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20/25/28/30/35/40/42/45/ 50/54/60/70/80/90mm Astronomical Telescope Secondary Mirror

20/25/28/30/35/40/42/45/ 50/54/60/70/80/90mm Astronomical Telescope Secondary Mirror

20/25/28/30/35/40/42/45/50/54/60/70/80/90mm elliptical secondary mirrors for DIY Newtonian reflective astronomical telescopes. Each mirror has a short axis dimension, aluminum coating with protective film, and is designed to match specific primary mirror apertures. Available in 14 sizes with tolerance ±0.5 and surface accuracy PV 1/4–1/6λ.

  • 14 standard sizes from 20mm to 90mm short axis for matching various primary mirror apertures
  • Aluminum coating with protective film for high reflectivity and durability
  • Tolerance ±0.5 ensures consistent fit and alignment in telescope assembly
  • Surface accuracy PV 1/4–1/6λ supports sharp image quality in reflective telescope systems
  • Elliptical shape optimized for Newtonian telescope optical path and light collection
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Technical features

  • Secondary mirror type: elliptical plane mirror
  • Available sizes: 20, 25, 28, 30, 35, 40, 42, 45, 50, 54, 60, 70, 80, 90mm short axis
  • Short axis refers to the length of the short side diameter
  • Tolerance: ±0.5 mm
  • Surface accuracy PV: 1/4–1/6λ
  • Coating: aluminum reflection with protective film
  • Surface finish: aluminized with protective layer for long-term performance
  • Package: 1 piece per unit

Who it is for

  • DIY telescope hobbyists building Newtonian reflectors
  • Educational suppliers providing telescope assembly kits
  • Small-scale telescope manufacturers sourcing secondary mirrors
  • Astronomy clubs sourcing replacement or upgrade mirrors

Specifications

Models20 / 25 / 28 / 30 / 35 / 40 / 42 / 45 / 50 / 54 / 60 / 70 / 80 / 90mm
Short Axis20mm to 90mm
Tolerance±0.5 mm
Surface AccuracyPV 1/4–1/6λ
CoatingAluminum reflection + protective film
ShapeElliptical plane mirror
Package1 piece per unit

Use guide

  • Match the secondary mirror short axis to the primary mirror aperture for optimal performance
  • Use 20mm mirror with 76mm aperture main mirror; 25mm with 114mm; 35mm/40mm with 127mm–150mm; 70mm with 203mm
  • Ensure the telescope tube diameter and focuser allow space for the selected mirror size
  • Handle with care to avoid scratching the coated surface

FAQ

What does short axis mean?
Short axis refers to the length of the short side diameter of the elliptical mirror.
Which mirror size fits a 150mm aperture main mirror?
35mm or 40mm short axis secondary mirror is suitable for a 150mm aperture reflector.
Is the coating durable?
Yes, the mirror has an aluminum coating with a protective film to prevent oxidation and damage.
Can I use a 70mm mirror with a 135mm main mirror?
Yes, a 70mm short axis mirror is suitable for 135mm aperture reflector main mirrors.
What is the tolerance?
The tolerance is ±0.5 mm on the short axis dimension.
Is the mirror ready to install?
Yes, the mirror comes with aluminum coating and protective film, ready for installation.
How many mirrors are in one package?
One piece per package.

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