The Mobile phone holder compatibles with binoculars or monoculars that eyepiece outer diameter between 1.1 inch to 1.89 inch (28mm to 48mm).
The Mobile phone holder fits spotting scopes with straight eyepiece or angled eyepiece less than 1.89inch (48mm).
The Mobile phone holder works with microscopes with the eyepiece outer diameter between 1.1 inch to 1.89 inch (28mm to 48mm).
The Mobile phone holder fits astronomical telescope with the eyepiece outer diameter between 1.1 inch to 1.89 inch (28mm to 48mm).
Put holder into the eyepiece, then turn the knob clockwise to fix firmly.
Turn the knob counterclockwise to extend the clamp width until it can put the phone into the clamp.
Put the phone into the clamp, adjust the phone position so that the phone camera and eyepiece focus on the alignment, and finally fix the phone firmly.