Askar 91F - 91mm f/6.7 Quadruplet Flat-Field APO Refractor - 91F
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Askar 91 mm Quad ED APO Flat-Field Refractor
Askar 71F Flat Field Quad Refractor Highlights
The Askar 91F is a self-flattened design that allows users to avoid calculating the back focus and buying additional flattener, 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.
With practicality and versatility in mind, the Askar 91F's weight and size are effectively controlled, making it easy to carry and use. The Askar 91F OTA weighs only 3.92kg, with a gross weight of 4.52kg (including the tube rings and dovetail plate).
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 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.
| Parameters | ||
| Aperture size | 91mm | |
| Focal length | 609mm | |
| Focal ratio | f/6.7 | |
| Objective lens | Quadruplet air-spaced APO(including one ED glass) | |
| 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 holder） 122mm（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 stretched） 550mm(including the photographic adapter as dew shield contracted） 636mm(including the photographic adapter as dew shield fully stretched） |
|
| Net weight | 3.92kg | |
| Gross weight (Including tube ring&dovetail plate) | 4.52kg | |
| Rear-end thread type | M64×1-M54×0.75 M54×0.75-M54×0.75 M54×0.75-M48×0.75 (with M48×0.75 filter thread) |
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| Standard package items | A 91F OTA，a pair of tube rings, a handle, a 230mm Vixen dovetail plate, and a set of photographic adapters | |