Celestron 91076, Instruction Manual, Page: 2 / 20

Mounting the Astrograph
The RASA 11 has a CGE dovetail mounting bar. This is compatible with mounts that accept
a CGE or Losmandy-D style dovetail. The astrograph itself weighs 35 lbs., so a mount with
a load capacity greater than that is required to ensure good performance when a camera
and any accessories are added.
Installing a Camera
Use one of the two supplied camera adapters to attach to your DSLR or astronomical
camera. The M42 adapter fits most cameras with standard T-threads. The wider M48
adapter can be used with full frame cameras with minimal vignetting. DSLR cameras
require a T-ring, sold separately, for the make and model of your camera.
Astronomical cameras have a wide range of backfocus, depending on the model and
accessories used. The included camera adapters allow 55 mm of distance from the adapter
to the imaging sensor. If your astronomical camera has a backfocus distance less than
55 mm, you will need to add a spacer to reach the correct distance.
Cameras with sensors larger than 43 mm diagonal (full frame) will require a custom adapter
to better illuminate the sensor. Refer to Celestron’s website for a drawing of camera adapter
requirements to help determine how a custom adapter should be made.
Note: Due to the steep light cone at f/2.2, camera housings can be a source of
vignetting. Despite having a large illuminated field (78% illumination at 21 mm off-axis),
vignetting can occur when the camera’s sensor is deeply recessed within its housing.
This is common with DSLR sensors, sometimes resulting in rectangular vignetting.
To Attach Your Camera:
1
. Place the knurled retaining ring over the camera adapter and loosely thread it onto
the lens group housing at the front of the RASA.
2 . Holding your camera, thread the camera body (or T-ring, if a DSLR is used) to the
camera adapter.
3
. Carefully hold the camera so the camera adapter seats flatly on the lens group housing.
4 . Finish threading the retaining ring onto the RASA. Turn until the camera adapter is
snug against the lens group housing. Do not over tighten! Camera orientation can be
adjusted later.
Caution: Over tightening the retaining ring can increase the chance of loosening the lens
assembly on the corrector, or cause the lens assembly to rotate against the corrector.
Keep the camera adapter snug against the lens group housing, but do not over tighten
the retaining ring.
Adjusting Camera Orientation
Once the camera is installed, you can rotate it by slightly loosening the retaining ring. Loosen
the ring no more than 1/8 th turn, rotate the camera as desired, and retighten the ring,
remembering not to over tighten.
Fan Operation and Optics Cool Down
It takes time for the optics of the RASA to reach thermal equilibrium with the
outside air. The greater the temperature difference between where the astrograph is
stored and the outdoors, the longer it takes to cool down.
1 Lens Group 6 Vents
2 Corrector 7 Cooling Fan
3 Optical Window Cell 8 12V DC Power Jack for Cooling Fan
4 Collimation Screws 9 Focus Knob
5 Accessory Dovetail Plate 10 Handle
Overview
3
7
4
1
2
5
6
8
9
10
Knurled
retaining
ring
Parts List
Optical Tube Assembly, M42 Camera T-adapter, M48 Wide Camera Adapter, Retaining Ring, 8 x AA Battery Pack (batteries not included) , Dust Cap
The Rowe-Ackermann Schmidt Astrograph 11 (RASA 11) is an incredibly fast (F/2.2) 11” aperture optical system that delivers a flat field without optical aberrations. It is capable of
capturing stunning deep-sky astronomical images without the difficulties presented by slower and longer focal length telescopes. The astrograph can only be used with a camera.