telescope
William Optics
FLT 91
91mm Triplet APO · 540mm f/5.9
FPL-53 triplet; use with dedicated flattener for FF.
Best for
- Large emission nebulae and star clusters
- Full-frame astro cameras and DSLRs
Specifications
| Optics | |
| Type | Refractor |
| Optical design | Triplet APO |
| Aperture | 91mm |
| Focal length | 540mm |
| Native f/ratio | f/5.9 |
| Image circle | 44mm |
| Full-frame support | Yes |
| Physical | |
| Weight | 4.5kg |
Typical FOV & image scale
With Full-frame (36×24mm, 3.76µm)
FOV 3.82° × 2.55°
Scale 1.44″/px
With APS-C (23.5×15.7mm, 3.76µm)
FOV 2.49° × 1.67°
Scale 1.44″/px
With IMX533 square (11.3×11.3mm, 3.76µm)
FOV 1.20° × 1.20°
Scale 1.44″/px
Recommended accessories
- William Optics Adjustable Flat 6AIII 0.8xreducer · 0.8× focal lengthmanufacturer supported
Typical targets
- Messier M48 — Open Cluster M48Open Cluster · 54′
- NGC NGC 6357 — Lobster NebulaEmission Nebula · 50′
- IC IC 443 — Jellyfish NebulaSupernova Remnant · 50′
- Messier M17 — Omega NebulaEmission Nebula · 46′
- NGC NGC 1893 — Emission Nebula NGC 1893Emission Nebula · 45′
- IC IC 434 — Horsehead NebulaEmission Nebula · 60′
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