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Sporting a distinctive large aperture and deep light bucket, the Explore Scientific FirstLight 203mm f/6 Alt-Az Dobsonian Telescope gives users powerful performance at a reasonable price. Its large parabolic primary and smaller secondary mirrors are made from low-expansion glass to eliminate distortion across the entire field of view, especially at the edges, while allowing sharp resolution of star clusters and nebulae that smaller apertures cannot achieve.
The fast f/6 focal ratio and hexagonal rack-and-pinion focuser make this an ideal choice for imaging, by enabling shorter exposure times with the ability to achieve tack-sharp focusing with the strength to handle large imaging rigs and eyepieces. This 2.5" focuser is designed to eliminate vignetting when using large wide-field eyepieces when observing, and when using large imaging sensors for astrophotography. Reducer adapters are included allowing the use of both 1.25" and larger 2" eyepieces and accessories.
The heavy base provides a rock-steady platform with very low vibrations. This alt-az rocker mount features Teflon pads on the ground plate, and large altitude wheels for smooth and easy movement along both axes with little vibration. Dual mounting rings allow the OTA to be precisely balanced for even smoother movement, and the altitude wheels can be removed and replaced with a Losmandy-style dovetail plate so the OTA can be used with EQ and GoTo mounts mounted on large tripods or piers.
- 203mm (8") aperture
- f/6 focal ratio
- 1218mm focal length
- Optical design: Dobsonian-variant of a Newtonian reflector
- Low-expansion H-PZ33 glass primary mirror
- 57mm low thermal-expansion Borosilicate glass secondary mirror resists expansion to limit aberrations
- Resolution: 0.6 arcsec
- Alt-az rocker design
- Large aluminum altitude wheels allow for smooth movement and tracking with reduced vibration
- Teflon pads on ground plate enable smooth 360° rotation
- Adjustable mounting rings enable precision balancing when using lighter or heavier accessories for smoother motion
- Mounting rings allow the altitude wheels to be removed and replaced with a Losmandy-style dovetail for attachment to an EQ, alt-az, or GoTo mount head for tripod/pier use
- Large 2.5" hexagonal rack-and-pinion design
- Provides strength and rigidity to handle heavy eyepieces and imaging rigs with little backlash, tilt, or shifting
- Large drawtube prevents vignetting with wide-field eyepieces during observation, or when using large imaging sensors for astrophotography
- Includes 2" and 1.25" eyepiece adapters to allow use of a variety of eyepieces and accessories
- Super Plössl eyepiece:
- 1.25" diameter barrel
- 25mm yields 49x power
- Finderscope:
- Red-dot finder
- Wide-field for fast subject acquisition and easy star hopping