Fach-Prism Triangle 3 Filter - 49/55mm

Prisma filters are rotating prism filters that duplicate part of your image depending on your model (parallel, prism...).

You can find out the filter thread size of your lens by measuring the internal thread; it does not correspond at all to the focal length: for example, a 50mm 1.8 lens can have a 49, 52 or 55mm thread...