telescope
William Optics
RedCat 51
51mm Petzval APO · 250mm f/4.9
Native flat-field Petzval; wide-field astrograph.
Best for
- Wide-field nebulae and Milky Way regions
- Fast imaging — short exposures per sub
- Full-frame astro cameras and DSLRs
Specifications
| Optics | |
| Type | Refractor |
| Optical design | Petzval APO |
| Aperture | 51mm |
| Focal length | 250mm |
| Native f/ratio | f/4.9 |
| Image circle | 45mm |
| Full-frame support | Yes |
| Physical | |
| Weight | 1.6kg |
Typical FOV & image scale
With Full-frame (36×24mm, 3.76µm)
FOV 8.25° × 5.50°
Scale 3.10″/px
With APS-C (23.5×15.7mm, 3.76µm)
FOV 5.39° × 3.60°
Scale 3.10″/px
With IMX533 square (11.3×11.3mm, 3.76µm)
FOV 2.59° × 2.59°
Scale 3.10″/px
Recommended accessories
- William Optics Flat 6AIIIflattener · 1× focal lengthcommunity reported
- William Optics RedCat 51 Flattener (built-in)flattener · 1× focal lengthmanufacturer supported
Typical targets
- Messier M45 — PleiadesReflection Nebula · 110′
- NGC NGC 7000 — North America NebulaEmission Nebula · 120′
- IC IC 2177 — Seagull NebulaEmission Nebula · 120′
- Messier M44 — Beehive ClusterOpen Cluster · 95′
- Messier M8 — Lagoon NebulaEmission Nebula · 90′
- Messier M24 — Sagittarius Star CloudOpen Cluster · 90′
Recommended cameras
28.4mm sensor · 4.78µm px · cooled
Compare pairing28.3mm sensor · 3.76µm px · cooled
Compare pairing28.3mm sensor · 3.76µm px · cooled
Compare pairing