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an add-on dew and frost prevention accessory for the Telrad sight

Telrad Sight Pulser kit (66,137 bytes)

Above: Telrad Heater element with power cord and RCA phono style male connector (95,411 bytes).
Click on image to see enlarged view (210,656 bytes).

Telrad Sight Pulser kit (73,539 bytes) The Telrad sight is a versatile illuminated finder where the observer looks at a tilted glass window onto which is projected a red LED illuminated reticle pattern; this pattern appears suspended over the target area in space. Seeing through the sight and into the distance depends on being able to have the Telrad window remain free of dew or frost. Invariably, telescopes are used at night and often in areas where dew can form. Dew is moisture naturally found in the air that condenses onto surfaces when their temperature cools down to the 'dew point', at this temperature materials including the glass window of the sight become a condenser so a fog will form across the window and it becomes opaque. To prevent this occurrence Company Seven offers two optional solutions:

    1. Telrad Dew Shield a passive flip-up hood

    2. Telrad Window Heater Element - an active, powered resistive heater element that works with an optional heater controller

The Telrad Window Heater Element is powered by 12 volts dc with the current regulated by an optional heater controller. The power cord is provided with an RCA phono style male connector so that it can plug into one of the sockets of controllers offered by Company Seven. The controller in turn plugs into a 12 volt DC power source, this can be a battery or an AC to DC Power Supply.

Right: Heater element installed in the Telrad window, it reduces the field somewhat but all Telrad reticle circles remain visible.

The Window Heater Element accessory for the Telrad sight is installed by the user, and no tools are needed. Simply slide the heater element onto the window of the sight, into the void between the Telrad lens and display window as shown at right.

A side benefit of the heater is that in freezing conditions, this can prevent frost (from operators breath for example) from forming on the window.

Operation of the Telrad Window Heater Element:

  • Install the Window Heater Element onto the Telrad.

  • Connect the male connector into a compatible variable 12 volt controller.

  • When setting up the telescope, any heater element(s) should be installed and powered on even while setting up - ideally before the observing session begin.

  • Company Seven recommends running the element at 50% power setting to start. This should be more than satisfactory in most conditions. If dew does start to form, then turn the power up higher as conditions warrant. If dew continues to accumulate then double check the power source to assure adequate voltage.

  • In the worst dew prone environments the heater may work best in conjunction with the optional Dew Shield


    Operating Voltage: 12 volt DC
    Power Cord Length: 6 feet (182.9 cm)
    Weight: 1.6 oz. / 48 g
    Installation Tools required: None
    * Specifications are subject to change without notice.

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