telescopecomparison · 2-way
William Optics GT 102 vs Borg 90FL
William Optics
GT 102
Best suited for intermediate imagers building a versatile kit running a backyard imaging setup.
Key differences
+41% focal length
+13% aperture
Slower by 1.3 f-stops
Specifications
| Specification | William Optics GT 102 | Borg 90FL |
|---|---|---|
| Optics | ||
| Type | refractor | refractor |
| Optical design | Apo triplet FPL-53 | Apo doublet fluorite |
| Aperture | 102mm | 90mm |
| Focal length | 703mm | 500mm |
| Native f/ratio | f/6.9 | f/5.6 |
| Image circle | 44mm | — |
| Full-frame support | Yes | No |
| Physical | ||
| Weight | 5.6kg | 2.5kg |
Advantages of William Optics GT 102
- Tighter framing — 703mm vs 500mm focal length
- 13% more light-gathering aperture
- Larger image circle (44mm) — supports bigger sensors
Advantages of Borg 90FL
- Wider field — 500mm vs 703mm focal length
- Faster optics at f/5.6 vs f/6.9
- Lighter (2.5kg 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 — Borg 90FL
- Large emission nebulae and star clusters
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
Borg 90FL — typical FOV & scale
- With Full-frame (36×24mm, 3.76µm)FOV: 4.13° × 2.75°Scale: 1.55"/px
- With APS-C (23.5×15.7mm, 3.76µm)FOV: 2.69° × 1.80°Scale: 1.55"/px
- With IMX533 square (11.3×11.3mm, 3.76µm)FOV: 1.29° × 1.29°Scale: 1.55"/px
William Optics GT 102 — recommended user
Best suited for intermediate imagers building a versatile kit running a backyard imaging setup.
Borg 90FL — recommended user
Best suited for beginners and wide-field enthusiasts running a portable travel rig.