Rooms with large windows get more light than those with small slits for a window. Similarly cameras with small aperture lenses collect less light than those with larger apertures. Another artifact that small openings give is not usually visible with the naked eye. You may think of light as traveling in straight lines, but it is actually a wave. Where that becomes visible is at the edges of the windows: it can bend slightly around windows, making edges look fuzzy. This is called diffraction. The same thing happens in photos: edges of things become slightly fuzzy. Diffraction limits the resolution of your photo, sometimes more than pixel size. In order to keep this as clear as possible, I’ll not describe apertures by f numbers, but by the actual diameter of the part of the lens which is collecting light.
Here I compare images taken with a phone camera and a bridge camera. The phone camera used a lens aperture of 12 mm. I used that to take the street photo of a lemonade vendor in Puri. That image came as a 9248 pixels wide jpeg (all photos are in 4:3 aspect ratio) which I’ve compressed to 1250 pixels wide in the featured photo. (I think the red is too bright, but sensors have a problem with red. That’s a topic for a different post.) The bridge camera used an aperture of 62.5 mm and gave me the photo of the dragonfly as a jpeg which was 4608 pixels wide. I reduced it to 640 pixels in the view above.
Here is a zoomed in view of the two photos. In both of them I’ve selected a part of the photo 1662 pixels wide, and reduced them to 640 pixels for use here. In the photo of the dragonfly I can begin to see noise in the background; it was a very gloomy day and the photo was taken during a monsoon shower. But the edges look pretty sharp. In particular the veins in the dragonfly’s wing are quite clear. In the photo of the cart I can see that different colours are beginning to bleed into each other at the edges.
Finally, here is a zoom into a section of the originals which is 834 pixels wide. The images are reduced to 640 pixels wide for use here. I can see aliasing artifacts in the handle of the bucket: the straight line of the edge looks like a jagged lightning bolt if you look closely. There is no such artifact in the other photo. The veins on the dragonfly’s wings are still pretty sharp, but the joints between planks in the body of the wooden cart look soft. This is the diffraction limit on the resolution beginning to show. Software corrects for it, but that creates other artifacts. The bottom line? You can’t use the 64 million pixels of the phone image to zoom in a far as you can with the 16 million pixels of the bridge camera.
Phone photography changes our expectation of the interaction of camera hardware and image so dramatically that it is worth rethinking what photography means. I intend to explore this a bit in this series.