: 1.55"/px
William Optics RedCat 91 WIFD — recommended user
Best suited for beginners and wide-field enthusiasts running a portable travel rig.
Borg 90FL — recommended user
Best suited for beginners and wide-field enthusiasts running a portable travel rig.
