Sky-Watcher 10" f/3.94 Quattro Imaging Newtonian Telescope (OTA Only) Sky-Watcher's 10" f/3.94 Quattro Imaging Newtonian Telescope has been specifically engineered for astrophotography and astro-imaging performance. Its 1000mm focal length has been shortened to produce a fast f/3.94 focal ratio which helps to reduce the exposure times required for capturing detailed images of the Moon, planets, and deep-sky objects. To further help boost its performance are borosilicate mirrors which have a low coefficient of thermal expansion to reduce the effects of expansion/contraction due to temperature fluctuation. This helps limit distortion that can occur when moving the OTA from indoors to outdoors and limiting the scope's ability to resolve details. The entire optical system is fully multicoated to increase the reflectivity of all surfaces to produce brighter and sharper images. For imaging and visual use, the ability to achieve tack-sharp focus is critical, so Sky-Watcher outfitted the Quattro with a large Crayford-style focuser. This design uses a steel rod held tightly against the focus tube under tension. Using this toothless friction system eliminates backlash and enables ultra-fine precision focusing. A large coarse-focus wheel quickly brings subjects into rough focus, and then the 10:1 fine-focus allows the user to precisely focus it without the risk of losing it as soon as the knob is released. Having the ability to use larger 2" accessories and eyepieces provides an immersive experience during observation sessions and the ability to use larger sensors for capturing images, and a reducer adapter is included if you want to use the more common 1.25" eyepieces. Features: SkyWatcher QUATTRO-250P 250mm F/4 Dual-Speed Parabolic Newtonian Telescope Pyrex Mirrors 2" Dual-speed Linear Power Parabolic Primary Mirrors Sky-watcher Deluxe Mirror Coatings F/4 Focal Ratios 10:1 Speed Reduction 56% More Light-gathering Than 200mm Specificatons: SkyWatcher QUATTRO-250P 250mm F/4 Dual-Speed Parabolic Newtonian Telescope Manufacturer: SkyWatcher Condition: New Warranty: 2 Year Highest Practical Power (Potential): x508 Diameter of Primary Mirror: 254mm Telescope Focal Length: 1000mm (f/4) Primary Mirror: Parabolic (Pyrex) Power Focuser: 2" (50.8mm) Dual-Speed 10:1 Linear Mirror: 0.5mm Ultra-Thin Secondary Mirror Supports PS Finderscope: NO