Camera Lens EP
How to use a camera lens as an Eyepiece?
Camera’s such as SLR have removable lenses or
interchangeable lens. The best lens for this purpose is a
28mm, 35mm or 50mm.
WARNING the end of the lens that attaches to the camera
can have sharp metal parts that can damage your eye, so
cover these parts with something soft. Often lens come with
plastic end covers, you could drill a 16mm hole through the
centre of the cap and attach this.
We must be able to attach this lens to the telescope by
the thread in the front of the lens. This thread is normally
used to attach filters. Threaded rings to suit this thread
can be bought for about $9.00 and glued to a film canister
with the bottom end removed, as this will fit neatly inside
a 1 ¼” focusers.
Before we can use the lens we must adjust the settings.
Set the lens to the maxim F ratio (say 2.8) and set the
distance focusing to maxim distance (Marked 00)
Now attach the lens to the telescope by the front end and
view through the back of the lens with eye protection in
place. (See warning above)
Adjust the focuser, as if it were a normal eyepiece, you
will need to adjust the position of your eye to eliminate
the dark stop in the centre, which is created by the
secondary mirror in a Newtonian or Cassegrain type
telescope, practice on the Moon. The eye will be about 25mm
back from the lens, which will suit people who wear glasses.
See diagram below.
By Greg Walton
