Collimation eyepiece for refractors and Newtonians (short)

Collimating eyepiece (long) is a device with a reticle on one end. Place the eyepiece onto the focuser and align the optical elements using the reticle. The longer one is for Newton relectors while shorter ones can be used for refracting telescopes. During nighttime the device can be used if it is illuminated from its side, in this case the illuminated disk should be seen as a bright disk in the secondary and primary mirror.

The collimating eyepiece (short) one is a similar but much shorter design that can be used by checking the light reflected from the main objective lens or mirror. It can be used for refractors, or Newtonian telescopes as well.