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Focal Reducer

Focal Reducer is an optical element used to reduce focal length, increase lens speed, and in some instances improve optical transfer function (OTF) performance.

Popular applications include photographyvideography, and astrophotography. In astrophotography, these qualities are most desirable when taking pictures of nearby large objects, such as nebulae.

GSO 0.5x Focal Reducer 1.25" with 25mm extension tube Rs 1740 + 18% GST
0.5x focal Reducer 1.25" for Visual & Astrophotography.

GSO's 1.25" 0.5x focal reducer screws on to any accessory such as eyepieces, camera adapters, etc. that accepts standard 1.25" threaded filters and provides a nominal reduction of 0.5x. Use of this focal reducer effectively halves the focal ratio of your telescope, resulting in a wider field of view and significantly shortened exposure times for astrophotography. For example, use of this reducer will convert an f/10 telescope into an f/5 scope.

The 2-element reducer features fully multi-coated optics in a black-anodized aluminum filter cell. It also has additional 1.25" female threads so you can screw/stack additional 1.25" filters on to this reducer. This focal reducer will work well for visual use too when coupled with the right kind of eyepieces and telescopes; it is not recommended for very fast scopes or very wide angle eyepieces for visual applications.
Free aperture 22.5 mm
Optical system multi-coated doublet
Reducing factor 0.5x (depending on the projection distance)
Function 0.5x Reducer for Visual and Astrophotography
Max. distance to the camera sensor approx. 55 mm
Connection 1.25" filter thread (M 28.5 x 0.6) on both sides

GSO 0.5x Focal Reducer 2" Rs 2280 + 18% GST
0.5x focal Reducer 2" for Visual & Astrophotography.

The GSO 0.5x focal reducer provides a nominal reduction of 0.5 times. The actual focal length reduction will vary a little over or under 0.5x depending on where the focal reducer is placed exactly in the optical path.

The reducer features 2-element fully multi-coated optical design and blacked lens edges in a black anodize aluminum filter cell.

It comes with outside thread M48x0.75 to fit with most 2" eyepieces the additional 2" filter thread inside accept all kinds of 2" color filters.
Free aperture 45 mm
Optical system multi-coated doublet
Reducing factor 0.5x (depending on the projection distance)
Function 0.5x Reducer for Visual and Astrophotography
Max. distance to the camera sensor approx. 55 mm
Connection Filter thread 2" (M48x0.75)
2" filter thread on both side

GSO 0.75x Focal Reducer 2" - SOLD OUT Rs 4800 + 18% GST
  • 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.
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