Celestron Reducer/Corrector f/6.3 for Schmidt-Cassegrain Telescopes

Product overview

The Celestron Reducer/Corrector (Item #94175) is a threaded optical accessory that turns a Celestron Schmidt-Cassegrain telescope (SCT) into a dual-purpose instrument. Left off, the telescope keeps its long native focal length for high-magnification views of the Moon, planets and double stars. Threaded on, it shortens the focal length and focal ratio by about 37%, giving a faster, wider-field telescope suited to galaxies, nebulae, star clusters and astrophotography.

In practical terms, an f/10 SCT becomes f/6.3, and an f/11 SCT (C14) becomes f/7. The same eyepiece delivers lower magnification and a wider true field, while cameras capture a larger area of sky and need noticeably shorter exposures to reach the same signal.

Key features

• Two telescopes in one: switch between a long-focus planetary scope and a fast deep-sky scope in seconds.
• 37% focal length reduction: f/10 → f/6.3; f/11 → f/7.
• Field correction: reduces (but does not fully remove) the natural field curvature of SCT optics, giving flatter, sharper star images toward the edge of the field.
• Fully multi-coated optics: high light transmission with near full-field illumination.
• Precision housing: black-anodised machined aluminium body with blackened, threaded internal surfaces to suppress stray light and maximise contrast.
• Knurled grip: easy, secure threading on and off, even with gloves on cold nights.
• Lightweight and compact: just ~122 g, so balance on the mount barely changes.
• Dust caps included: keep the lens clean when not in use.

Technical specifications

Effective focal length by telescope

Nominal figures at the 0.63× design reduction. Actual reduction varies slightly with the distance between the lens and the eyepiece or camera sensor.

The C5 is found in Celestron's StarSense Explorer DX 5, NexStar 5SE, Astro Fi 5 and Advanced VX C5 packages, so the reducer suits those complete telescopes too.

Benefits

For visual observers

• Lower magnification and a wider field with your existing eyepieces, so large objects like the Orion Nebula, the Pleiades and Andromeda fit in view.
• Easier star-hopping and object finding thanks to the wider field.

For astrophotographers

• Roughly 2.5× faster imaging than at f/10 (exposure scales with the square of the focal ratio), cutting total integration time significantly.
• Wider framing of extended deep-sky targets.
• Less sensitivity to tracking and guiding errors at the shorter focal length.

For daytime use

• Works for terrestrial digiscoping and nature photography, allowing faster shutter speeds in low light.

Installation and use

1. Remove the visual back or any accessory from the rear of the SCT.
2. Thread the Reducer/Corrector onto the rear cell (C5–C9.25) or the reducer plate (C11/C14) until snug.
3. Attach your accessory to the reducer's rear thread: a 1.25" visual back, star diagonal, T-adapter with camera T-ring, or off-axis guider.
4. Refocus (focus position changes with the reducer fitted).
5. Replace the dust caps when finished.

Tip: for imaging, keep the camera sensor at the spacing recommended in Celestron's documentation to get the intended f/6.3 and the flattest field.

In the box

• Celestron Reducer/Corrector lens
• Front and rear protective dust caps

Recommended accessories

• Celestron 1.25" Visual Back
• Celestron Star Diagonal (1.25" or 2")
• Celestron T-Adapter for SCT + camera T-Ring (Canon / Nikon / Sony)
• Celestron Off-Axis Guider