An eyepiece suitable for a night vision device, having an optical combiner for injecting a synthetic image onto the scene and having a single optical correction mechanism is provided herein. The eyepiece may include an observer-side lens; an objective-side lens; a diopter adjustment knob configured to set a distance between the observer-side lens and the objective-side lens; and an optical combiner located between the objective-side lens and the objective-side lens, wherein the optical combiner reflects towards the observer-side lens, the synthetic image transmitted from outside the eyepiece and transfers towards the observer-side lens, a scene image coming from an objecting lens of the night vision device and passing through the objective side lens, and wherein the diopter adjustment knob serves as a single setting mechanism which simultaneously sets a diopter of the observer and a focal depth of the display source image.