Imaging Theory

Taking pictures is a fun process, but you have to learn some theory and physics to understand the magic of light. This chapter will describe main concepts (like focal length and aperture) briefly and help you to get more good pictures.

Since our primary business is making adapters, the first question to consider is:

Do lens adapters affect image quality?

Now, what is the camera lens at all?

A camera lens is an optical component used in cameras to focus and capture images. It is one of the most critical parts of a camera system, as it plays a crucial role in determining the quality and characteristics of the photographs taken.

Here are some key points about camera lenses:

Optical Elements: A camera lens typically consists of multiple optical elements, including glass or specialized materials. These elements are designed to bend and manipulate light rays in a way that allows the camera to focus on a subject and form a sharp image on the camera's image sensor or film.
Focal Length: The focal length of a lens is one of its most important characteristics. It determines the lens's field of view and how objects are magnified in the resulting image. Lenses can have fixed focal lengths (prime lenses) or variable focal lengths (zoom lenses).
Relative Aperture: The aperture of a lens controls the amount of light that enters the camera. It is represented as an f-number (e.g., f/2.8, f/1.4) and influences factors like depth of field and low-light performance. A lower f-number (e.g., f/1.8) means a wider aperture, allowing more light to enter.
Zoom and Prime Lenses: Zoom lenses have variable focal lengths and can zoom in or out to change the composition of a shot. Prime lenses have a fixed focal length and often offer better image quality and wider apertures.
Specialized Lenses: Some lenses are designed for specific purposes, such as macro lenses for close-up photography, fisheye lenses for extreme wide-angle views, and tilt-shift lenses for perspective control.
Lens Mount: Lenses are attached to a camera body using a specific lens mount, ensuring compatibility between the lens and camera. Different camera manufacturers have their own proprietary lens mounts.

Different lenses provide an image of different quality. Some parameters affecting this are:

Brightness Distribution - how much brighter the image is in the frame center compared to the frame edge
Light Scattering - multiple reflections from glass surfaces, their faces, and inner parts of the lens housing, that causes additional unwanted lighting of objects
Light Transmission - the percentage of light that passes through a lens and reaches the camera sensor or eyepiece. This refers not just to the amount of light energy transmitted through the optics, but also color accuracy, vignetting and aberrations
Resolution - the ability of the lens to register tiny details separately (may be limited by a film or a digital sensor resolution, actually)

If you think about adapting a lens to your camera, there are a few more things to consider:

Back Focal Length - the distance between the lens rearmost glass element and camera sensor when the lens is focused to infinity. If you can't place the lens close enough to the sensor, you will be able to take close-ups or macro shots only.
Flange Focal Distance (FDD) - the distance from the mounting flange to the film or image sensor plane. This value is different for different camera systems. This is important for correct focusing. Also, this determines if adaptation is possible without additional optics. A simple non-optical adapter holds the longer FFD lens the appropriate additional distance away from the sensor on the shorter FFD camera. A camera body with a shorter FFD can accept a larger number of lenses (those with a longer FFD) by using a simple adapter. A lens with a longer FFD can be more readily adapted to a larger number of camera bodies (those with a shorter FFD). If the difference is small, other factors such as the sizes and positions of the mounting flanges will influence whether a lens can be adapted without optics. You can find an example of adaptation possibility analysis at the Building an adapter article.