"Focusing" with fixed-focus lenses?

[Eric McCammond]

I'm brand new to cine cameras and have a Bolex B8 with Pizar 5.5mm f/1.9 lens.  Each lens aperture setting has a correlating distance.  For example f/1.9 has a distance of 50cm.  I'm assuming, at f/1.9, the camera is focused f/1.9 to ∞.  So, essentially, if I keep my subject at least 50cm from the film plane, my subject will be in focus.  Is this correct?  Based on my experience with still cameras, it seems quite forgiving for an f/1.9 aperture but otherwise seems to make sense.

[Dom Jaeger]

Fixed focus lenses are normally set to around the Hyperfocal distance or closer, so maybe 2.5 or 3 m. This allows the maximum depth of field. At f/1.9 your lens has a close focus minimum of 50cm, but you can test it yourself to see just how sharp things are that close. Stopping down will increase your depth of field and allow you to get closer to your subjects. A 5.5mm lens has a lot of depth of field even wide open.

[Joerg Polzfusz]

Hi!

Depending on your lens, it’s most likely set to something between 2m and 10m. The only thing that changes with the f-stops are the near distances and the hyperfocal distances. (The far distances also changes, but fix-focus-lenses are usually designed to have a far distance that only changes from 100m to „endless“, so you can ignore it.)

Use a depth of field calculator (there are also free tools on the web) and try to figure out whether your numbers are the hyperfocal or the near distance. Or do it like everyone did in the past with these lenses: simply ignore focusing - they simply work.

Jörg

[Eric McCammond]

Thank you Dom and Joerg.  That was very helpful.