Film vs digital cameras


I kind of have an understanding about film camera, but for some reason I cannot wrap my head around how digital cameras work. From a mechanical and engineering standpoint, what is the actual difference between how the two operate?

In: 2

The film camera takes light through a lens and puts it onto a strip of film. The digital camera takes light through a lens and puts it onto a hard drive so you can download it on your computer.

Photographic film uses an array of tiny light-sensitive crystals (each sensitive to a different color of light in the case of color film). More light makes the resulting image get brighter by activating the crystal more.

Digital cameras replace the crystals with an array of light-sensitive electronic elements. To record color, these elements are below a grid of colored lenses that impact the relative amount of light each element receives. Computers (either in the camera or an external computer) put the picture together based on the recorded amount of light each element received and make a best-guess at the color (called demosaicing and interpolation) based on each element’s position in the color grid. Most cameras use what is called a Bayer filter (but there are other configurations as well) so the process is also sometimes called De-Bayering.

Functionally there’s not much of a difference between film and digital in terms of optics. There isn’t much of a reason a 40-year old 35mm SLR couldn’t be retrofitted to be a digital camera if you wanted to badly enough. Things like Digital Backs were a thing a decade or so ago so you could make a Cannon AE1 or a Nikon F3 digital.

Technically a digital camera uses a CCD or CMOS chip with a pixal array which is light sensitive to capture an image where it captures the image one row at a time. There are two different types of shutters that can be used (in logic), a Rolling shutter, which captures the image one row at a time, and a global shutter, where the image is captured all pixels at once, but it’s still read one line at a time. Rolling Shutters produce excellent images on static and slow moving objects, but get distortion on high speed objects, Global shutters are used for capturing high-speed objects.

On-board computers process the data into a usable image format.

In regards to how the light enters the camera and reaches the light sensitive film/sensor there is no difference between how digital and film cameras work.

The only real difference is a digital camera has a light sensor instead of light sensitive film.

A digital sensor has an array of light sensitive photosites. When the shutter is open these count the photons falling on them. The more photons the brighter that pixel will be in the resultant image. The photosites are covered in a colour filter. Each individual photosite receives red, green, or blue light depending on the colour of the filter above it. The software that converts the recorded signal into a picture uses clever maths to produce a full colour image at each pixel.

The optical part is mostly the same, the difference is that instead of light hitting film and causing a chemical reaction, it hits an image sensor, which is basically a bunch of light sensitive diodes(like solar cells, which are also fundamentally just diodes), The signal from light hitting the diode gets amplified, and converted from an analog voltage or quantity of charge into a digital format using an ADC.

The light sensing happens when a photon interacts with an electron, pushing it across the PN junction.