Theta Optics Open II Red Dot Reflex Sight

Theta Optics
Code: THO-10-009053
  • Alloy construction
  • Integrated 20mm rail mount
  • Red/green illumination - 4 reticle types

Those looking for an affordable reflex sight which combines the strength of military style designs with the functionality of the more common open reflex sight, check this out! The Theta Optics Open II is an upgraded version of existing open reflex sights with a redesigned alloy housing to provide greater protection in the even the sight is dropped or bumped during a skirmish. 

The usual functions of the open reflex sight are still present, with red or green illumination and several brightness levels to choose from, and selectable reticles via the dial at the rear of the sight. This sight also comes with a 20mm Picatinny rail mount built in, meaning an easy and secure fit on any Airsoft gun with a 20mm Picatinny rail!

Full description


The Theta Optics Open II is an upgraded version of the common open reflex sight, offering a redesigned housing to protect the lens from the bumps and scrapes which often occur in energetic applications. The sight is easy to use and comes pre-installed on its' own 20mm RIS mount which will attach to any compatible 20mm Picatinny rail system.

The sight requires 3x LR44/AG13 button cells to power it, and 3 are included in the box to get you started. Like many popular ACM sights, you have a choice of four reticles suited different scenarios and ambient light conditions which can be selected by turning the dial at the rear of the sight. On either side of the sight body, you will find the activation switches, marked "ON GREEN" and "ON RED", and pressing either of these buttons will activate the sight in the chosen colour. Brightness adjustment is achieved by pressing the buttons repeatedly to scroll through the brightness settings, and holding both buttons simultaneously will turn the sight off. 

If you have been considering an open reflex sight the Theta Optics Open II would make a fine choice for skirmishing with its more robust design and protective housing, preventing the sight from being shattered from a bump or scrape. Its multiple reticle types offer a wealth of functionality and its low price saves you some cash to invest in a lens protector!


  • Open reflex style
  • Alloy construction
  • Red/green reticle with brightness adjustment
  • Windage and elevation adjustable - Allen key included
  • Integral 20mm Picatinny rail mount
  • Battery: 3x LR44 button cell (included)
  • Backup rear ironsight built in
  • Four reticle types - Dot, cross, ringed cross and ring
  • Robust design - Housing protects the lens from drops/bumps
  • Theta Optics branded

Package Includes

  • Theta Optics Open II Red Dot Reflex Sight
  • Allen Keys
  • Cleaning Cloth
  • Manual
  • 3x LR44 Cells



Parts & Accessories Type
Sights and Scopes
Sight Type Icon
Sight Type
Red Dot Sight
Package Includes
Instruction Manual, Battery, Cleaning Cloth,

Weight and Dimension

Product Height
Approx. 5.8cm
Product Length
Approx. 9.2cm
Product Width
Approx. 4.2cm
Weight KG Icon
Weight (KG)
Approx. 0.143kg


Colour Wheel Greyscale
Item Colour
Construction Icon
Alloy shell and mount. Glass lens. Polymer rear housing. Steel mounting bolts and adjustment screws.

Sight Specific

Sight Magnification
Sight Adjustment Adjustments
Windage, Elevation, Multiple Reticle Types,
Sight Zero Adjuster Method
Adjustment Tool Required, Hex / Allen Key,
Sight Zero Location
Top, Left,
Sight Mount Options
Integrated Rail Mount
Sight Objective Lens Diameter
Reticle Type
Multiple Reticle Types

Illuminated Sight Specific

Illuminated Reticle
Illuminated Reticle Colours
Red, Green,
Battery Type
LR44 / LR154, AG13 / SG13,