Specification

Design Features

* The NAKOH 60GT is a triplet APO astrograph, utilizing one piece of SD glass and one piece of ED glass.

Optical Path Diagram

It fully leverages the anomalous 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 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 NAKOH 60GT achieves a central star RMS radius of approximately 2 micrometers, and less than 2.5 micrometers at the edge of the 44mm image circle.

The stars are sharp and rounded, demonstrating excellent performance across the full frame.

60GT Longitudinal chromatic aberration Curve

The longitudinal chromatic aberration graph uses wavelength (nm) as the horizontal axis and focal shift (μm) as the vertical axis to display differences in the focusing positions of various wavelengths along the optical axis. The NAKOH 60GT exhibits low shift, a gentle curve across the entire wavelength range, and well-aligned curves at key wavelengths, reflecting its excellent chromatic aberration control.

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. Even at the extreme edges of the full frame, the 60GT maintains high brightness, a smoothly declining curve, and consistency across multiple wavelengths, effectively minimizing vignetting.

The optical performance of the NAKOH 60GT has been rigorously tested using the internationally recognized ZYGO interferometer, with quantitative data demonstrating top-tier excellence.  
The test report reveals a Strehl ratio as high as 0.976, an RMS value as low as 0.026λ (surpassing λ/38), and a PV value of 0.168λ. These figures not only far exceed the demanding "diffraction-limited" standard (Strehl ratio > 0.8) but also indicate that its imaging quality is virtually unconstrained by mirror precision, allowing celestial details to be concentrated into an exceptionally sharp focus.  

The Ronchi test quantitatively evaluates the surface figure accuracy and optical axis collimation of the objective lens by analyzing shadow patterns. The 60GT demonstrates exceptional performance: both in and out of focus, the shadow variations transition evenly and smoothly, forming straight, symmetrical lines. 

This conforms to the criteria of an excellent optical system, indicating that the 60GT possesses precise parabolic surface figures and optimal optical alignment.