Putting the camera at prime focus makes the RASA an f/2 telescope
The classic Schmidt camera used a curved photographic plate at prime focus. Celestron's Rowe-Ackermann design, developed by Mark Ackermann, Dave Rowe and John Hall, adds a multi-element lens group in front of the focal plane so the field is flat for a digital sensor. With no secondary mirror, the light reaches focus in one reflection, and the focal ratio drops to f/2.
Speed scales with the square of the focal ratio: at f/2 the RASA collects as much light per pixel in 1 minute as an f/8 telescope does in 16. The costs are tight focus tolerance, a camera and its cable that sit in the light path, and a need for a small, cool-running camera.
Celestron makes every RASA, and stock was short in late 2026
| Model | Aperture | Focal length | Price |
|---|---|---|---|
| RASA 6 | 150 mm | not listed | $1,699, tube only |
| RASA 8 | 203 mm | 400 mm (f/2) | $2,199, tube only |
| RASA 11 V2 | 279 mm | 620 mm (f/2.2) | $4,499, tube only |
| RASA 36 V2 | 356 mm | 790 mm (f/2.2) | $14,999, tube only |
| Origin Mark II (smart telescope) | 152 mm | f/2.2, built-in camera | $4,299 |
Prices are US list prices checked in November 2026. Special-order instruments are quoted by the dealer.
Celestron's own store listed every RASA as out of stock in November 2026. Celestron is a US brand owned by Synta, and the tubes are made in China. The Origin is a 6-inch RASA with its camera, mount and computer built in, controlled from a phone like the smaller smart telescopes.
The RASA 11 frames the Orion Nebula, the Triangulum Galaxy and the Eagle Nebula whole
On an APS-C camera with the Sony IMX571 sensor (23.5 x 15.7 mm, 3.76-micron pixels), a RASA 11 at 620 mm gives a field of 2.17 x 1.45 degrees at 1.25 arcseconds per pixel. 103 of the 110 Messier objects fit in the frame, and 22 of them fill at least a quarter of its short side, among them M33 (Triangulum Galaxy), M16 (Eagle Nebula), M42 (Orion Nebula) and M22 (Sagittarius Cluster).
The RASA 8 illuminates an image circle of about 22 mm, so it suits small and 1-inch sensors such as the IMX533 and IMX585; the RASA 11 and RASA 36 cover APS-C and larger.
Most backyard skies blur stars to 2 to 3 arcseconds. Image scales below about 0.7 arcseconds per pixel record no extra detail, so cameras on long focal lengths are usually binned 2x2.
A RASA cannot be used visually at all
The focus lies inside the tube, where only a camera fits. Buy one only for imaging, and only with a mount that carries it steadily. For an 8-inch telescope that does both, look at a Schmidt-Cassegrain; Celestron's EdgeHD and the Starizona Hyperstar adapter let some of them image at f/2 as well.