The special full-frame reducer of 61EDPH Ⅲ: One end of the thread is M68 × 1, connected to the focuser; the other end of the thread is M48 × 0.75 and has a built-in 2" filter thread. The back focus is 55mm. If it needs to be extended, the adapter can be screwed down to reveal the M54 × 0.75 male thread, and the back focus becomes 75mm. The focuser adopts a quadruplet air-spaced structure, supporting full-frame imaging. With the reducer, the focal ratio of 61EDPHⅢ is reduced to F4.4 and the focal length is reduced to 270mm, making the telescope the first choice for deep sky astrophotography.