telescopecomparison · 2-way
William Optics Zenithstar 73 II vs William Optics GT 81
William Optics
Zenithstar 73 II
Best suited for beginners and wide-field enthusiasts running a portable travel rig.
William Optics
GT 81
Best suited for beginners and wide-field enthusiasts running a portable travel rig.
Key differences
-10% focal length
-10% aperture
Specifications
| Specification | William Optics Zenithstar 73 II | William Optics GT 81 |
|---|---|---|
| Optics | ||
| Type | refractor | refractor |
| Optical design | Apo doublet FPL-53 | Apo triplet FPL-53 |
| Aperture | 73mm | 81mm |
| Focal length | 430mm | 478mm |
| Native f/ratio | f/5.9 | f/5.9 |
| Image circle | 44mm | 44mm |
| Full-frame support | No | Yes |
| Physical | ||
| Weight | 2.4kg | 3.8kg |
Advantages of William Optics Zenithstar 73 II
- Wider field — 430mm vs 478mm focal length
- Lighter (2.4kg vs 3.8kg) — easier to travel with
Advantages of William Optics GT 81
- Tighter framing — 478mm vs 430mm focal length
- 11% more light-gathering aperture
Best for — William Optics Zenithstar 73 II
- Large emission nebulae and star clusters
Best for — William Optics GT 81
- Large emission nebulae and star clusters
- Full-frame astro cameras and DSLRs
William Optics Zenithstar 73 II — typical FOV & scale
- With Full-frame (36×24mm, 3.76µm)FOV: 4.80° × 3.20°Scale: 1.80"/px
- With APS-C (23.5×15.7mm, 3.76µm)FOV: 3.13° × 2.09°Scale: 1.80"/px
- With IMX533 square (11.3×11.3mm, 3.76µm)FOV: 1.51° × 1.51°Scale: 1.80"/px
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
William Optics Zenithstar 73 II — recommended user
Best suited for beginners and wide-field enthusiasts running a portable travel rig.
William Optics GT 81 — recommended user
Best suited for beginners and wide-field enthusiasts running a portable travel rig.