A compact astrograph defined by high quality and exquisite design. The NAKOH 60GT features a triplet APO optical system incorporating one Japan-made SD glass element and one ED glass element to minimise chromatic aberration. This design delivers consistently sharp, high-definition results with a flat, clear field extending to a 44mm full-frame image circle.
NAKOH is a Japanese optical manufacturer recently expanding into triplet APO astrographs with the launch of the 60GT series.
Founded to bring high-precision astronomy optics to advanced amateurs and astroimagers, NAKOH combines Japanese engineering with modern design.
Specifications 
| Aperture / Focal Length / Focal Ratio | 60mm / 360mm / f/6 |
| Objective Lens | Triplet APO (1× SD glass [Japan], 1× ED glass) |
| Image Circle | Ø44mm (with Reducer / Flattener) |
| Resolving Power / Limiting Magnitude | 1.93 arcsec / 10.66 |
| Light Gathering Power | 73× unaided eye |
| Tube Length | 270mm |
| Weight | ≈ 2.94kg |
| Rear Interface | 1.25″ / 2″ |
| Standard Accessories | 60GT OTA, Handle, Tube Rings, Dovetail Plate, 1.25″ Adapter, 2″ Adapter, Instruction Manual, Warranty Card |
Optical & Design Features
The NAKOH 60GT is a triplet APO astrograph using one SD glass element and one ED glass element to achieve superior chromatic correction.
By fully utilising the anomalous dispersion properties of SD and ED glass, the 60GT significantly reduces refractive index differences across wavelengths. This effectively suppresses chromatic aberration (especially purple and green fringing) while enhancing image sharpness and contrast.
Spot Diagram Performance
The horizontal axis represents the distance from the image centre, while the vertical axis represents the RMS radius of the star point. The 60GT achieves a central RMS radius of approximately 2μm and less than 2.5μm at the edge of the 44mm image circle, producing sharp, round stars across the full frame.
The longitudinal chromatic aberration graph plots wavelength against focal shift, illustrating the excellent colour correction of the optical system. The gentle, well-aligned curves indicate minimal focus shift across the visible spectrum.
Illumination & Vignetting Control
Relative illumination curves demonstrate high brightness retention from the centre to the extreme edges of the full-frame field. The smooth decline and wavelength consistency indicate excellent vignetting control.
Optical Testing & Quality Control
The optical performance of the NAKOH 60GT has been rigorously verified using a ZYGO interferometer. Test results show a Strehl ratio up to 0.976, an RMS value of 0.026λ (better than λ/38), and a PV value of 0.168λ—far exceeding the diffraction-limited standard.
| Ronchi Test | |
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In Focus 
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Out of Focus 
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The Ronchi test results show smooth, symmetrical line transitions both in and out of focus, confirming excellent surface accuracy and precise optical alignment.
Astrophotography Samples
Mechanical Features
