GSO GSO focal reducer from Modern Telescopes, India's authorized distributor. 
 
GSO 0.75x focal reducer (not a field flattener) for Ritchey-Chretien telescopes
Enables a wider field of view and shorter exposure times for astrophotography
Fully multi-coated optical components allow for excellent image color and contrast
Provides 80mm of back focus
Ideal for cameras sensors with a diagonal of 15mm or less
Threads into eyepieces, camera adapters, and other accessories with standard 2" threads, and can be stacked with additional 2" threaded accessories and spacers
Designed for use in GSO Ritchey-Chretien and other compatible RC telescopes, this two-element optical component reduces the scope’s effective focal length by 0.75x. It takes an f/8 scope to f/6 or an f/9 scope to f/6.75, making it easier to capture faint detail in astrophotos with shorter exposure times.
The focal reducer is carefully designed and manufactured with fully multi-coated optics to retain image color, brightness, and contrast. Although it’s not a field flattener, this reducer helps retain the inherent field flatness of an RC scope.  It’s ideal for astronomy cameras with sensor diagonals as large as 15mm.
The GSO 0.75x focal reducer provides about 80mm of back focus, enough to accommodate off-axis guiders and filter wheels. The black-anodized body slips into a 2” focuser or adapter, and it secures accessories with 2” barrels using a non-marring compression ring.
On the scope side, the reducer includes a 2” barrel with female M48x0.75 threads. The camera side has a 2” female tube that accepts cameras with 2” nosepieces. The 2” tube can be unscrewed, revealing a male M48x0.75 thread. An M48-M42 step-down adapter is included.