Celestron 11" RASA V2 OTA - CGE Dovetail

The f/2.2 Rowe-Ackermann Schmidt Design: Capturing Data Faster

The core of the RASA 11 V2 is its f/2.2 focal ratio. It allows shorter exposure times than traditional f/10 astroimaging without sacrificing resolution, and the short 620mm focal length also lessens equatorial tracking demands. The design builds on Celestron's Schmidt Cameras, which let astrophotographers make much shorter exposures on film in the 1970s.

This design places a 4-element rare-earth glass lens group at the front of the telescope, where the camera mounts. Engineered for a wide 400-700 nm wavelength range and finished with StarBright XLT coatings, the optical system delivers images free of false color, coma, and field curvature. Celestron adds that the design provides minimal vignetting.

11" Aperture and 620mm Focal Length: A 43.3mm Image Circle

Designed for modern astronomy cameras, the RASA 11 V2 produces a 43.3mm optimized image circle, to capture pinpoint stars on large imaging chips, and optical performance is still excellent for sensors with diagonals up to 52mm. Combined with the 620mm focal length, it is suitable for wide-field imaging, huge mosaics of the night sky, surveying and even comet hunting.

• RMS Spot Size: At less than 4.4 μm across the field of view.
• Off-Axis Illumination: The field remains evenly illuminated, maintaining 83% brightness at 21mm off-axis.
• Central Obstruction: The 114mm central obstruction, at 41% of the aperture diameter,.

Camera Integration: 55mm Back Focus with M42 & M48 Adapters

The two included camera adapters allow 55mm of distance from the adapter to the imaging sensor. The M42 adapter fits most cameras with standard T-threads, and the wider M48 adapter can be used with full-frame cameras with minimal vignetting. DSLRs need a T-ring for the camera make (sold separately). If your astronomical camera has less than 55mm of back focus, add a spacer to reach the correct distance; cameras with sensors larger than 43mm diagonal need a custom adapter, and Celestron's website has a drawing of the camera adapter requirements.

The camera attaches to the front of the astrograph via a knurled retaining ring that secures the adapter to the main lens group housing. This system allows for easy rotation of the camera to frame your target perfectly without removing it from the optical tube.

Filter Integration: Removing the Optical Window for Peak Performance

To maintain the highest optical performance, the RASA 11 V2 is designed to have its integrated optical window removed when a filter is placed in the light path. Because the f/2.2 system is so fast, any additional flat glass (like a filter or a camera's own sensor window) can affect image quality. Remove the window whenever a filter is used, and consider it if your camera has its own optical window.

This feature allows you to use your preferred imaging filters without compromising the optical correction. Celestron also offers a Light Pollution Imaging Filter designed specifically for the RASA 11 that mounts in place of the optical window, which can help with longer sub-exposures from light-polluted skies.

The Ultra-Stable Focus System (USFS): Minimizing Image Shift

A common challenge in moving-mirror telescopes is focus shift and mirror flop. The RASA 11 V2 addresses this with the Ultra-Stable Focus System (USFS), a redesigned focuser built around a precision linear ball bearing. The bearing minimizes focus shift (unwanted lateral motion of the primary mirror during focusing, which shifts the image) and mirror flop (movement of the primary mirror as the telescope points to different positions in the sky).

The USFS is compatible with the optional Celestron Focus Motor (#94155-A), which lets you focus from the same computer that controls the camera; the manual notes that third-party software can even autofocus with it.

Thermal Management: The 12V DC MagLev Cooling Fan

Reaching thermal equilibrium is essential for sharp images, and the RASA 11 V2 accelerates this process with an integrated cooling system. A 12V DC MagLev fan, located in the rear cell, pulls ambient air through the optical tube and past the primary mirror. This active ventilation significantly reduces cooldown time, allowing you to start imaging sooner.

The fan is powered by an included battery pack that holds 8 AA batteries (not included) or any external 12V DC power supply providing at least 100mA. The vents are filtered to prevent dust from entering the optical tube, ensuring the internal optics remain clean while the system stabilizes.

Precise Alignment: Collimation and Camera Rotation

While the RASA 11 V2 arrives factory-aligned, minor adjustments may be needed after transport. Collimation is performed by adjusting the tilt of the front lens assembly using a simple push-pull system of three screw pairs. This process is done with the camera installed: defocus a star by about one turn of the focus knob and adjust one pair of screws (3mm socket head and 2mm set screw) at a time until the pattern is concentric.

Camera orientation is equally straightforward. By slightly loosening the main retaining ring (no more than 1/8th of a turn), you can rotate the camera to achieve the ideal framing for your target. Once positioned, you simply retighten the ring to secure the camera in place.

Mounting the 43 lb RASA 11 V2: CGE Dovetail System

The RASA 11 V2 optical tube weighs 43 lbs (19.5 kg) and measures 33" long. It comes equipped with a CGE-style dovetail bar, which is compatible with mounts that accept CGE or Losmandy-D plates. A mount with a load capacity greater than the astrograph's weight is required for good performance once a camera and accessories are added.

In addition to the primary mounting bar, a second CGE-style dovetail is included on the top of the optical tube. It provides a connection for optional accessories like a guidescope.