Recently, I decided to purchase an inexpensive store-bought pinhole camera to get a feel for exposure and processing. The on-line specs for the (Santa Barbara) camera I bought say that the camera has an f/154 and say: "This is a Baltic Birch, 4 x 5" Pinhole Camera, with a focal length equivalent of 50mm, which is a super wide angle lens for this format. Average exposure in bright, noon-day sun is 4 seconds, using 400 ISO film." The exposure time quoted is *much* longer for ISO 400 film than I expected after using a number of exposure calculators for these conditions, which consistently give exposures of 1/4 second or so even with correction for reciprocity failure, minimal, I guess, for such a short exposure. So why would the manufacturer suggest shutter speeds 16 times longer than the charts suggest? What am I missing here? I do realize that I will ultimately have to experiment to get this straight, but it would be great to be in the right ballpark when I start the experimentation. Thanks.