telescopecomparison · 2-way
William Optics Zenithstar 81 II vs Askar FRA400
William Optics
Zenithstar 81 II
Best suited for beginners and wide-field enthusiasts running a portable travel rig.
Key differences
+20% focal length
+13% aperture
Slower by 0.3 f-stops
Specifications
| Specification | William Optics Zenithstar 81 II | Askar FRA400 |
|---|---|---|
| Optics | ||
| Type | refractor | Refractor |
| Optical design | Apo doublet FPL-53 | Petzval Quintuplet APO |
| Aperture | 81mm | 72mm |
| Focal length | 478mm | 400mm |
| Native f/ratio | f/5.9 | f/5.6 |
| Image circle | 44mm | 44mm |
| Full-frame support | Yes | Yes |
| Physical | ||
| Weight | 3.6kg | 3.9kg |
Advantages of William Optics Zenithstar 81 II
- Tighter framing — 478mm vs 400mm focal length
- 13% more light-gathering aperture
Advantages of Askar FRA400
- Wider field — 400mm vs 478mm focal length
- Faster optics at f/5.6 vs f/5.9
Best for — William Optics Zenithstar 81 II
- Large emission nebulae and star clusters
- Full-frame astro cameras and DSLRs
Best for — Askar FRA400
- Large emission nebulae and star clusters
- 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
Askar FRA400 — typical FOV & scale
- With Full-frame (36×24mm, 3.76µm)FOV: 5.16° × 3.44°Scale: 1.94"/px
- With APS-C (23.5×15.7mm, 3.76µm)FOV: 3.37° × 2.25°Scale: 1.94"/px
- With IMX533 square (11.3×11.3mm, 3.76µm)FOV: 1.62° × 1.62°Scale: 1.94"/px
William Optics Zenithstar 81 II — recommended user
Best suited for beginners and wide-field enthusiasts running a portable travel rig.
Askar FRA400 — recommended user
Best suited for beginners and wide-field enthusiasts running a portable travel rig.