telescopecomparison · 2-way
William Optics RedCat 71 vs William Optics FLT 91
William Optics
RedCat 71
Best suited for beginners and wide-field enthusiasts running a portable travel rig.
William Optics
FLT 91
Best suited for intermediate imagers building a versatile kit running a portable travel rig.
Key differences
-35% focal length
-22% aperture
Faster by 1.0 f-stops
Specifications
| Specification | William Optics RedCat 71 | William Optics FLT 91 |
|---|---|---|
| Optics | ||
| Type | Refractor | Refractor |
| Optical design | Petzval APO | Triplet APO |
| Aperture | 71mm | 91mm |
| Focal length | 350mm | 540mm |
| Native f/ratio | f/4.9 | f/5.9 |
| Image circle | 45mm | 44mm |
| Full-frame support | Yes | Yes |
| Physical | ||
| Weight | 2.7kg | 4.5kg |
Advantages of William Optics RedCat 71
- Wider field — 350mm vs 540mm focal length
- Faster optics at f/4.9 vs f/5.9
- Lighter (2.7kg vs 4.5kg) — easier to travel with
Advantages of William Optics FLT 91
- Tighter framing — 540mm vs 350mm focal length
- 28% more light-gathering aperture
Best for — William Optics RedCat 71
- Wide-field nebulae and Milky Way regions
- Fast imaging — short exposures per sub
- Full-frame astro cameras and DSLRs
Best for — William Optics FLT 91
- Large emission nebulae and star clusters
- Full-frame astro cameras and DSLRs
William Optics RedCat 71 — typical FOV & scale
- With Full-frame (36×24mm, 3.76µm)FOV: 5.89° × 3.93°Scale: 2.22"/px
- With APS-C (23.5×15.7mm, 3.76µm)FOV: 3.85° × 2.57°Scale: 2.22"/px
- With IMX533 square (11.3×11.3mm, 3.76µm)FOV: 1.85° × 1.85°Scale: 2.22"/px
William Optics FLT 91 — typical FOV & scale
- With Full-frame (36×24mm, 3.76µm)FOV: 3.82° × 2.55°Scale: 1.44"/px
- With APS-C (23.5×15.7mm, 3.76µm)FOV: 2.49° × 1.67°Scale: 1.44"/px
- With IMX533 square (11.3×11.3mm, 3.76µm)FOV: 1.20° × 1.20°Scale: 1.44"/px
William Optics RedCat 71 — recommended user
Best suited for beginners and wide-field enthusiasts running a portable travel rig.
William Optics FLT 91 — recommended user
Best suited for intermediate imagers building a versatile kit running a portable travel rig.