telescope
William Optics
RedCat 91
91mm Petzval APO · 496mm f/5.5
Petzval astrograph; native full-frame.
Best for
- Large emission nebulae and star clusters
- Full-frame astro cameras and DSLRs
Specifications
| Optics | |
| Type | Refractor |
| Optical design | Petzval APO |
| Aperture | 91mm |
| Focal length | 496mm |
| Native f/ratio | f/5.5 |
| Image circle | 45mm |
| Full-frame support | Yes |
| Physical | |
| Weight | 4.3kg |
Typical FOV & image scale
With Full-frame (36×24mm, 3.76µm)
FOV 4.16° × 2.77°
Scale 1.56″/px
With APS-C (23.5×15.7mm, 3.76µm)
FOV 2.71° × 1.81°
Scale 1.56″/px
With IMX533 square (11.3×11.3mm, 3.76µm)
FOV 1.31° × 1.31°
Scale 1.56″/px
Recommended accessories
- William Optics Flat 6AIIIflattener · 1× focal lengthcommunity reported
Typical targets
- IC IC 434 — Horsehead NebulaEmission Nebula · 60′
- NGC NGC 869/884 — Double ClusterOpen Cluster · 60′
- NGC NGC 2264 — Christmas Tree ClusterEmission Nebula · 60′
- NGC NGC 6992 — Eastern VeilSupernova Remnant · 60′
- NGC NGC 7822 — Cepheus HII RegionEmission Nebula · 60′
- Messier M48 — Open Cluster M48Open Cluster · 54′
Recommended cameras
28.4mm sensor · 4.78µm px · cooled
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Compare pairing28.3mm sensor · 3.76µm px · cooled
Compare pairing