telescopecomparison · 2-way
William Optics GT 81 vs Radian Raptor 75
William Optics
GT 81
Best suited for beginners and wide-field enthusiasts running a portable travel rig.
Key differences
+18% focal length
+8% aperture
Slower by 0.5 f-stops
Specifications
| Specification | William Optics GT 81 | Radian Raptor 75 |
|---|---|---|
| Optics | ||
| Type | refractor | refractor |
| Optical design | Apo triplet FPL-53 | Petzval quintuplet |
| Aperture | 81mm | 75mm |
| Focal length | 478mm | 405mm |
| Native f/ratio | f/5.9 | f/5.4 |
| Image circle | 44mm | 44mm |
| Full-frame support | Yes | Yes |
| Physical | ||
| Weight | 3.8kg | 4.5kg |
Advantages of William Optics GT 81
- Tighter framing — 478mm vs 405mm focal length
- Lighter (3.8kg vs 4.5kg) — easier to travel with
Advantages of Radian Raptor 75
- Wider field — 405mm vs 478mm focal length
- Faster optics at f/5.4 vs f/5.9
Best for — William Optics GT 81
- Large emission nebulae and star clusters
- Full-frame astro cameras and DSLRs
Best for — Radian Raptor 75
- Large emission nebulae and star clusters
- Full-frame astro cameras and DSLRs
William Optics GT 81 — typical FOV & scale
- With Full-frame (36×24mm, 3.76µm)FOV: 4.32° × 2.88°Scale: 1.62"/px
- With APS-C (23.5×15.7mm, 3.76µm)FOV: 2.82° × 1.88°Scale: 1.62"/px
- With IMX533 square (11.3×11.3mm, 3.76µm)FOV: 1.35° × 1.35°Scale: 1.62"/px
Radian Raptor 75 — typical FOV & scale
- With Full-frame (36×24mm, 3.76µm)FOV: 5.09° × 3.40°Scale: 1.91"/px
- With APS-C (23.5×15.7mm, 3.76µm)FOV: 3.32° × 2.22°Scale: 1.91"/px
- With IMX533 square (11.3×11.3mm, 3.76µm)FOV: 1.60° × 1.60°Scale: 1.91"/px
William Optics GT 81 — recommended user
Best suited for beginners and wide-field enthusiasts running a portable travel rig.
Radian Raptor 75 — recommended user
Best suited for beginners and wide-field enthusiasts running a portable travel rig.