William Optics Apochromatic refractor AP 91/448 BlackCat 91 WIFD OTA (85223)

The AP 91/448 is an outstanding optical instrument that combines a compact form, attractive price, and excellent optical performance—perfect for both astrophotographers and nature photographers. Its heart is a Petzval design featuring four elements in three groups, made from premium FPL53 and FPL51 glass. This configuration produces a color-accurate, well-corrected image field with a diameter of over 55mm, making it ideal for full-frame cameras. Its fast f/4.9 aperture enables short exposure times.

Both M48 and M54 camera threads are available, with two compatible adapters included in the package. The focuser uses a helical design: simply rotate the textured focusing ring on the tube for precise adjustments. This internal focusing system easily handles even heavy cameras. The BlackCat 91 uses William Optics’ “WIFD” (With Internal Focus Design), meaning all focusing happens inside the tube.

The included prism rail offers two mounting methods: screw it on using a photo thread or mount it with either Arca-Swiss or Losmandy standards. These options make it easy to attach the telescope to all typical photo tripods, camera mounts, or astronomy mounts.

The BlackCat 91 comes with a durable nylon carrying case and a specially designed Bahtinov mask for accurate focusing, which is permanently integrated into the lens assembly.

Optics like the Cat 91 are ideal not only for photographing the night sky, but also for wildlife photography. With the Cat 91, you’ll enjoy superb optical quality alongside the robust and elegant finish for which William Optics is renowned.

Specifications

Optics

• Type: Refractor (Apochromat)

• Aperture: 91mm

• Focal length: 448mm

• Aperture ratio: f/4.9

• Resolving power: 1.52 arcseconds

• Limiting magnitude: 12.3

• Light gathering power: 170x

• Maximum useful magnification: 182x

• Tube weight: 6.3kg

• Tube length: 556mm

• Tube material: Aluminum

• Coating: Multi-coated

• Tube design: Full tube

• Lens design: Quadruplet (4 elements)

Focuser

• Tilting adapter: Yes

• Type: Helical, internal focusing

• Camera thread: M48 / M54

• Clear aperture: 55mm

• Rotatable: Yes

Mount

• Optical Tube Assembly (OTA) only—no mount included

Included Accessories

• Dew shield: Yes

• Carry case: Yes

• Integrated Bahtinov focusing mask: Yes

• Prism rail: Yes (Arca-Swiss & Losmandy compatible)

• Camera tripod thread: Yes

• Integrated field corrector: Yes

• Eyepiece adapter: 1.25" & 2"

General

• Series: Cat

• Color: Black

Applications

• Astrophotography: Yes (excellent)

• Moon & planets: Yes

• Nature observation: Yes

• Nebulae & galaxies: Yes

• Sun: No (unless equipped with a proper solar filter)

Recommended for

• Beginners: No

• Advanced users: Yes

• Observatories: No