What is the lens diameter of Seagull 4A?

Seagull 4A camera is the main product in the 4 series and the advanced version in the 4 series. It was once the standard configuration and main model for reporters at local newspapers and magazines. The photographic lens of the Seagull 4A is 75mm, with a diameter of 1:3.5, and a Kirk-style structure of three elements and three groups. The focal length of the viewfinder lens is the same as 75mm, but the aperture is 1:2.8, so that the viewfinder is bright and easy to view.