telescope
William Optics
RedCat 91 WIFD
91mm Petzval (5-element advanced) · 448mm f/4.9
First model of the Ultra-Cat series; medium format capable with adapter. Previously sold as the William Optics RedCat 91; same optic under current naming.
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Product specifications can change. Please verify specifications and compatibility with the manufacturer or retailer before purchasing.
Best for
- Large emission nebulae and star clusters
- Fast imaging — short exposures per sub
- Full-frame astro cameras and DSLRs
Specifications
| Optics | |
| Type | refractor |
| Optical design | Petzval (5-element advanced) |
| Aperture | 91mm |
| Focal length | 448mm |
| Native f/ratio | f/4.9 |
| Image circle | 55mm |
| Full-frame support | Yes |
| Physical | |
| Weight | 4.7kg |
Typical FOV & image scale
With Full-frame (36×24mm, 3.76µm)
FOV 4.60° × 3.07°
Scale 1.73″/px
With APS-C (23.5×15.7mm, 3.76µm)
FOV 3.01° × 2.01°
Scale 1.73″/px
With IMX533 square (11.3×11.3mm, 3.76µm)
FOV 1.45° × 1.45°
Scale 1.73″/px
Recommended accessories
- William Optics Flat 6AIIIflattener · 1× focal lengthUse with this telescopecommunity reported
Typical targets
- IC 434 — Horsehead NebulaEmission Nebula · 60′Plan this target
- NGC 869/884 — Double ClusterOpen Cluster · 60′Plan this target
- NGC 2264 — Christmas Tree ClusterEmission Nebula · 60′Plan this target
- NGC 6992 — Eastern VeilSupernova Remnant · 60′Plan this target
- NGC 7822 — Cepheus HII RegionEmission Nebula · 60′Plan this target
- Sh2-132 — Lion NebulaEmission Nebula · 60′Plan this target
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Source: williamoptics.com