telescopecomparison · 2-way
William Optics Zenithstar 81 II vs William Optics GT 102
William Optics
Zenithstar 81 II
Best suited for beginners and wide-field enthusiasts running a portable travel rig.
William Optics
GT 102
Best suited for intermediate imagers building a versatile kit running a backyard imaging setup.
Key differences
-32% focal length
-21% aperture
Faster by 1.0 f-stops
Specifications
| Specification | William Optics Zenithstar 81 II | William Optics GT 102 |
|---|---|---|
| Optics | ||
| Type | refractor | refractor |
| Optical design | Apo doublet FPL-53 | Apo triplet FPL-53 |
| Aperture | 81mm | 102mm |
| Focal length | 478mm | 703mm |
| Native f/ratio | f/5.9 | f/6.9 |
| Image circle | 44mm | 44mm |
| Full-frame support | Yes | Yes |
| Physical | ||
| Weight | 3.6kg | 5.6kg |
Advantages of William Optics Zenithstar 81 II
- Wider field — 478mm vs 703mm focal length
- Faster optics at f/5.9 vs f/6.9
- Lighter (3.6kg vs 5.6kg) — easier to travel with
Advantages of William Optics GT 102
- Tighter framing — 703mm vs 478mm focal length
- 26% more light-gathering aperture
Best for — William Optics Zenithstar 81 II
- Large emission nebulae and star clusters
- Full-frame astro cameras and DSLRs
Best for — William Optics GT 102
- Medium-sized galaxies and planetary nebulae
- Full-frame astro cameras and DSLRs
William Optics Zenithstar 81 II — 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 GT 102 — typical FOV & scale
- With Full-frame (36×24mm, 3.76µm)FOV: 2.93° × 1.96°Scale: 1.10"/px
- With APS-C (23.5×15.7mm, 3.76µm)FOV: 1.92° × 1.28°Scale: 1.10"/px
- With IMX533 square (11.3×11.3mm, 3.76µm)FOV: 0.92° × 0.92°Scale: 1.10"/px
William Optics Zenithstar 81 II — recommended user
Best suited for beginners and wide-field enthusiasts running a portable travel rig.
William Optics GT 102 — recommended user
Best suited for intermediate imagers building a versatile kit running a backyard imaging setup.