<p>I just finished the film...a phenomenal documentary. Although the issue was briefly discussed in the film, I assumed it would be trivial to judge if a lens was at work by looking for barrel distortion, especially given the simple lens involved. I Googled for a while to understand what level of distortion might be introduced if a large camera obscura set-up includes a simple lens (rather than just a pinhole, which I know creates no distortion)...but came up empty. In any case, looking at the original and Jenison's art using Photoshop's lens correction tool, I see little meaningful evidence in the edge areas of distortion.<br>
Another clue that wasn't mentioned is brush strokes. Anyone painting over the edge of a mirror would probably paint primarily in small strokes parallel to the mirror's edge...has anyone explored this?<br>
Anyway, a great film.</p>