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.
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.
The basic idea is quite simple: take an unused eyepiece, insert a
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
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.