Coma-free images from a standard SCT!
The Starizona SCT Corrector was named one of Sky & Telescope's Hot Products for 2012!
The Starizona SCT Corrector is a focal reducer and field flattener for standard Schmidt-Cassegrain telescopes. It converts the telescope from f/10 to f/7.5, resulting in a wider field and faster imaging. f/7.5 is nearly 1.8 times faster than f/10!
The field is optimized for a 35mm image circle. Spot sizes are up to 5 times smaller than the native telescope, and coma is completely eliminated. The result is much sharper stars across a large, flat field of view. A standard 2" mounting allows a variety of telescope attachment options.
The SCT Corrector has 90mm (3.5") of mechanical backfocus, accommodating a large variety of cameras and filter wheels. Spacers are required to set the exact backfocus distance and are available separately for a variety of cameras (see below).
- 0.75x Focal Reduction
- 35mm Optimized Image Circle
- 2" Diameter
- 90mm Backfocus
- Threaded for 2" (48mm) Filters
- Fully Multi-Coated Optics
- Made in USA
Example Specifications (11" SCT)
- Focal Ratio: f/7.5
- Focal Length: 2100mm
- Corrected Field: 56 arcminutes
RMS Spot Size Comparison (11" SCT)
Above: A plot of the spot size across the field for an 11" SCT without the corrector (black) and with the corrector (blue). On-axis performance is equal, but even slightly off-axis, the spot size of an uncorrected SCT grows rapidly due to field curvature and coma. The corrected telescope has a very flat field with small spots all the way across the image.
Above: Comparison of the upper left corner of images from a Celestron 11" SCT and Canon EOS 7D camera. Each image is a 100% crop of the upper left corner of the frame. The pictures were taken through the same scope within minutes of each other using 5-second exposures at ISO1600. Compare the elongated comatic stars in the left image at f/10 to the perfectly round, smaller stars in the right image with the SCT Corrector in place.
Spot Diagram Comparison
Shown below are spot diagrams for a Celestron 11" SCT at the native f/10 focal ratio, with a standard Celestron f/6.3 focal reducer, and with the Starizona f/7.5 SCT Corrector.
Available Camera Adapters
- Canon EOS
- QSI 500/600
- SBIG ST/STF/STT
- Starlight Xpress
- Custom adapters available--please contact us
Dimensions (without camera adapter)
- Diameter: 2.00" (50.8mm)
- Length: 1.85" (47mm) + 0.20" (5mm) thread
- Weight: 7.7 oz (218g)
Note that since the SCT Corrector is designed to correct the coma inherent in standard Schmidt-Cassegrain telescopes, it will not work properly with Celestron EdgeHD or Meade ACF optical systems.
View the instruction manual for this product
Using the Starizona SCT Corrector with an Off-Axis Guider
The distance from the SCT Corrector lens to the focal plane of the camera is critical to achieving the best image quality. Adapters are available for a variety of cameras which places the camera at the correct distance from the lens. If an off-axis guider (OAG) is added, the thickness of the OAG must be subtracted from the length of the camera adapter. However, it is also necessary that the distance from the pick-off prism in the OAG to the guide camera be the same as the distance to the main camera, in order that both can be focused at the same time. Click diagram below.
Keeping the main camera and guide camera at the same distance from the OAG prism usually requires a spacer between the OAG and main camera. When this setup is used with the SCT Corrector, to total length of the OAG plus any camera spacer must be subtracted from the adapter that is needed. Ultimately, two or three adapters will be needed to use an OAG with the SCT Corrector. The most popular off-axis guider we sell is the Starlight Xpress SX-OAG. This OAG has a thin profile and is well built.
The usual configuration would be to get the OAG with a female T-thread on the telescope side and a male T-thread on the camera side. Then you just need the proper length T-to-T-thread spacer between the OAG and camera to set the distance between the OAG prism and main camera; and the proper length SCT Corrector-to-T-thread adapter between the OAG and SCT Corrector to set the distance from the lens to the camera. The SX-OAG has C-threads on the guide camera port, which fit the popular Lodestar and Superstar autoguiders. If you use a guide camera with T-threads, such as the Orion Starshoot Autoguider, you will also need a C-to-T-thread adapter. Click diagram below.
We have various adapters in stock, and can custom make any other styles that might be needed. Please contact us for details.
Atik Camera Adapter
Canon EOS Adapter
Celestron Nightscape Adapter
QHY Camera Adapter
QSI Camera Adapter
SBIG Camera Adapter
Starlight Xpress Camera Adapter