telescopecomparison · 2-way
William Optics GT 102 vs William Optics GT 81
William Optics
GT 102
Best suited for intermediate imagers building a versatile kit running a backyard imaging setup.
William Optics
GT 81
Best suited for beginners and wide-field enthusiasts running a portable travel rig.
Key differences
+47% focal length
+26% aperture
Slower by 1.0 f-stops
Specifications
| Specification | William Optics GT 102 | William Optics GT 81 |
|---|---|---|
| Optics | ||
| Type | refractor | refractor |
| Optical design | Apo triplet FPL-53 | Apo triplet FPL-53 |
| Aperture | 102mm | 81mm |
| Focal length | 703mm | 478mm |
| Native f/ratio | f/6.9 | f/5.9 |
| Image circle | 44mm | 44mm |
| Full-frame support | Yes | Yes |
| Physical | ||
| Weight | 5.6kg | 3.8kg |
Advantages of William Optics GT 102
- Tighter framing — 703mm vs 478mm focal length
- 26% more light-gathering aperture
Advantages of William Optics GT 81
- Wider field — 478mm vs 703mm focal length
- Faster optics at f/5.9 vs f/6.9
- Lighter (3.8kg vs 5.6kg) — easier to travel with
Best for — William Optics GT 102
- Medium-sized galaxies and planetary nebulae
- Full-frame astro cameras and DSLRs
Best for — William Optics GT 81
- Large emission nebulae and star clusters
- Full-frame astro cameras and DSLRs
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 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 GT 102 — recommended user
Best suited for intermediate imagers building a versatile kit running a backyard imaging setup.
William Optics GT 81 — recommended user
Best suited for beginners and wide-field enthusiasts running a portable travel rig.