Celestron - 11" SCT Telescope with CGEM II Equatorial Mount - 12012
- Cutting edge optics with the 11" SCT design, an astrophotographer must have!
- Starbright XLT Coatings renders excellent quality views and images
- The Fastar application turns an f/10 system to an f/2 for very short exposure times
- Lightweight and portable enough for relatively easy transportation
- A step up from the original Celestron CGEM with new ergonomic design features
- The Celestron CGEM II Equatorial Mount has a 40 pound payload, easily capable of mounting 11" optical tubes securely for an excellent imaging setup!
- All-Star Polar alignment allows easy alignment setup by allowing the user to align with a star
- Periodic Error Correction (PEC) reduces errors and provides clean tracking, a major necessity for a successful astroimaging session
- Dual Saddle to accomodate both Vixen and Losmandy Dovetails
- USB hand controller included giving the user access to a 40,000 celestial object database
- 53" to 65" adjustable tripod legs
- 9 slew speeds at a maximum of 4.5° per second
Celestron - 11" SCT Telescope with CGEM II Equatorial Mount - 12012
Celestron - C11-A XLT - 11" SCT OTA for CGE/CGX - 91036-XLT
The Celestron C11 11" SCT Optical Tube Assembly is an excellent gem for serious astrophotgraphers who enjoy crisp images with shorter exposure times. Being lightweight with its aluminum design, it is only 24" in length with a weight of 27.5 pounds, thus still making is reasonably portable to be taken to locations for viewing or imaging with one person.
Using the Celestron Starbright XLT Coatings, high contrast views at high magnification are a walk in the park! The coatings increase contrast and light transmission; significantly improving image quality to very superior standards which is a major plus for shorter exposure astrophotography. When taking into account the durability of the Fastar system as well as the f/6.3 focal reducer, making shorter exposure times even better at 25 times shorter at f/2 than its typical f/10 optical focal ratio.
Features
- Cutting edge optics with the 11" SCT design, an astrophotographer must have!
- Starbright XLT Coatings renders excellent quality views and images
- The Fastar application turns an f/10 system to an f/2 for very short exposure times
- Lightweight and portable enough for relatively easy transportation
Starbright XLT Coatings
- Maximizing light transmission through a perfect optical path
- Starbright XLT improves color retention, contrast, sharpness, resolution, and brightness
- Starbright XLT system provides flat wavelength transmission across the entire visual spectrum. Therefore you will minimize your wavelength curvature
- Multi-layer mirror coatings with layers of aluminum, TiO2 (titanium dioxide) and SiO2 (quartz),
- Starbright XLT Multi-layer anti-reflective corrector plate coatings with layers of MgF2 (magnesium fluoride) and HfO2 (hafnium dioxide); hafnium has a wider band-pass than the commonly used titanium in lesser quality optics
- Starbright Xtra High-Transmission water white glass corrector plate limits loss of light due to absorption
Optical Coatings
Since Schmidt-Cassegrain designs use both mirrors and lenses, obtaining maximum light transmission without sacrificing quality is the key. This is where the StarBright XLT coatings come into play.
Using a technique known as "vacuum deposition", optical coatings are applied in a thin manner on the optical glass components and positioned properly relative to each other to maximize light transmission. The mirror is coated with metallic coatings that effectively increases light transmission from 4% for mirrors without coatings and 86-88% with standard coatings to a whopping 95%. This is the first step to achieving the necessary light transmission.
The second step is applying the coatings to the lens which is more sophisticated and complex process due to the fact that light is lost in both the reflection and absorption, thus resulting in further light loss. 4% is reflected back intially while more light is lost in the absorption through the glass and second lens surface. To solve this problem, Celestron has implemented dielectric materials known as A/R (anti-reflection) coatings to obtain a very low and flat reflection across the visible spectrum.
Combining these factors results in a remarkable peak transmission of 89% at 520nm and an overall average transmission of 83.5% from 400 to 750nm. The graph below demonstrates this.
How Starbright XLT is Different
The charts below show the improvement of transmission, reflectivity and corrector transmission obtained through Starbright XLT coatings verses previous coatings. It has a peak transmission of 89% vs the previous Starbright peak of 80%. In terms of reflectivity, the XLT coatings have an average peak of 93% vs previous coatings at 91%.
The Starbright XLT corrector transmission is 97.4% compared to other coatings with a lower peak.
Coating Testing
Celestron has implemented two methods to test the effectiveness of the StarBright XLT coatings.
The first method is by measuring the optical tube performanec in its entirety. This is done by comparing a beam of light passing through the optical components of the optical tube against a beam of light in air. By dividing the light ratio of the beam through the optical tube verses the beam through air, Celestron can measure the effectiveness and performance. However there are challenges to this method including but not limited to making sure the beam is constant and that light capture is effective, steady and clean and making sure the optical components are properly lined up so they don't skew the results in one way or another.
The second method is easier to execute and simply measures each component's spectrographic performance to make sure all are working properly. This method in addition to not having the setbacks of the first method, also provide greater analysis of each individual component of the optical tube, something not possible in the first method. This method also helps determine the upper limit of the telescope's upper throughput using the calculation below:
%TT = %TC x %RP x %RS
%TT is Total Telescope Throughput
%TC is Corrector Plate Transmission
%RP is Primary Mirror Reflectance
%RS is Secondary Mirror Reflectance
Corrector Plate Transmission - %TC
Using a Shimadzu UV1601 spectrophotometer, Celestron has implemented an effective way of analyzing the corrector plate transmission by using a double beam instrument with a 190 to 1100 nm spectral range with transmission usually collected within 400 to 750 nm. To avoid scratching and damaging the correct plate in the process, "witness plates" which are small samples of the corrector material are used as an alternative. This method is effective for correctors up to 8" diameter.
Primary and Secondary Reflectance - %RP, %RS
The protocol to measuring the reflectance of the primary and secondary mirrors also includes the use of "witness plates". Using 1-2" diameter polished glass substrates coated along with the primary and secondary mirrors that serve as a "stand in" for the mirrors during the testing to avoid unnecessary scratching and damage and to serve as an easy reference to measure reflectance on flat surfaces.
Celestron chose to use enhanced aluminum-coated quartz flat scaled and measured against a NIST (National Institute of Standards and Technology) specular reflectance standard. The formula to measure the reflectance is calculated by comparing it against the baseline formula below:
%RS = %RSR x %RR
%RS is Sample Reflectance Factor
%RSR is Reference Standard
%RR is Reference Standard Known Reflectance
Flat mirrors are very easy to measure using the formula above, but curved primary and or secondary mirrors on the other hand, that is a totally different story, particularly if there are no witness plates available for use. Measuring a curved mirror against a flat reflectance standard would not render accurate results. As an alternative, another method is used known as an integrating sphere. This method essentially ignores the curvature and simply measures light intensity. The downside however is this is a pricey and long process to setup. To bypass this time and cost restraint, Celestron has developed another method by creating their own reference standard for secondary and primary mirrors. By using secondary and primary mirrors that have existing coating removed and replacing it with flat witness plates scaled against the NIST standard, the data can then be applied to the curved samples. The instrument used in this process are an Ocean Optics USB2000 Spectrometer with an LS-1 Tungsten Halogen Light Source. This single beam instrument has a 0.3nm resolution with a 340-1024 nm scanning range and is equipped with a fiber optic curved surface reflectance measuring probe.
Celestron CGEM II EQ Equatorial Mount - 91523
Celestron has updated the ever popular CGEM mount. The Celestron CGEM II equatorial telescope mount includes new ergonomic design features, the All Star alignment procedure, and legendary Celestron mount performance. An instrument capacity of up to 40 pounds allows the Celestron CGEM mount to carry an 11" optical tube with ease.
The CGEM II includes extra large Altitude and Azimuth adjustment knobs so you can polar align easily, even in cold weather while wearing gloves. A dual saddle plate will accept both V and D series dovetails. Internal mount wiring keeps the exterior of your mount free from cables and prevents cable tangling or wrapping. Celestron's AllStar polar alignment procedure allows you to use any star in the night sky whether the celestial pole can be seen or not. The results are accurate polar alignment, tracking, and pointing. The Celestron CGEM II will track far beyond the meridian for uninterrupted tracking. Permanent Periodic Error Correction (PEC) will train the mount's worm gears over time to remove natural errors that occur during tracking.
Included with the Celestron CGEM II equatorial telescope mount is a USB hand controller with over 40,000 objects and 100 user-defined objects plus enhanced information on over 200 objects. The mount's tripod include height marked adjustable legs so you can quickly setup. If you were considering a Celestron AVX mount but worried it would be too lightweight, the CGEM II is a perfect fit providing a stable base for larger optical tubes and heavier imaging systems.
Features
- A step up from the original Celestron CGEM with new ergonomic design features
- The Celestron CGEM II Equatorial Mount has a 40 pound payload, easily capable of mounting 11" optical tubes securely for an excellent imaging setup!
- All-Star Polar alignment allows easy alignment setup by allowing the user to align with a star
- Periodic Error Correction (PEC) reduces errors and provides clean tracking, a major necessity for a successful astroimaging session
- Dual Saddle to accomodate both Vixen and Losmandy Dovetails
- USB hand controller included giving the user access to a 40,000 celestial object database
- 53" to 65" adjustable tripod legs
- 9 slew speeds at a maximum of 4.5° per second
UPC | 050234120128 |
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Brand | Celestron |
Free Shipping | Free Shipping Available |
Aperture | 279.4mm (11") |
Case Included | No |
Focal Length | 2800mm (110") |
Focal Ratio | f/10 |
Focal Length of Eyepiece 1 | 40mm (1.57") |
Magnification of Eyepiece 1 | 70x |
Finderscope Included | 9x50 |
Diagonal Included | 1.25" Star Diagonal |
Optical Tube Material | Aluminum |
Highest Useful Magnification | 660x |
Lowest Useful Magnification | 40x |
Limiting Stellar Magnitude | 14.7 |
Resolution - Rayleigh | 0.5 arc seconds |
Resolution - Dawes | 0.42 arc seconds |
LIght Gathering Power (Compared to the Human Eye) | 1593x |
Size of Secondary Obstruction | 95mm (3.75") |
Secondary Mirror Obstruction By Diameter | 34% |
Secondary Mirror Obstruction By Area | 12% |
Optical Coatings | Starbright XLT |
Optical Tube Length | 610mm (24") |
Optical Tube Diameter | 312.42mm (12.3") |
Optical Tube Weight | 27.5 lbs (12.4 kg) |
Included Dovetail | CGE Dovetail Bar |
Mount Load Capacity | 40 lbs (18 kg) |
Accessory Tray Included? | Yes |
Counterweights Included | 2 x 17 lbs |
Tripod Height Adjustment Range | 1346mm - 1651mm (53" – 65") |
Adjustable Legs? | No |
Tripod Leg Diameter | 50.8mm (2") Steel tripod with graduated markings on lower section |
Tripod Weight | 20 lbs (9 kg) |
Mount Head Weight | 40 lbs (18.14 kg) |
Slew Speeds | 9 slew speeds - max speed 4.5°/second |
Tracking Rates | Sidereal, Solar and Lunar |
Tracking Modes | EQ North & EQ South |
Mount Motor Drive | DC Servo Motors |
GPS | No |
Number of Auxiliary Ports | 2 Aux ports (1x Hand control port and 1x AUX Port for optional accessories) |
Includes Autoguide Port | Yes |
USB Port | Yes, input on Hand Control |
Power Requirements | 12V DC, 3.2 amps |
Computerized Hand Controller | 2 line x 18 character backlit Liquid Crystal Display, 19 LED backlit buttons, USB 2.0 port for PC connection |
Alignment Procedures | 2-Star Align, 1-Star Align, Solar System Align, Last Alignment, Quick Align |
Database | 40,000+ objects, 100 user defined programmable objects Enhanced information on over 200 objects |
Included Software | Celestron's Starry Night Special Edition Software, SkyPortal App |
Periodic Error Correction | Yes |
Total System Weight | 105.5 lbs (47.8 kg) |
Warranty | 2 Years |
In The Box |
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- CGEM II Mount Head
- Tripod
- Accessory Tray
- 2 x 17 lbs counterweight
- NexStar + Hand Control
- DC Power Cable (item # 18769)
- Hand Control Holster
- Celestron 11" SCT Optical Tube Assembly