Part of the reason is because the glass plates the images were photographed on are relatively large. The glass plate was 3inches by 9inches, meaning each image

Part of the reason is because the glass plates the images were photographed on are relatively large. The glass plate was 3inches by 9inches, meaning each image was approximately 3x3. This is somewhat larger (about 80% more area 9 sq in vs 5 sq in) than medium format film and about 8 times the size of 35mm film. While it's generally accepted that 35mm is "dead", it's still being debated whether digital has surpassed medium format. Take a look at shorpy http://www.shorpy.com/ http://www.shorpy.com/ sometime. They have medium-res scans of full glass plates (8x10, 80 sq inches) and you can see the level of detail that a large negative captures. A full scan of the plate, capturing every transition between dark and light (line pair) would surely be in the hundreds of megapixels. In fact you can see that many of these images are limited not by the resolution of the plate, but the lens technology (the corners of the images are often blurred, and lens imperfection called coma)