This very simple LED fixture makes the reticle in a polar scope visible when aligning a telescope in the dark. You will need to physically dim the LED, for instance by covering it with nail polish.

Features

• battery compartment also acts as a switch (and very addictive fidget toy)
• you can still use the original cap to cover the alignment scope.

This design does not include a current limiting resistor, which will likely shorten the lifetime of both the battery and the LED. Also the LED pins need to be aligned properly to prevent short circuiting the battery. Generally, it all just works though.

Rationale

For some reason, my Skywatcher EQM-35 mount comes with a polar scope, but without illuminator. In my experience, aligning the scope in the dark without illumination is close to impossible, so after some days of fiddling with torch lights and trying to align the scope with one hand, I decided enough is enough.

A commercial scope illuminator is available, but it happens that in the current time frame (in the midst of Covid-19 lockdowns), many telescopes and telescope supplies are sold out in most places and require days to weeks for delivery.

Excellent reason then to design and print my own...