telescopecomparison · 2-way
William Optics RedCat 91 vs William Optics GT 71
William Optics
RedCat 91
Best suited for beginners and wide-field enthusiasts running a portable travel rig.
William Optics
GT 71
Best suited for beginners and wide-field enthusiasts running a portable travel rig.
Key differences
+18% focal length
+28% aperture
Faster by 0.5 f-stops
Specifications
| Specification | William Optics RedCat 91 | William Optics GT 71 |
|---|---|---|
| Optics | ||
| Type | Refractor | refractor |
| Optical design | Petzval APO | Apo triplet FPL-53 |
| Aperture | 91mm | 71mm |
| Focal length | 496mm | 420mm |
| Native f/ratio | f/5.5 | f/5.9 |
| Image circle | 45mm | 44mm |
| Full-frame support | Yes | Yes |
| Physical | ||
| Weight | 4.3kg | 3.4kg |
Advantages of William Optics RedCat 91
- Tighter framing — 496mm vs 420mm focal length
- 28% more light-gathering aperture
- Faster optics at f/5.45 vs f/5.9
Advantages of William Optics GT 71
- Wider field — 420mm vs 496mm focal length
- Lighter (3.4kg vs 4.3kg) — easier to travel with
Best for — William Optics RedCat 91
- Large emission nebulae and star clusters
- Full-frame astro cameras and DSLRs
Best for — William Optics GT 71
- 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
William Optics GT 71 — typical FOV & scale
- With Full-frame (36×24mm, 3.76µm)FOV: 4.91° × 3.27°Scale: 1.85"/px
- With APS-C (23.5×15.7mm, 3.76µm)FOV: 3.21° × 2.14°Scale: 1.85"/px
- With IMX533 square (11.3×11.3mm, 3.76µm)FOV: 1.54° × 1.54°Scale: 1.85"/px
William Optics RedCat 91 — recommended user
Best suited for beginners and wide-field enthusiasts running a portable travel rig.
William Optics GT 71 — recommended user
Best suited for beginners and wide-field enthusiasts running a portable travel rig.