Focussing on the Obscura 50 Optic

John Fontana

TPF Noob!
Jun 4, 2019
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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
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.

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