Without understanding the principles of light and how they correlate to small apertures, pinhole cameras can seem almost like magic in the way they capture a relatively sharp image without a lens. Even with a lens you need an adjustable aperture in order to control depth of field. In the short video by MinutePhysics, they briefly explain how pinholes, lenses and apertures work.
How to See Without Glasses
In How to See Without Glasses, Henry Reich demonstrates a technique making a pinhole with your fingers to see at greater distances; the same way we stop down a lens to increase the depth of field. Lenses like the ones on our cameras and in our eyes can only focus light at a particular distance away – any further, they get blurred and create that much loved bokeh.
Unlike lenses, pinholes use the reduction of light to focus instead of relying on optics. The reduction of light causes light to focus at one particular point from any distance. This is what happens when we close down the aperture in our lens; we prevent the stray points of light from defocusing our images.
What the video fails to mention is that at a certain threshold, reducing the aperture can help create tack sharp images; move past that threshold and you enter in the world of defraction. Light, being the wave that it is, will bend and spread around the edge of an object causing banding and spectrum change. What that means for us photographers is that it will make our once sharp image blurry.
If you leave your lens fully open all the time, you will get very shallow depth of field, but sacrifice sharpness. For maximum sharpness, it is recommended to stop your lens. Anything between f/4 and f/8 will create sharp images. Smaller apertures below f/22 for full frame and f/16 for APS-C will cause light to defract and make your images soft.
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