William Optics RedCat 51 II-U APO 51/250 f/4.9 astrograph (William Optics, SKU: L-RC51II-U). The RedCat 51 II-U is a compact astrograph with a four-element Petzval optical system and helical focusing. Its 250 mm focal length is suited to wide-field sky imaging, and the optical design requires no separate field flattener. The II-U version has a covered sensor tilt adjuster and camera angle rotator. It is intended for photography and is incompatible with the earlier-generation D-EP90-125-RC51-SL diagonal.
• four-element Petzval optics with a flat image field
• helical focusing mechanism with a lock
• camera rotator with a 360° range and sensor tilt adjustment
• lens cap with a Bahtinov mask
• dual-sided Vixen / Arca-Swiss mounting plate
• optical tube William Optics RedCat 51 II-U with dew shield
• lens cap with Bahtinov mask
• rotator and sensor tilt adjuster
• camera adapter M54 / M48
• mounting ring and dual-sided mounting plate
• carrying case
• optical design: Petzval, 4 elements in 3 groups
• objective diameter: 51 mm
• focal length: 250 mm
• focal ratio: f/4.9
• image circle diameter: 43 mm
• supported sensor formats: full frame, APS-C, Micro 4/3
• focusing: helical
• camera connection: M48, with M54 accessible after removing the adapter
• camera systems via a suitable optional M48 ring: Canon EF, Nikon F, Sony E, Pentax K, Micro 4/3, Fujifilm X
• rotator range: 360°
• tube length with dew shield reversed for transport: 228 mm
• tube length with dew shield in the operating position: 291 mm
• dew shield diameter: 80 mm
• optical tube weight: 1.3 kg
• weight with mounting ring and plate: 1.76 kg
• mounting: Vixen / Arca-Swiss
• colour: red
• warranty: 24 months
This helical RedCat 51 version combines a short optical tube with a flat field for wide-field astrophotography.
