“I don’t get it. What do you look through?”
This might be the most common question people ask when you
unpack your new Celestron Rowe-Ackermann Schmidt Astrograph (RASA). It’s not
only missing something that comes with virtually every telescope ever produced .
. . an eyepiece . . . it doesn’t even have a place to put an eyepiece. That’s
because the 620mm focal length f/2.22 Celestron 11” RASA is strictly a deep
space imaging scope and cannot be used visually.
But what an imaging scope! It has a huge 70mm image circle
that can handle full frame DSLRs and the largest sensor size CCD cameras with
minimal vignetting. It provides a proven Schmidt corrector optical system with a
built-in 4-element rare earth corrector lens that keeps the images free of
coma, field curvature, and false color. The optical quality and spot size across
the entire image circle are unprecedented for an astrograph in this price range
– or even that of a much more expensive instrument.
Its fast, wide field, f/2.22 optics give you two huge
advantages over traditional f/10 catadioptric imaging scopes (even those using
an optional f/6.3 or f/7 focal reducer). Those advantages? Better apparent
tracking due to the image scale, plus shorter exposure times due to the speed of
the optics. That means you can create better-looking deep space images in a
fraction of the time it used to take, even without using an autoguider.
The Celestron RASA concept was to
modernize the Celestron Schmidt camera, an instrument that had a loyal
following, as its very fast focal ratio allowed amateur astrophotographers to
produce wide field deep space images in the 1970s. Schmidt cameras could produce
great images, but they wre and imaging scope only a really hard-core astrophotographer could love.
Those Schmidt cameras used a single
frame of 35mm film, cut from a roll of film. You flexed the chip of film in
total darkness (being careful not to touch the emulsion side) to fit snugly into
a curved holder that matched the camera’s curved focal plane, then loaded it
into the camera by feel inside a black cloth bag to avoid image-spoiling stray
light. You manually guided your scope during the entire exposure, keeping your
eye glued to the crosshairs of an illuminated reticle eyepiece so your stars
wouldn’t turn into elongated squiggles. Finally, after a sometimes multiple hour
single exposure, you tediously processed the small chip of film in your own
darkroom before you could even begin to see if you had
captured a usable image.
The 11" f/2.2 Rowe-Ackermann Schmidt Astrograph Telescope from Celestron is specifically designed for astrophotography and astroimaging with a large 11" aperture and fast f/2.2 focal ratio. The OTA is being offered by itself without a mount, and comes with a Celestron CGEM-style dovetail plate for use on compatible mounts and tripods. Using the improved StarBright XLT multi-coating system, light transmission is increased throughout the entire optical path with anti-reflection multicoated lenses, highly reflective multicoated mirrors, and 4-element rare-earth glass.
A 70mm imaging circle is made to cover today's large DSLR and CCD imaging sensors to capture full-frame shots. Its fast focal ratio reduces exposure times without sacrificing image quality, and gives the user more time for multiple shots of the same object for layering or with different filters, or to change subjects completely. A custom-designed 10:1 linear brass focuser enables very precise focusing to clearly resolve topographic details on the Moon, virtually remove comas and corona from distant stars, and reveal details of most other celestial objects in between. Since this OTA is designed as an imaging scope, a 42mm T-thread camera adapter and 48mm camera adapter are provided. Other adapters are available if required.
- StarBright XLT Coating System
- Multi-layer mirror coatings made from layers of aluminum, SiO2 (quartz), TiO2 (titanium dioxide), and Si02 (silicon dioxide)
- Reflectivity is flat across the light spectrum, for both astrophotography/astroimaging and visual observation
- Multi-layer anti-reflective coatings made from layers of MgF2 (magnesium fluoride) and HfO2 (hafnium dioxide)
- High-transmission water white glass corrector lens with 97.4% light transmission
- Use and Handling
- Linear brass focuser-bearing reduces image shift
- Dual-speed 10:1 FeatherTouch micro focus knob provides precise focusing
- Heavy duty CGEM dovetail plate
- Construction Details
11" (27.9 cm)
2.2" (5.5 cm), from front lens assembly
Eyepiece Barrel Diameter
CGEM dovetail plate
12 VDC for fan operation
33" (83.8 cm)
35 lb (15.9 kg)
Celestron 11" f/2.2 Rowe-Ackermann Schmidt Astrograph Telescope (OTA only) 42mm T-Adapter 48mm Camera Adapter Limited Two-Year Warranty