The diagram above shows how the SCT Corrector improves the off-axis spot size on a Celestron 11" SCT. Performance is similar on other size telescopes.
Focal Length
The exact focal length of the reducer/telescope combo depends slightly on where in the optical path the SCT Corrector lens is placed. Nominally it will be within a few mm of the rear threads on the telescope. Changing this distance should only affect the focal length, not the optical quality. Listed below are the nominal focal lengths for the various sizes of Celestron SCTs*. The SCT Corrector works great on standard f/10 Meade SCTs as well, we just didn't have exact data for the nominal designs of those telescopes.
| Telescope | Focal Length | Focal Ratio |
| C6 | 1220mm | f/8 |
| C8 | 1450mm | f/7.1 |
| C9.25 | 1525mm | f/6.5 |
| C11 | 1760mm | f/6.3 |
| C14 | 2365mm | f/6.7 |
* The SCT Corrector has a reduction factor of 0.63x, but the C6 and C8 are actually closer to f/11 natively, and they have a shorter backfocus compared to the larger scopes so the reduction is a bit less. The C14 is f/11 natively.
The SCT Corrector IV has a nominal image circle of 27mm, accommodating most popular CCDs and DSLRs. For larger format cameras, check out our
Because the backfocus of the SCT Corrector IV is fairly critical, for best performance Starizona makes a variety of camera adapters, and custom adapters are also easy to make for less-common camera setups.
The nominal backfocus is 90.3mm from the base of the threads on the camera side of the SCT Corrector IV. For the largest compatible cameras, this should be kept within +/-2mm, while smaller format cameras may work fine at slightly larger tolerances.
The SCT Corrector IV comes with a 35.3mm adapter with M42 Male threads. This adapter leaves you with a standard 55mm backfocus.
Telescope Adapters
The SCT Corrector IV, like the original SCT Corrector, has a 2" barrel that allows it to fit into a 2" visual back or 2" focuser. If your telescope does not have such an adapter, we recommend our rotating visual back, which allows for easily changing the camera orientation without loosening any lock screws.
Filters
The front (telescope side) of the SCT Corrector IV is threaded to accept standard 2" (48mm) filters.
Images by Kfir Simon with a Meade 12" LX200 and SBIG ST-8300M camera:
Images by Bruce Pipes with a Meade 14" LX200 and SBIG ST-8300C camera:
Images by Tyler Welch with a Celestron CGEM-800 and modified Canon 1100D camera:
Images by Gil Esquerdo with a Celestron CPC-1100 and SBIG ST-2000XM camera:
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