Focussing on the Obscura 50 Optic

[John Fontana]

Am I right in thinking that when a 50 mm Obscura optic is fitted to the Composer Pro, the focussing ring is virtually obsolete. Using depth of field tables, with a subject distance at 5 metres at f32, near focussing distance to far focussing distance is about 1.7 metres to infinity, at f64 1 metre to infinity, and at f161 about 0.5 metres to infinity. The blurring effect of the zone plate and sieve add to focussing being immaterial using the Obscura

 

[f2bthere]

You are correct. Pinholes are not focused. They are to be set at the correct “focal length“ they were designed for. In the Composers, this is the infinity focus position.