Redcat 91 review by AstroBackyard

The William Optics RedCat 91 is an apochromatic refractor designed for astrophotography. Its 5-element Petzval design eliminates the need for backfocus adjustments, providing sharp, edge-to-edge images. The telescope is compatible with full-frame and medium-format cameras, offering a 50mm image circle and flat-field optics that do not require an additional flattener. Its fast f/4.9 focal ratio allows for better light-gathering and sharp images of faint celestial objects.

The RedCat 91 offers precise and stable focusing with its WIFD focuser system, which avoids tube tilt caused by accessories. The telescope includes a Bahtinov mask, tilt adjuster, and camera angle rotator to simplify adjustments. Its compact size and lightweight build, along with the included handlebar and stable mounting ring, make it easy to use and transport, suitable for both beginners and experienced astrophotographers. The RedCat 91 combines efficient optics with a practical design for astrophotography.

William Optics RedCat 91 specifications:

• Lens Type: 5-Element Advanced Petzval
• Lens Elements: Super ED Glass x2, ED Glass x1, Lanthanum Glass x1, X-Element x1
• Focal Length: 448 mm
• Diameter: 91 mm
• Focal Ratio: f/4.9
• Image Circle: 55 mm
• Focuser: WIFD R&P Focuser, Compatible with EAF
• Flange Distance: Maximum M48 (60.8mm), M54 (65.8mm)
• Focus Travel: 0-36mm (Ruler to 40mm)
• Adapter Included: Tilt Adjuster, Rotator, M63 → M54 Adapter, M63 → M48 Adapter
• Optional Flattener: No Flattener Required
• T-Mount Supported: Canon EF, RF, Nikon F, Z, Sony E, Pentax K, MFT (M4/3), FUJI X
• Camera Format: Medium Format (additional adapter required), Full Frame, APS-C, M4/3
• Tube Length: 556 mm
• OTA Weight: 4.72 kg / 10.41 lbs
• Total Weight: 6.3 kg / 13.89 lbs

The RedCat 91 has several features designed for astrophotography. Its Petzval design allows for sharp images without backfocus adjustments, and it works with full-frame and medium-format cameras without needing an additional flattener. The f/4.9 focal ratio improves light-gathering, making it easier to capture faint objects. The WIFD focuser system ensures stable focusing, and the included Bahtinov mask and tilt adjuster simplify fine adjustments. Its compact design, handlebar, and mounting ring make it easy to use and transport.

Redcat 91 review by AstroBackyard

Astrophotographer Trevor Jones conducted a first-light test of the new William Optics Redcat 91 telescope. The session focused on imaging the Pleiades star cluster under challenging conditions, including subzero temperatures and intermittent cloud cover. This review provided insights into the telescope's performance, highlighting both its strengths and areas for improvement. Jones noted that the telescope's optical quality was excellent, with no visible distortions or optical flaws in his test images. The built-in Bahtinov mask and sturdy construction were among the features he appreciated.

Initial results included single-frame and stacked exposures

For this test, Jones used the telescope with a ZWO ASI2600MM Pro camera and an AM5 mount, capturing luminance and RGB data with 120-second exposures. He operated the setup remotely using ASIAIR in station mode, which allowed seamless control from within his home. The telescope successfully executed a Meridian flip during his absence, but clouds ultimately cut the imaging session short.

The initial results included single-frame and stacked exposures. Despite limited data, Jones praised the telescope’s ability to handle bright stars in the Pleiades without introducing noticeable aberrations. However, he observed that the telescope's potential was somewhat constrained by his crop-sensor camera, as one of the Redcat 91's selling points is its compatibility with larger sensors.

Areas for improvement in his setup

Jones noted several areas for improvement in his setup. He plans to add an electronic focuser to maintain focus during extended sessions and a camera rotator for better composition control. Cable management also proved challenging in the extreme cold, prompting a need for refinement to ensure smooth operation.

Redcat 91’s suitability for mid-range astrophotography

The review underscored the Redcat 91’s suitability for mid-range astrophotography targets, particularly in demanding optical tests. While Jones faced obstacles due to weather and equipment limitations, his first impressions of the telescope were largely positive, citing sharp optics and robust design as key strengths.

AstroBackyard’s review highlights the Redcat 91 as a promising addition to the William Optics lineup, appealing to both amateur and experienced astrophotographers seeking a versatile and high-quality refractor. The telescope’s performance under challenging conditions reflects its potential for capturing detailed and accurate celestial images.

William Optics REDCAT 91 FIRST LIGHT!

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