Telrad Dew Shield
                                   

Telrad Dew Shield Project

This webpage documents construction of a dew shield for a Telrad zero power pointing device. The goal was to find a simple and inexpensive solution to prevent dew formation on the Telrad. This project required about 30 min. construction time and cost less than $5. 

Prototype Telrad Dew Shield

I have previously constructed an inexpensive Telrad dew heater that prevents dew formation on the glass Telrad viewing window (see the Homemade Telrad and Eyepiece Dew Heater Webpage). Eventually the D cell batteries that power the dew heater ran out of charge and I forgot to replace them. While setting up for the next observing session I remembered that my Telrad dew heater was out of power. It took about 3 min. to make a very simple Telrad dew shield, which prevented dew formation during my entire observing session. The prototype dew shield is just a section of foam used as an underlay for laminate flooring; this is the same material I used to construct my SCT and RGB filter dew shields (see the SCT Dew Heater and RGB Filter Slider Dew Shield Webpages). I just cut out a small foam section and pressed it into the recess around the top of the Telrad glass plate to keep the Telrad covered when not in use (below photo). This dew shield functioned satisfactorily and kept my Telrad dew free, however it was difficult to remove/replace when wearing gloves.


Final Telrad Dewshield

The final dew shield is just a slight modification of the prototype, where I added a plastic tab to make removal simpler. I considered attaching the dew shield with Velcro so that it could be hinged, but eventually decided that simpler was better and not to over engineer a simple solution. The below left photo shows the basic materials: a scrap of clear polycarbonate hobby plate and a small square of foam with one side covered with aluminum tape. The below right photo shows the finished Telrad dew shield. The polycarbonate is taped to the foam with clear packaging tape, covered by a final layer of aluminum tape. The bottom of the dew shield is not covered with tape because the foam is a soft surface that shouldn't scratch the glass viewing plate. The large plastic tab makes it possible to remove/replace the dew shield while wearing gloves.

 

Below are three photos showing the final Telrad dew shield installed on my C8:

 


   

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