telescopecomparison · 2-way
William Optics GT 81 vs William Optics Zenithstar 61 II
William Optics
GT 81
Best suited for beginners and wide-field enthusiasts running a portable travel rig.
William Optics
Zenithstar 61 II
Best suited for beginners and wide-field enthusiasts running a portable travel rig.
Key differences
+33% focal length
+33% aperture
Specifications
| Specification | William Optics GT 81 | William Optics Zenithstar 61 II |
|---|---|---|
| Optics | ||
| Type | refractor | refractor |
| Optical design | Apo triplet FPL-53 | Apo doublet FPL-53 |
| Aperture | 81mm | 61mm |
| Focal length | 478mm | 360mm |
| Native f/ratio | f/5.9 | f/5.9 |
| Image circle | 44mm | 44mm |
| Full-frame support | Yes | No |
| Physical | ||
| Weight | 3.8kg | 1.9kg |
Advantages of William Optics GT 81
- Tighter framing — 478mm vs 360mm focal length
- 33% more light-gathering aperture
Advantages of William Optics Zenithstar 61 II
- Wider field — 360mm vs 478mm focal length
- Lighter (1.9kg vs 3.8kg) — easier to travel with
Best for — William Optics GT 81
- Large emission nebulae and star clusters
- Full-frame astro cameras and DSLRs
Best for — William Optics Zenithstar 61 II
- Large emission nebulae and star clusters
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 61 II — typical FOV & scale
- With Full-frame (36×24mm, 3.76µm)FOV: 5.73° × 3.82°Scale: 2.15"/px
- With APS-C (23.5×15.7mm, 3.76µm)FOV: 3.74° × 2.50°Scale: 2.15"/px
- With IMX533 square (11.3×11.3mm, 3.76µm)FOV: 1.80° × 1.80°Scale: 2.15"/px
William Optics GT 81 — recommended user
Best suited for beginners and wide-field enthusiasts running a portable travel rig.
William Optics Zenithstar 61 II — recommended user
Best suited for beginners and wide-field enthusiasts running a portable travel rig.