The Askar 91F is an OTA with an aperture of 91mm, a focal length of 609mm, and a native focal ratio of F/6.7, designed for astronomy enthusiasts who prioritize portability, high optical quality, and ease of use, offering a flat-field, full-frame-capable APO refractor ideal for wide-field imaging and daytime spotting. The optical design of the Askar 91F features a four-element configuration (three elements in the front and one in the rear), including one piece of ED glass, which can effectively reduce chromatic aberration. The Askar 91F supports 44mm full-frame imaging with great performance of the surrounding star points. The Askar 91F is a self-flattened design that allows users to avoid calculating the back focus and buying additional flatteners. After attaching the imaging accessories, users can directly use it for shooting after the OTA is in focus. This further reduces the cost and improves the pleasure of shooting. The Askar 91F strikes a balance between practicality and versatility while achieving lightweight portability through its compact design.The OTA weighs just 3.92kg, with a gross weight of 4.52kg (including the tube rings and dovetail plate). The Askar 91F is versatile in its use, allowing for both visual observation and astrophotography. The Askar 91F comes standard with a photographic extension tube with a built-in 2-inch filter thread for easy shooting connections, providing M48×0.75 & M54×0.75 adapters to accommodate various DSLR cameras and professional astronomical cameras, meeting diverse imaging needs. The mechanical design of the Askar 91F itself adheres to Askar's consistent philosophy of taking into account the user's habits and minimizing the user's invisible costs. The Askar 91F features a retractable dew shield, further reducing overall length and enhancing portability.The inside of the tube is pasted with matting felt to better eliminate stray light, while the exterior sports a sleek blue-and-white color scheme with high-quality CNC machining and paint finish. The Askar 91F's handle is 130mm long and has a finder base slot. Besides, there are two finder bases on both sides of the focuser, which not only eliminates the need for disassembling when changing the position of the finder scope but also provides additional mounting positions for other astronomical accessories. In terms of the focuser, the Askar 91F is equipped with a dual-speed R&P 3-inch rigid focuser, which has a 1:10 fine adjustment and a 360° scaled rotator at the rear end for precise angle adjustment.The 230mm Vixen-style dovetail plate includes 1/4" and 3/8" screw holes for direct tripod mounting. The rear interface of the Askar 91F includes both 2-inch and 1.25-inch adapters, enabling compatibility with a wide range of astronomical accessories. Whether for deep-sky astrophotography, planetary observation, or birdwatching and travel, the 91F is your ideal companion for exploring the world. Specifications Aperture Size 91mm Focal Length 609mm Focal Ratio f/6.7 Objective Lens Quadruplet air-spaced APO (including one ED glass element) Image Circle 44mm Maximum Accessory Connection(with the Focuser Fully Retreated) Imaging Mode:75mm (from the base of M48×0.75 male thread)93mm（from the base of M54×0.75 male thread) Observing Mode:112mm（from the end of 1.25" eyepiece holder122mm（from the end of 2" eyepiece holder) Total Length 513mm(including 1.25" adapter as dew shield contracted)599mm(including 1.25" adapter as dew shield fully extended)550mm(including the photographic adapter as dew shield contracted)636mm(including the photographic adapter as dew shield fully extended) Net Weight 3.92kg Gross Weight(Including Tube Ring & Dovetail Plate) 4.52kg Rear-End Thread Type M64×1-M54×0.75M54×0.75-M54×0.75M54×0.75-M48×0.75 (with M48×0.75 filter thread) Product Size Diagram 60F Connection Diagram The Locking Screw Position Diagram EAF (optional) Installation Optical Path Diagram Spot Diagram
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