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Starizona SCT Corrector IV - 0.63x Reducer / Coma Corrector
The Starizona SCT Corrector IV transforms a standard f/10 Schmidt-Cassegrain into a corrected, wide-field astrograph by reducing the focal ratio by 0.63x and making the system 2.5x faster. Its 5-element optical design incorporates ED glass to correct off-axis coma across a 27 mm image circle. By converting a C11 to f/6.3 or a C8 to f/7.1, this corrector dramatically shortens exposure times while capturing a much wider field of view.
A 0.63x Reducer for a 2.5x Faster System
By reducing your telescope's focal length by a factor of 0.63x, the SCT Corrector IV makes your imaging setup 2.5x faster than its native f/10 configuration. This speed increase means you can capture the same amount of signal in less than half the time. For example, a Celestron C11 becomes a 1760 mm f/6.3 instrument, and a C9.25 operates at 1525 mm f/6.5.
A 5-Element ED Design for Coma-Free Fields
The Starizona SCT Corrector IV is both a focal reducer and a coma corrector. Its 5-element optical path, which includes extra-low dispersion (ED) glass, is specifically engineered to counteract the inherent off-axis coma of SCT optical systems. Starizona's spot diagram for a Celestron 11" SCT shows much smaller off-axis star images than the native telescope, and performance is similar on other sizes.
Achieving 90.3mm Backfocus for Optimal Correction
To deliver its specified correction, the SCT Corrector IV requires a precise mechanical backfocus of 90.3 mm, measured from the base of its M42 camera-side threads to your sensor plane. For the best results, this distance must be maintained within a tolerance of +/-2 mm. The corrector includes a 35.3 mm M42 spacer which, when attached, leaves a standard 55 mm backfocus, suitable for a DSLR with a T-ring or ZWO cooled cameras with their stock adapters. The telescope side features a 2" barrel with 48 mm filter threads, allowing it to slide into any standard 2" focuser or visual back.
SCT Corrector IV vs. the Original SCT Corrector
The SCT Corrector IV is the current version of Starizona's SCT Corrector, combining a 0.63x reducer and a coma corrector in one 2" barrel unit.
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Speed: It is 1.4x faster than the original f/7.5 SCT Corrector design.
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Optics: A 5-element design with extra-low dispersion (ED) glass and fully multi-coated optics.
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Larger Sensors: For full-frame cameras on a C11 or C14, Starizona offers the SCT Corrector LF with a 42 mm image circle.
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What does the Starizona SCT Corrector IV do?
It reduces the focal ratio of a standard SCT by 0.63x, making the system 2.5x faster than the native f/10, and corrects off-axis coma. Its 5-element design uses extra-low dispersion (ED) glass and covers a 27 mm image circle.
How do I get the correct 90.3 mm spacing for the SCT Corrector IV?
The 90.3 mm distance is measured from the shoulder of the M42 T-threads on the corrector to your camera's sensor. The corrector includes a 35.3 mm spacer adapter. When this is attached, you are left with a standard 55 mm backfocus requirement, which is common for DSLRs with a T-ring or ZWO cooled cameras with their stock adapters. You may need additional M42 spacers to achieve the correct distance for your specific imaging train.
Will the Starizona SCT Corrector IV work with my 8" f/10 Meade SCT?
Yes. Starizona states it works great on standard f/10 Meade SCTs, although it publishes nominal focal lengths only for Celestron models (for example 1450 mm at f/7.1 on a C8).
What focal length and focal ratio does the SCT Corrector IV give on a C11?
On a Celestron C11 it reduces the native 2800 mm focal length to a nominal 1760 mm at f/6.3, for a wider field of view and a system 2.5x faster than f/10. The exact focal length depends slightly on where the corrector sits in the optical path.
Which cameras does the 27 mm image circle of the SCT Corrector IV cover?
The 27 mm image circle accommodates most popular astronomy cameras and DSLRs. For the largest compatible cameras, keep the 90.3 mm backfocus within +/-2 mm. For full-frame sensors on a C11 or C14, Starizona offers the SCT Corrector LF.
Can I use filters with the Starizona SCT Corrector IV?
Yes. The front (telescope side) of the corrector is threaded for standard 2" (48 mm) filters.
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| Optical Design |
5 elements with extra-low dispersion (ED) glass |
| Reduction Factor |
0.63x |
| Imaging Speed |
2.5x faster than native f/10 |
| Corrected Image Circle |
27 mm |
| Mechanical Backfocus |
90.3 mm (3.56") from M42 thread shoulder |
| Backfocus w/ Adapter |
55 mm (with included 35.3 mm spacer) |
| Telescope Connection |
2" barrel |
| Camera Connection |
M42 x 0.75 mm (T-thread) |
| Filter Threads |
48 mm (for 2" filters) on telescope side |
| Resulting f/ratio (C6) |
f/8 (1220 mm) |
| Resulting f/ratio (C8) |
f/7.1 (1450 mm) |
| Resulting f/ratio (C9.25) |
f/6.5 (1525 mm) |
| Resulting f/ratio (C11) |
f/6.3 (1760 mm) |
| Resulting f/ratio (C14) |
f/6.7 (2365 mm) |
| Compatible Telescopes |
Standard f/10 Celestron and Meade SCTs |
| Coatings |
Fully multi-coated optics |
| Housing |
Black anodized, machined aluminum |
| Barrel Diameter |
2" |
| Length |
2.5" (excluding threads) |
| Weight |
270 g (0.6 lb) |
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SCT Corrector IV 0.63x Reducer / Coma Corrector
× 1
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35.3 mm Spacer Adapter (M42)
× 1
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Starizona Warranty
