Camera Lens Focusing Flashcards
What’s happening when focus is shifting?
Despite technological advancements, the fundamental process of focusing in photography involves adjusting the position of lens groups.
How is the viewfinder like an illusion?
When looking through a camera’s viewfinder, photographers are not directly viewing through the lens but at an image projected onto a focusing screen.
What’s the origin of ground glass?
The ground glass, a basic focusing screen, is essential for accurate focusing, especially in early large-format cameras.
How did focus shifting adapt as cameras got smaller?
As photographic formats became smaller, challenges in focusing arose, leading to the exploration of alternative methods like hyper-focal and zone focusing.
What is the loupe advantage?
In large-format cameras, a loupe was often used to magnify the image on the ground glass for more precise focusing. Normally, a loupe is a necessity for almost any photographer who prints his or her own work. The pocket-size device enlarges the smallest details in your negatives and prints and comes in handy whether you are examining the quality of a print, the details of an enlargement, or the individual images on a contact sheet.
What is zone focusing?
Marking lens distances and using distance scales became a technique known as zone focusing, with limitations for fast or long lenses.
What is rangefinding?
A rangefinder (also rangefinding telemeter, depending on the context) is a device used to measure distances to remote objects. Originally optical devices used in surveying, they soon found applications in other fields, such as photography, the military, and space travel. They were especially useful for finding the range of a target, such as in naval gunnery and anti-aircraft artillery.
What is a coincident image range finder?
Cameras like Leica’s M series employed coincident image rangefinders, aligning two images in the viewfinder for accurate focusing. A coincidence rangefinder or coincidence telemeter is a type of rangefinder that uses mechanical and optical principles to allow an operator to determine the distance to a visible object. There are subtypes split-image telemeter, inverted image, or double-image telemeter with different principles how two images in a single ocular are compared.
What were some of the challenges of rangefinders?
Calibration and accuracy issues, particularly with long telephoto lenses, were challenges faced by coincident image rangefinders.
What did single lens reflex camera do?
Single-Lens Reflex (SLR) cameras revolutionized focusing by placing a focusing screen at the same distance from the lens mount as the film or sensor.
What is vernier acuity?
Exploring the concept of vernier acuity, the article emphasizes the human eye’s ability to align objects accurately. Vernier acuity measures the ability to detect a misalignment or positional offset between visual stimuli, for example between two vertical lines when reading a vernier scale.
How did split prism change the game?
The split-prism focusing aid, using prisms, introduced a new way to think about focusing, exploiting the vernier acuity principle.
What is phase detect auto focus?
PDAF (phase detection auto focus) is a high-speed automatic focus technology. PDAF in consumer cameras generally uses some of the pixels for imaging on the image sensor as pixels for phase detection. Because PDAF can quickly and accurately focus the lens for each frame it detects, it enables faster and more accurate auto focus (AF) than conventional AF. With phase detection autofocus, think a bit of the moon and its various phases. For the camera, when a specific point finds itself being in perfect focus, there are light rays.
A photograph that is in focus will have light rays that will cast a light on the opposite sides of the lens. This is when the term ‘in phase’ comes about, like how phases of the moon work. The camera can figure out when the focus is not achieved because the opposite side is no longer illuminated (known as not being in phase). This happens when the lens is not focused correctly on the point. It may be in front of or behind it. Phase detection autofocus systems extended the split-prism concept, providing accuracy and context, especially in SLR cameras.
What are hybrid autofocus systems?
Hybrid autofocus systems, combining phase detection and contrast detection, offer speed, context, and accuracy benefits, representing a modern focus solution. In a hybrid autofocus system, focus is achieved by combining two or more methods, such as: Active and passive methods. Phase detection and contrast measurement.
What is contrast-detection autofocus?
Contrast-detection autofocus is achieved by measuring contrast (vision) within a sensor field through the lens. The intensity difference between adjacent pixels of the sensor naturally increases with correct image focus. The optical system can thereby be adjusted until the maximal contrast is detected.
