telescopecomparison · 2-way
William Optics RedCat 91 vs Askar FRA500
William Optics
RedCat 91
Best suited for beginners and wide-field enthusiasts running a portable travel rig.
Specifications
| Specification | William Optics RedCat 91 | Askar FRA500 |
|---|---|---|
| Optics | ||
| Type | Refractor | Refractor |
| Optical design | Petzval APO | Petzval Quintuplet APO |
| Aperture | 91mm | 90mm |
| Focal length | 496mm | 500mm |
| Native f/ratio | f/5.5 | f/5.6 |
| Image circle | 45mm | 60mm |
| Full-frame support | Yes | Yes |
| Physical | ||
| Weight | 4.3kg | 5.4kg |
Advantages of William Optics RedCat 91
- Lighter (4.3kg vs 5.4kg) — easier to travel with
Advantages of Askar FRA500
- Larger image circle (60mm) — supports bigger sensors
Best for — William Optics RedCat 91
- Large emission nebulae and star clusters
- Full-frame astro cameras and DSLRs
Best for — Askar FRA500
- Large emission nebulae and star clusters
- Full-frame astro cameras and DSLRs
William Optics RedCat 91 — typical FOV & scale
- With Full-frame (36×24mm, 3.76µm)FOV: 4.16° × 2.77°Scale: 1.56"/px
- With APS-C (23.5×15.7mm, 3.76µm)FOV: 2.71° × 1.81°Scale: 1.56"/px
- With IMX533 square (11.3×11.3mm, 3.76µm)FOV: 1.31° × 1.31°Scale: 1.56"/px
Askar FRA500 — 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 — recommended user
Best suited for beginners and wide-field enthusiasts running a portable travel rig.
Askar FRA500 — recommended user
Best suited for beginners and wide-field enthusiasts running a backyard imaging setup.