Rigel Systems PulsGuide Guiding Eyepiece Illuminator (without eyepiece) with Battery Pulses the Reticle Illumination of a Guiding Eyepiece During an Exposure Invaluable for Guiding on Very Faint Guide Stars PulsGuide Keeps the Crosshairs Bright Track Stars that are Virtually at the Limit of what you can See in the Eyepiece