Sky-Watcher Classic 200P

Sky-Watcher Classic 200P: An 8-inch f/5.9 Dobsonian

John Dobson popularized this simple alt-azimuth mount for Newtonian reflectors in the late 1970s. You swivel the tube in azimuth and tilt it in altitude; because the Earth rotates, you nudge it in both axes to keep an object in the field.

Traditional Dobsonians are recommended for first-time buyers. The mount points by hand and needs no power.

Paraboloidal Mirror and Secondary Support

A paraboloidal primary mirror eliminates spherical aberration, with a four-arm secondary mirror bracket on fine 0.5 mm supports to reduce diffraction. The highest practical power is 406x.

• Primary mirror: paraboloidal, 203mm, 1200mm focal length (f/5.9).
• Secondary mirror: 47 mm, on a four-arm bracket with 0.5 mm supports.

60x and 96x Magnification with 2 Included Eyepieces

Magnification is the telescope's focal length divided by the eyepiece focal length: the included 20 mm and 12.5 mm 1.25-inch eyepieces give 60x and 96x. Sky-Watcher's rule of thumb for usable magnification is about 2x per mm of aperture in good conditions.

• Magnification Formula: Telescope Focal Length / Eyepiece Focal Length.
• 20 mm eyepiece: 1200 / 20 = 60x.
• 12.5 mm eyepiece: 1200 / 12.5 = 96x.

The 2-Piece Dobsonian Base with Patented Tension Control

A Dobsonian mount holds the tube by friction. Sky-Watcher's patented tension control handle adds or reduces friction between the tube and the side board, so the tube does not need to be balanced to stay in position.

Loosen or tighten the handle to add just enough friction for the tube to move easily when nudged but stay in position when not. Re-adjust it when you add or remove accessories. Install it on the same side as the focuser, and leave the handle on the other side slightly loose. Tightened fully, it locks the tube.

Focuser, Eyepieces and Finder

The 2-inch focuser takes 2-inch eyepieces, and a 1.25-inch adapter is included for the supplied eyepieces.

The finderscope mounts on the tube and has a wider field than the main telescope, for centering a target. Focusing: turn the focus knobs until the image is sharp, and refocus after changing an eyepiece or as the temperature changes.

Assembly Guide: Building the 2-Piece Base for the 200P

The flat-packed base is assembled once, ideally in daylight and in a large, open area. Connect side boards A1 and A2 to board B with the Sky-Watcher logos outside, then attach this to the round top board (C).

The Teflon pad goes between the top board and the round bottom board (D), joined by a central bolt; do not over-tighten it. Then fit the four cylindrical saddle side bearings, accessory tray and carrying handle. The tube's side bearings rest on the saddle bearings.

Aligning the Finderscope

Before you can use the finderscope to locate objects, it must be aligned with the main telescope. This is best done during the day. First, insert an eyepiece into the main telescope and point it at a distant, stationary object at least 500 yards (or meters) away. Center the object in the main eyepiece.

Next, look through the finderscope. Use the two small alignment screws on the finder bracket to move the finderscope's crosshairs until they are also centered on the exact same object. These screws work against a spring-loaded knob. Once the object is centered in both the finderscope and the main eyepiece, the alignment is complete. Objects you center in the finder will now appear in the field of view of your main telescope.

Cool-Down and Observing Site

Telescopes need at least 10 to 30 minutes to cool to outside air temperature, longer with a big temperature difference or larger optics. Cooling minimizes heat-wave distortion inside the tube (tube currents).

Choose a site away from city lights, as high as possible, with a dark, unobstructed horizon; the darkest sky is usually at the zenith. Expose your eyes to nothing but red light for 30 minutes before observing.

Collimation and Care

Collimation aligns the telescope's mirrors. Check it on a slightly defocused star: symmetrical rings around the central disc mean the optics are aligned.

If the rings are lopsided, adjustment is needed. The secondary mirror is adjusted using the central bolt and three small surrounding screws on the spider hub. The primary mirror is adjusted using three adjusting screws on the back of the telescope, which are secured by three locking screws. The manual walks through both mirrors. When not in use, always replace the dust cap to keep the optics clean.

Tube and Base

The tube weighs 11 kg (24.3 lb), is 112 cm (44 in) long and 20.5 cm in diameter, and lifts off the Dobsonian base, so they move as two pieces.

Replace the dust cap whenever the telescope is not in use. Do not clean the mirror unless you are familiar with optical surfaces; clean the finderscope and eyepieces only with lens paper.

Solar Safety

Looking directly at the Sun through the telescope will cause permanent eye damage. Use a proper solar filter for viewing the Sun.

Never use an eyepiece-type solar filter. Never use the telescope to project sunlight onto another surface: the internal heat build-up will damage the optical elements. When observing the Sun, place a dust cap over the finderscope to protect it from exposure.