telescopecomparison · 2-way
William Optics RedCat 91 vs William Optics FLT 156
William Optics
RedCat 91
Best suited for beginners and wide-field enthusiasts running a portable travel rig.
William Optics
FLT 156
Best suited for intermediate imagers building a versatile kit running a backyard imaging setup.
Key differences
-54% focal length
-42% aperture
Faster by 1.5 f-stops
Specifications
| Specification | William Optics RedCat 91 | William Optics FLT 156 |
|---|---|---|
| Optics | ||
| Type | Refractor | refractor |
| Optical design | Petzval APO | Apo triplet FPL-53 |
| Aperture | 91mm | 156mm |
| Focal length | 496mm | 1085mm |
| Native f/ratio | f/5.5 | f/7.0 |
| Image circle | 45mm | 52mm |
| Full-frame support | Yes | Yes |
| Physical | ||
| Weight | 4.3kg | 11.5kg |
Advantages of William Optics RedCat 91
- Wider field — 496mm vs 1085mm focal length
- Faster optics at f/5.45 vs f/7
- Lighter (4.3kg vs 11.5kg) — easier to travel with
Advantages of William Optics FLT 156
- Tighter framing — 1085mm vs 496mm focal length
- 71% more light-gathering aperture
- Larger image circle (52mm) — supports bigger sensors
Best for — William Optics RedCat 91
- Large emission nebulae and star clusters
- Full-frame astro cameras and DSLRs
Best for — William Optics FLT 156
- Medium-sized galaxies and planetary nebulae
- 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 FLT 156 — typical FOV & scale
- With Full-frame (36×24mm, 3.76µm)FOV: 1.90° × 1.27°Scale: 0.71"/px
- With APS-C (23.5×15.7mm, 3.76µm)FOV: 1.24° × 0.83°Scale: 0.71"/px
- With IMX533 square (11.3×11.3mm, 3.76µm)FOV: 0.60° × 0.60°Scale: 0.71"/px
William Optics RedCat 91 — recommended user
Best suited for beginners and wide-field enthusiasts running a portable travel rig.
William Optics FLT 156 — recommended user
Best suited for intermediate imagers building a versatile kit running a backyard imaging setup.