92GX

Package Contents

Optical Tube Assembly (OTA)

Handle

Tube Ring

Dovetail Plate

1.25-inch Eyepiece Adapter/ 2-inch Eyepiece Adapter/ Imaging Adapter

UserManual/  WarrantyCard

Specification

Design Features

* The NAKOH 92GX is a quintuplet Petzval astrograph, utilizing one piece of SD glass(Japan-made) and one piece of ED glass.

It fully leverages the anomalous low dispersion characteristics of both SD and ED glass to significantly reduce differences in the refractive index across various wavelengths. This effectively suppresses chromatic aberration (particularly purple and green fringing) and enhances image sharpness. The lens surfaces feature a multi-layer coating process that effectively suppresses stray light while significantly improving light transmittance and reducing reflection loss, ultimately delivering brighter and sharper images.

Optical Path Diagram

The classic Petzval design consists of four glasses arranged in two groups (two at the front and two at the rear), its flat-field design can prevent star deformation and eliminates the need for additional field flattener, significantly enhancing image quality. 

Building upon this classic design, the 92GX features a deep advancement: the front group has been upgraded from a traditional cemented doublet to an air-spaced triplet, while the rear group consists of an air-space doublet. By using air-spaced front and rear groups to correct spherical aberration and coma, it achieves a flat field from the center all the way to the edge of medium format(55mm), delivering exceptional images with uniformly sharp stars, all without an additional field flattener.

*92GX（Focal Length: 598mm·F6.5） Camera：

φ44mm

APS-C

* The 92GX is not only built for astrophotography but also serves as a high-performance instrument for observation.

Its 92mm aperture provides ample light-gathering ability, and combined with an F6.5 focal ratio, it delivers clear details whether observing natural landscapes or lunar craters. Thanks to its excellent aberration correction, the overall optical performance approaches that of an aberration-free system. Even at high magnifications, chromatic aberration remains absent, offering a flat and sharp field of view. Paired with a dual-speed focuser, fine focusing becomes effortless, allowing users to quickly immerse themselves in the pure joy of visual exploration.

* Spot diagram

92GX Spot Diagram

The imaging quality of the optical system can be evaluated by analyzing the distribution of star points in the image.The horizontal axis represents the distance of the star point from the image center, while the vertical axis represents the RMS radius of the star point.

The RMS radius of the central star point for the 92GX is less than 1.2 micrometers, the star point radius at the edge of the 44mm frame is less than 2 micrometers, and at the edge of the 55mm image circle it is less than 2.7 micrometers. The stars are sharp and rounded, demonstrating excellent performance across the medium format (55mm).

Relative illumination

The relative illumination uses the field radius as the horizontal axis and relative brightness percentage as the vertical axis to illustrate the attenuation of light from the center to the edge of the field of view.

 The 92GX delivers excellent relative illumination across the full frame, with a smoothly declining curve from the center to the edge of the 55mm image circle. Even at the edge of the 55mm image circle, relative illumination remains close to 100%, effectively minimizing vignetting