Celestron 36cm (14″) Rowe-Ackermann Schmidt Astrograph (RASA) f/2.2 Optical Tube Assembly (OTA Only)


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RASA White Paper

This larger version of the original Celestron 11″ RASA was developed for the field of Space Situational Awareness (SSA). SSA is a project dedicated to detecting and mapping space junk in orbit.

In 2015, SSA professionals discovered the smaller 11″ RASA is an ideal instrument for this application. With its fast focal ratio and wide field of view it can detect even small pieces of space junk traveling at extraordinarily high speeds. There are now dozens of RASA telescopes in use around the world every night scanning the skies to protect satellites, at a fraction of the cost of other systems!

Celestron’s team collaborated with SSA experts to develop an even better telescope to meet this important need. The result is the 14″ RASA 36 which can detect individual pieces of debris measuring less than 1 meter!

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First introduced in 2014, the Celestron Rowe-Ackermann Schmidt Astrographic (RASA) telescope has an 14″ aperture and a fast f/2.2 system. This very popular instrument offers astrophotographers a way of obtaining wide-field imaging in a fraction of the time, even without the use of an autoguider.

Celestron has now announced a bigger brother to the 11″ model – the RASA 36 – a 14″/36cm aperture version. Designed and introduced as cost-effective optical system for space surveillance, Space Situational Awareness (SSA;) advanced wide field astroimaging, and other scientific applications, it offers unprecedented value in aperture, speed, field of view, and optical performance. The RASA design has a convenient external prime-focus image capture location with a flat focal plane, providing small spot sizes to the edge of a wide field. The result is images free of optical defects like field curvature, off-axis coma, and astigmatism.

The 36 cm aperture version is the largest RASA that Celestron manufactures. This astrograph is the biggest and fastest (f/2.2) optical instrument of its kind available “off-the-shelf.” Unlike most telescopes, which only focus visible light (400-700 nm), the RASA 36 cm focuses an extended spectral range (400-900 nm), allowing a brighter signal to be detected by a camera sensor. The RASA 36 cm also features a redesigned focus system, which ensures easy and stable focusing.

The RASA 36 cm’s ample back-focus distance (77.5 mm) accommodates a wide variety of imaging sensors. A custom camera adaptor can be added for a field of view up to 4.4 degrees.

About SSA

Since the USSR launched the Sputnik satellite in 1957, we have relied on earth-orbiting satellites to play an ever-increasing role in global communications. Today, thousands of satellites and hundreds of thousands of pieces of “space junk” now orbit our planet Earth.

It is a sobering thought that just one day, one stray piece of space junk could damage crucial satellites and disrupt communications on a worldwide scale. The field of Space Situational Awareness (SSA) is devoted to monitoring the space environment and protecting our satellites from debris by detecting and mapping space junk in orbit. In no small way, SSA makes our globally connected way of life possible.

In 2015, SSA professionals announced that Celestron’s original 11″ Rowe-Ackermann Schmidt Astrograph (RASA) is an ideal instrument for SSA applications. Its fast focal ratio and wide field of view allow it to detect even small pieces of space junk traveling at extraordinarily high rates of speed. Currently, there are dozens of RASA telescopes in use around the world every night scanning the skies to protect our artificial satellites at a fraction of the cost of other systems.

Celestron’s team approached SSA experts to collaborate on an even better telescope to meet this important need. The result is the RASA 36. Assembled at our Torrance, California, headquarters from start to finish, this ultra-precise optical instrument can detect individual pieces of debris measuring less than 1 metre in size.

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  • Celestron 36cm 14″ f/2.2 Rowe-Ackermann Schmidt Astrograph (OTA Only)
  • 48mm T-Adapter
  • Fan Battery Pack
  • Limited 2-Year Warranty
Optical Design Rowe-Ackermann Schmidt
Aperture 14.0″ / 355.6mm
Focal Length 790mm
Focal Ratio f/2.2
Back Focus With included camera adapter: 2.16″ / 55.0mm
From top of threaded collar: 3.05″ / 77.5mm
Eyepiece Barrel Diameter N/A
Diagonal None
Finderscope None
Tripod None
Mount Type Losmandy-D/CGE dovetail plate
Power Requirement 8 x AA batteries
12VDC, 100mA power adapter
Dimensions Length: 42.5″ / 1079.5mm
Diameter: 16.0″ / 106.4mm
Weight 75.0.0 lb / 34.0 kg

We recommend Astrodon’s 5nm narrowbands for imaging with the RASA or any telescope faster than f/2.8
(More info below)

Using Astrodon Filters at Focal Ratios below f/3.5

 Astrodon officially puts the recommend focal ratio limit at f/3.5. That said, it is a conservative limit and other filter manufacturers specify their limit much more optimistically. But we (Astrodon) maintain that filter performance will be somewhat degraded at focal ratios below f/3.5. Let’s explore the consequences of “pushing the limits” and using Astrodon filters (or any brand of filters) at focal lengths below f/3.5. Many imagers will be willing to make these tradeoffs if they understand the pros and cons.

Blue Shift

Anything between f/2.8 and f/3.6 will result in a 0.8nm blue shift, which will easily remain within the bandpass width of a 3nm bandwidth filter. Also, the eye won’t be able to pick up a shift this small. At some point, the blue shift will be large enough to start to move out of the bandpass of the filter. So, for imaging at focal ratios at or below f/2.8, we recommend Astrodon’s 5nm bandpass filters.

Halo Size and Focal Ratio

The short answer is that filter thickness and coating quality are significant factors in determining halo size, but there are limits as to what the filter can do. Different setups are going to perform differently because the (1) distance between sensor and filter and (2) focal ratio are both important variables.

The Halo Formula is:

Distance Traveled = Halo Size X Focal Ratio

Solving for Halo Size:

Halo Size = Distance Traveled divided by focal ratio
Where Distance Traveled:

Is the filter thickness divided by the refractive index (assume 1.5 as a ballpark refractive index but this is where higher quality filters come in) plus the distance from the filter to the sensor.

Astrodon filters are thin (3mm) and the coatings are of high quality. This is a critical factor in determining the final halo size. So Astrodon’s are famous for their small halo size; they perform much better than most other filters, but there are limits to what any filter can do. The Distance Traveled in your system is an important factor as well. Obviously, closer is better. But focal ratio is another critical factor. That “divided by the focal ratio” is inescapable.

Let’s compare halo size in an f/8 system and an f/2 system. If all the parameters in the f/8 and the f/2 scope are otherwise equal…

Divide the Distance Traveled by 8 (with the f/8 scope) and you get a pretty small halo. Divide the Distance Traveled by 2 (with the f/2 scope) and the halo is going to be 4 times bigger.

There is no escaping the math. You are going to have some halo even with Astrodon filters if the distance between filter and sensor is large and/or the focal ratio is fast.