Explore Scientific 6-inch Tabletop Dobsonian Reflector Telescope

The Explore Scientific ES-ON15205TT: A 152mm f/5 Grab-and-Go Telescope

The 6-inch Tabletop Dobsonian is designed for observers who want serious aperture without the complexity of a traditional equatorial mount or the bulk of a full-sized Dobsonian. It suits a beginner, showing the Moon and planets and reaching bright galaxies and nebulae from darker skies.

For an experienced observer it is a quick-setup second telescope: the tube is 686mm (27 inches) long, and the base needs no alignment.

Parabolic Optics: The 152mm Mirror and f/5 Focal Ratio

The heart of this telescope is its 152mm (6-inch) parabolic primary mirror. A paraboloid figure avoids the spherical aberration of a spherical mirror. The mirror is aluminum coated with an SiO2 overcoat.

The optical system's 760mm focal length results in a fast f/5 focal ratio. With the 25mm Plössl at 30x the field is wide enough for the Pleiades star cluster (M45) and the bright core of the Andromeda Galaxy (M31). The 53mm secondary mirror gives a central obstruction of 34.9% by diameter.

From M42 to Saturn's Rings: Observing with 152mm of Aperture

The farther you are from city lights, the more you will see.

• The Moon: See craters, mountain ranges and rilles. Watch the terminator (the line between light and shadow) move from night to night, revealing new features in sharp relief.
• The Planets: See the rings of Saturn, spot the main cloud belts on Jupiter and track its four Galilean moons, and follow the phases of Venus. Under steady skies, you may even glimpse the polar ice caps on Mars.
• Deep Sky Objects: From a reasonably dark site, this telescope will reveal the ethereal glow of the Orion Nebula (M42), the glow of bright galaxies, and the outer stars of bright globular clusters such as the Hercules Cluster (M13).

Tube and Mounting: A 686mm OTA with Vixen Dovetail

The 686mm (27-inch) optical tube sits in cradle rings on a Vixen-style dovetail mounting bar, which slides into the base's dovetail saddle and is held by the saddle lock knob.

The cradle ring system offers an important point of adjustment. By slightly loosening the ring clamps, you can rotate the entire optical tube. This lets you position the focuser and eyepiece at the most comfortable viewing angle, regardless of where the telescope is pointing in the sky. To balance, slide the dovetail bar in the saddle or the tube in the rings, then retighten without overtightening.

Intuitive Pointing: The Tabletop Dobsonian Base with Altitude Tension Control

The Dobsonian base is simple to use. It provides motion in two axes: altitude (up and down) and azimuth (left and right). To aim the telescope, you simply grasp the front of the tube and push or pull it toward your target. It takes very little force, so you can make small moves to keep a target centered.

The altitude axis features an adjustable tension knob, which you adjust a little at a time: enough to keep the telescope from moving by itself, not so much that precise moves are hard. The azimuth axis is pre-set at the factory for smooth, consistent rotation. It can also be used on the ground, where you will need to kneel at the eyepiece; on a stable table the eyepiece rises to a comfortable height.

Focusing System: A 2-inch Focuser with 30x and 76x Plossl Eyepieces

The telescope is equipped with a 2-inch rack-and-pinion focuser, with a drawtube lock thumbscrew for heavy 2-inch eyepieces. Loosening the three thumbscrews on the 2-inch collar removes the 1.25-inch adapter so you can use an optional 2-inch eyepiece or Barlow.

Two eyepieces are included to get you started. The 25mm Plossl eyepiece provides a low-power magnification of 30x, for locating objects and viewing star clusters. The 10mm Plossl eyepiece offers a medium-power magnification of 76x, for the Moon and planets. The kit also includes a smartphone adapter for photos of bright targets through the eyepiece.

Finding Your Way: Aligning the 1x Red Dot Finder

The included Red Dot Finder runs on a CR2032 battery and projects a red dot onto a clear window; it does not project a beam into the sky. When you look through the finder, you see the dot superimposed on the night sky. To find an object, you just move the telescope until the red dot is pointing directly at your target.

Before your first observing session, you must align the finder with the main telescope. Do this in the evening: point the telescope at a distinct object at least a quarter of a mile away (a telephone pole, stop sign or radio tower) and center it in the 25mm eyepiece. Then, without moving the telescope, use the finder's small adjustment knobs to move the red dot until it is precisely on the same object. Once aligned, anything you place the red dot on will appear in the main eyepiece.

Optical Alignment: A 3-Step Guide to Collimating Your Mirrors

Collimation is the process of aligning the telescope's primary and secondary mirrors so they work together to produce the sharpest possible image. The optics were collimated in the factory but may have moved during shipment.

The process can be broken down into three main steps. First, look into the drawtube without an eyepiece from about a foot away and tilt the secondary mirror with its three collimation screws on the sky side of the holder until it appears round. Second, loosen the three small Phillips lock screws by no more than two turns and adjust the primary mirror with the three spring-loaded knobs at the bottom end of the tube until the center ring mark lines up with the secondary. Finally, fine-tune on a star.

Portability by Design: A 22 lb 1 oz Optical Tube

The optical tube assembly weighs 22 lbs 1 oz and is 686mm long. No base weight is given.

Go out every clear night you can for a few weeks, even for a few minutes, to build skill.

What Comes in the Box

The telescope arrives in two boxes: one with the base, one with the telescope and accessories.

In addition to the main telescope tube and Dobsonian base, the kit includes a 25mm Plossl eyepiece for wide-field views and a 10mm Plossl eyepiece for higher magnification. A red dot finder, a smartphone adapter, the 1.25-inch eyepiece adapter and an eyepiece rack that screws to the side of the base complete the list.

Your First Night Out: 5 Steps to Using the 6-inch Dobsonian

After unboxing, attach the optical tube to the base using the Vixen-style saddle. Install the red dot finder and eyepiece rack. In the evening, align the red dot finder on a distant land object. Once night falls, you are ready to observe.

Begin with the 25mm eyepiece to get a wide field of view. Use the red dot finder to aim at a bright target like the Moon or Jupiter. Once centered, use the large knobs on the focuser to achieve a sharp image. After exploring at low power, you can switch to the 10mm eyepiece for a more detailed, higher-magnification view. Remember to gently nudge the telescope to keep the object centered as it drifts across the sky.

SUN WARNING: Never attempt to observe the Sun with this device, and do not point the telescope or its finder at or near the Sun. Observing the Sun, even for a moment, will cause instant and irreversible damage to your eye or even blindness. Children should always have adult supervision while observing.