You don't risk "overexposing" (as the article says) anything with film/paper; basically you reach the "reciprocity failure" where the rule of exposure fails, an

You don't risk "overexposing" (as the article says) anything with film/paper; basically you reach the "reciprocity failure" where the rule of exposure fails, and you can pretty much ignore the exposure time /completely/ at that point. Double it? fine. 4 times? still fine :-) I've done many 30 minutes+ exposures on both pinhole and large format cameras. On the later, it captures an insane amount of tonalities from what you are imaging, almost like "HDR" but well, with just a piece of carboard for shutter and a watch to time how long your patience lasts :-)