In 1840 the Petzval portrait lens was manufactured in Vienna Austria by Joseph Petzval. The Petzval lens is a portrait photographic lens that is made of a heavy brass metal compared to the light metal and plastic in recent lenses. Most camera lens manufacturers find it difficult to achieve a focal length 160mm with one of the fastest f-stop f/3.6 but the Petzval portrait lens was the first lens that still creates a little shallow depth of field. It is one of the first lenses ever, and on the body, it has a silk metal that allows you to change the aperture of your choice, i.e you can change the aperture of the lens using the silk tool at the middle of the lens. This lens can also be mounted on other cameras such as the Canon EF, Nikon F mount etc.
https://www.petermckinnon.com/ speaks in the YouTube video on how this lens was been used by the older photographers.
Video source: YouTube
