Homemade Illuminated Reticle Eyepiece

Illuminated Eyepiece Project

This webpage documents construction of an inexpensive, homemade illuminated reticle eyepiece. This project required about 1 hour construction time and only cost $2.25.

An illuminated eyepiece is an important accessory for accurate polar alignment and guiding corrections during astrophotography. A commercial illuminated eyepiece will cost between $60-$120, but my homemade illuminated eyepiece cost only 
$2.25.  The following instructions are for a 0.965 inch. diameter eyepiece, but the same procedure could also be used to construct an illuminated 1.25 inch. eyepiece.

I have used this eyepiece to drift align my C8 and it functioned as well as a commercial illuminated eyepiece.

Eyepiece Construction

The basic idea is quite simple: take an unused eyepiece, insert a small etched glass reticle inside the eyepiece barrel, drill a tiny hole through the barrel, and illuminate the reticle with a small bicycle light.  The below photo shows a 21 mm glass reticle (purchased from Surplus Shed) illuminated with an ordinary LED bicycle light.

Below is a photo showing the required parts (clockwise from upper left): 0.965 inch. eyepiece lens,  scrap plastic tube, 0.965 inch. eyepiece barrel, LED bicycle light, field stop cut from scrap plastic tube, and 21 mm glass reticle.

The scrap plastic tube is approx. 0.965 inch. O.D. at the top and transitions to a smaller diameter at the bottom (instructions are also provided for using a standard plastic tube with a single inner diameter). The glass reticle fits inside the plastic tube and sits at the restriction formed where the tube narrows; if you can't find this configuration tube, just fabricate an extra field stop to support the reticle (described in the next paragraph). The below photo shows the reticle inserted into the plastic tube. Note how the reticle sits on the plastic shoulder.

The reticle is held in place by a field stop (below photo). The field stop is just a small strip of the same plastic tube, with a small section removed (see the required parts photo). The field stop is pinched (bent) and inserted inside the plastic tube. Friction holds the field stop in place. Note that if you are using a standard section of tube (the same diameter along the entire tube length) then fabricate two field stops. Place one field stop on each side of the reticle.

Assemble the eyepiece and check that the reticle is in focus. If out of focus, adjust the reticle position until it is in focus. Measure the reticle position, then remove the reticle, and drill a small hole into the plastic tube at the reticle position. The hole diameter will depend on the size of the bicycle LED light . Reassemble the plastic tube and reticle-field stop assembly. Attach the eyepiece lens with tape or some other suitable means. Place the plastic tube on top of the 0.965 inch. barrel and secure with tape. The completed assembly should look like the below photo (note that the glass reticle is visible through the small illumination hole):

I fabricated a small plastic plate to hold the bicycle light perpendicular to the eyepiece barrel as shown below:

The completed eyepiece attached to a C90:

Below are two photos taken with the illuminated reticle eyepiece: the left photo shows how the illuminated reticle appears inside the eyepiece and the right photo shows my neighbor's holiday decorations through my C90.