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Stargazing June 15th ✦ 6pm-10pm
Stargazing June 15th ✦ 6pm-10pm

Starizona Nexus 0.75x Newtonian Focal Reducer/Coma Corrector

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Turn your Newtonian telescope into a fast, high-quality astrographic instrument with the Starizona Nexus focal reducer.

Newtonian telescopes require a coma corrector in order to give sharp stars over a large field of view, but most coma correctors keep the telescope's native focal ratio or even make the scope slower. The Nexus instead acts as a coma corrector and also provides a 0.75x focal reduction factor. This turns a common f/4 Newtonian into an f/3 system, giving a larger field of view and reducing exposure times by a factor of 1.8x.

The Nexus incorporates extra-low dispersion (ED) glass in a sophisticated optical design that gives performance equal to the best coma correctors while decreasing, instead of increasing, the focal length. The Nexus is also designed to be parfocal, so it does not change the original focal point of the telescope. The corrected image circle is 28mm, accommodating camera sensors up to APS format. While nominally designed for the popular commercial f/4 imaging Newtonians, the Nexus can work with Newtonians as fast at f/3.

Backfocus requirement for the Nexus is 55mm, matching the common standard for most coma correctors, field flatteners and focal reducers. This distance allows for the use of DSLRs as well as mirrorless cameras and most astronomical CMOS and CCD cameras. The Nexus has M48 threads on the camera side. The barrel of the Nexus is a standard 2" diameter to fit most focusers. On the telescope end are M48 threads for a standard 2" filter.


  • Focal Reduction Factor: 0.75x
  • Image Circle:  28mm (APS format)
  • In-Focus Required: None (parfocal)*
  • Backfocus: 55mm
  • Camera Threads: M48 x 0.75
  • Filter Threads: M48 (2" mounted)
  • Barrel Size: 2"
  • Overall Length: 3.14" (80mm)
  • Weight: 0.74 lbs (335g)

* Some slower Newtonians that were originally intended for visual use will not reach focus with some cameras using the stock focuser. The Nexus preserves the original focus point of the telescope, so if the camera can reach focus without the Nexus it will reach focus with it. However, note that the Nexus (and most other coma correctors) require a 55mm backfocus. This means the camera has to be able to focus with that much backfocus. A CMOS camera that has a backfocus of 17.5mm, for example, might reach focus on a certain Newtonian but would not when the backfocus is extended to 55mm as required by a coma corrector. Most commercial f/4 Newtonians are designed with plenty of backfocus for a coma corrector because they are intended for photography. But some slower Newtonians intended for visual use do not have enough backfocus for a coma corrector and camera. Please feel free to contact us if you are unsure of your telescope's compatibility.