Convergent FA20

FA telescopes FA telescopes

Telescope Name: Convergent FA20

Telescope Price: $32,895

Item #: CFA20

The AG Optical Systems Convergent Fast Astrograph .5 meter (20 inch) F5 telescope is an observatory-class imaging instrument featuring a huge 60mm flat field free from astigmatism and coma. The outstanding optical performance of the FA20 is made possible through the convergence of careful design, state-of-the-art manufacturing, and precise assembly. Wide field images are captured with high-contrast details and sharp stars across the entire field of view.


The AG Optical Systems FA20 F5 optical system provides exceptional thermal stability. Low expansion optics ensure the figure and focus stability of the Convergent FA20 as the temperature changes over the course of an imaging session. When combined with the rigid, thermally stable carbon fiber truss tube assembly of the FA20 you can expect to spend less time focusing and more time collecting data.

AG Optical Systems FA series carbon fiber truss optical tube assemblies make extensive use of carbon fiber composite materials, CNC-machined components, and precision collimation adjustments to provide a rigid and thermally stable platform for the low expansion optics. Three cooling fans speed the cooling of the primary mirror while primary and secondary mirror heaters can be automatically controlled by the optional Thermal Control System (TCS).

The optional, robust, digital Optec Gemini rotating focuser is ASCOM-compatible is capable of precision focusing and rotation while carrying heavy CCD imaging trains.

Optical Tube Assembly

  • 150 lbs. carbon fiber tube assembly
  • Tube length: 43.5 inches
  • 20″ (.5m) low expansion substrate F5 optical system
  • 60mm corrected imaged circle. 1.4 degrees
  • Cooling fans and optional Thermal Control System
  • Dust covers
  • All CNC components, all stainless steel fasteners

Optical System

  • 20″ F5 corrected optical system with integral field corrector
  • 2500mm focal length
  • 11″ secondary obstruction (55% linear obstruction)
  • Performance: 5 micron RMS 15mm off-axis, 6 micron RMS 25mm off-axis
  • 6.5″ of back focus from Optec Gemini focuser
  • 96% enhanced aluminum coatings
  • 4.7″ of back focus with Optec TCF-S3i focuser installed


Truss shroud

Truss Shroud

Heavy Lycra shroud to block stray light, mitigate dust intrusion

Price: $195
Item #: FA20SHROUD


optec gemini 3.75

Optec Gemini 3.75″ Rotating Focuser

Low profile (2.5″), rotating digital focuser with 20 lbs payload capacity, temperature compensation feature

Price: $3495
Item #: GEMINI

thermal control system

Thermal Control System

Computer-based automated control of primary mirror cooling, primary and secondary mirror anti-dew control

Price: $995
Item #: TCS


Piggyback Dovetail Plate

CNC-machine 6061 aluminum Losmandy “D” profile piggyback dovetail plate

Price: $295
Item #: FA20PIGGY

Optec TCF-S3i 3″ Digital Focuser

Robust, digital 3″ focuser with temperature compensation

Price: $1495

Item: TCFS31



  • Carbon fiber optical truss tube assembly
  • Losmandy “D” mount dovetail
  • Primary and secondary dust covers
  • Primary mirror cooling fans with power cable
  • Low expansion substrate optics with enhanced aluminum coatings
  • All stainless steel fasteners and springs
  • Backplate carrying handles