Sharpstar SCA310 f/3.8 Aspherical Cassegrain Astrograph

310mm f/3.8 Aspherical Optics with 95% Reflectivity

At the core of the SCA310 is a 310mm parabolic (aspherical) primary mirror, precisely figured to eliminate spherical aberration for sharp, round star points. Paired with a 184mm spherical secondary mirror made of fused silica for thermal stability, this Cassegrain design delivers a 1178mm focal length within a remarkably short optical tube. Both mirrors feature enhanced aluminum coatings that ensure reflectivity of over 95%, maximizing light transmission to your camera sensor.

The fast f/3.8 focal ratio dramatically reduces required exposure times, allowing you to capture more data on faint targets like the nebulae in Cygnus or distant galaxy clusters in a single night. This speed is a significant advantage for imagers working from locations with limited clear sky time or for those pursuing advanced multi-filter narrowband projects.

A 55mm Corrected Image Circle for Medium Format

The SCA310 integrates a 3-inch triplet corrector at the rear of the optical tube. This three-element design, which includes one ED (Extra-low Dispersion) glass element, is engineered to correct for field curvature and coma, ensuring sharp stars from the center to the edge of the frame.

The result is a 55mm image circle that SharpStar specially optimizes for medium format and that fully covers full-frame sensors, with nearly 100% illumination and a flat image field even on full-frame cameras. With a full-frame sensor (36 x 24mm), the 1178mm focal length gives a field of about 1.75° x 1.17°, enough to frame M81 and M82 together or the Orion Nebula (M42) with M43.

721mm Carbon Fiber Tube with 3 Cooling Fans

The SCA310's optical assembly is housed in a carbon fiber tube with an outer diameter of 378mm. This material provides exceptional stiffness and a low coefficient of thermal expansion, ensuring focus remains stable as ambient temperatures drop during an imaging session. This stability is critical for maintaining sharp stars over many hours of automated data acquisition.

To achieve peak optical performance quickly, three cooling fans are integrated into the rear cell behind the primary mirror. By activating these fans before your session begins, you can rapidly bring the 310mm primary to ambient temperature, minimizing internal tube currents and improving image quality from the start of the night. A switch on the rear panel turns the fans on and off and adjusts their speed.

3.5-inch Focuser, 360° Rotator, and M68/M54/M48 Adapters

The SCA310 is equipped with a high-rigidity 3.5-inch rack-and-pinion focuser with 28mm of travel. It features a 1:10 dual-speed knob for precise adjustments, and even when loaded with multiple accessories it stays stable and smooth, without slippage. A 360° rotator is mounted at the front of the focuser, letting you set the camera angle to frame your target and helping prevent cable wrap. The focuser and rotator ship locked: loosen their locking screws before first use to avoid damage.

The rear of the focuser includes M68, M54, and M48 thread-on adapters, providing direct, secure connections for a wide range of cameras and accessories. The optical design supports a back focus range of 38-66mm, and no additional back focus calculations are needed: simply attach your camera with the appropriate adapter to begin imaging.

• 2-inch Filter Thread: The included M48 adapter features an internal M48x0.75 thread for direct mounting of 2-inch filters.
• Rear Connection Distance: The supported range is 38-66mm.

A 23.5kg OTA with 405mm Losmandy Plate

The SCA310 optical tube has a gross weight of 23.5kg. This substantial mass calls for a high-capacity equatorial mount for stable tracking in long-exposure astrophotography. Choose a mount whose rated instrument capacity comfortably exceeds the OTA's 23.5kg plus the weight of your camera, guiding setup and accessories.

For secure mounting, a fully CNC-machined, 405mm long Losmandy-style dovetail plate is attached to the bottom of the tube. A hollowed top handle bar provides a secure grip for handling the instrument and includes multiple mounting holes for expansion accessories.

User-Adjustable Primary and Secondary Mirrors

The SCA310 is collimated at the factory, but transport impacts or cleaning can shift the optical axis, so user adjustment is provided for. The secondary mirror uses a three-point push-pull screw design, while the primary mirror is adjusted via three sets of screws at the base of the optical tube. The system also allows for fine adjustment of the primary-secondary spacing.

The manual provides a detailed procedure for both mechanical collimation using a tool like an OCAL and on-sky optical collimation via a star test. This lets you keep the optics aligned so the instrument can perform to its rated resolution of 0.37 arcseconds.

SCA310 vs. 12" Newtonian Astrographs: The Cassegrain Advantage

A 12-inch (approx. 300mm) f/4 Newtonian offers similar aperture and speed, but the SCA310's Cassegrain design provides key advantages for dedicated imagers. The most significant is compactness: at just 721mm long, the SCA310 is over 400mm shorter than a typical 12" f/4 Newtonian OTA. This reduces strain on the mount, makes balancing easier, and simplifies transport and storage.

The SCA310's corrector is also an integrated part of the optical design, so you do not need to buy and space a separate coma corrector. Its closed carbon fiber tube also shields the light path from stray light, unlike an open-truss design.