I think there's just a metal tab that gets in the way, and you can bend it. I have a 1959 version. The shutter is 1/40s and the apeture is around f16, maybe f22. I shoot b&w film in it, usually ISO 400. I vary exposure by using filters to eat up 1, 2, 3 stops of light as needed. Usually those filters are a yellow, orange, or red. Sometimes I use ND.
Kent in SD