DeltaOptical RC 0.75x 2″ Focal Reducer and Field Corrector
Overview
The DeltaOptical RC 0.75x 2″ focal reducer is specially designed for Ritchey-Chretien telescopes with a large backfocus. With a correction factor of 0.75x, it shortens the focal length while increasing the telescope's light-gathering ratio from f/8 to f/6. At the same time, the field of view is expanded by a factor of 1.25x - an advantage that is especially valuable when photographing extended deep-sky objects.
This accessory serves two functions simultaneously: it acts as a focal reducer and as a field corrector, making it a versatile and cost-effective upgrade for any RC telescope setup.
Optical Performance
The corrector improves the linearity of the optical field and increases the linear size of the corrected imaging area. In practice, astrophotography cameras with sensor diagonals of up to 44 mm can be used without visible degradation of the image in the corners of the frame.
This makes the reducer compatible with full-frame cameras and large CCD sensors - a popular choice among experienced astrophotographers who demand the highest image quality across the entire field.
Mechanical Design and Compatibility
The reducer slides into a standard 2″ focuser drawtube. Its features include:
- Telescope-side connection: standard 2″ fitting with a filter thread, allowing easy addition of astronomy filters
- Camera-side connection: removable 2″ eyepiece holder and an M48 thread beneath it
- Working distance: greater than 80 mm from the optical tube, leaving ample space for additional accessories
- Included in the box: M48/T-2 adapter for connecting a DSLR camera or CCD camera
The generous working distance of over 80 mm means there is plenty of room in the optical path for accessories such as an off-axis guider or a filter wheel - making this corrector an excellent choice for advanced imaging setups.
Technical Specifications
| Parameter |
Value |
| Reduction factor |
0.75x |
| Field of view expansion |
1.25x |
| Aperture ratio change |
f/8 to f/6 |
| Compatible telescope type |
Ritchey-Chretien (RC) with large backfocus |
| Focuser connection |
2″ standard |
| Filter thread (telescope side) |
2″ standard filter thread |
| Camera-side thread |
M48 |
| Maximum corrected sensor diagonal |
44 mm |
| Working distance from optical tube |
greater than 80 mm |
| Included adapter |
M48/T-2 |
Who Is This Reducer For?
The DeltaOptical RC 0.75x focal reducer is ideal for:
- Astrophotographers who want to get the most out of their Ritchey-Chretien telescope
- Users of full-frame DSLR or mirrorless cameras and large-format CCD or CMOS sensors
- Imagers looking to reduce exposure times by gaining a faster focal ratio
- Those building advanced setups with off-axis guiders, filter wheels, or electronic focusers
- Anyone who needs a wide, well-corrected field for photographing nebulae, galaxies, and other extended deep-sky objects
About DeltaOptical
DeltaOptical is a brand founded by passionate astronomers with the goal of offering high-quality optical accessories for both visual observation and astrophotography. The brand's philosophy is straightforward - to create products that genuinely meet the practical needs of astronomers in the field.
The DeltaOptical range covers a wide variety of accessories, from eyepieces and filters to focal reducers and field correctors, with a consistent emphasis on optical quality and precise mechanical construction. Customers appreciate the reliability and competitive pricing that make professional-grade astronomical equipment accessible to a broader community of enthusiasts. DeltaOptical products are designed to integrate smoothly into existing setups and enable quick, easy upgrades.
