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Focal length

A lens’ purpose is to focus light very sharply at a specific point behind that lens, like a magnifying glass focusing sunlight on a piece of paper a short distance behind it.

F stopsexplained

Unfortunately, the listed focal length of a lens does not always perfectly correspond with an exact angle of view, at normal shooting distances. Many lenses change their angle of view slightly when they are focused closer than infinity, and some lenses change their angle of view by a very noticeable amount. Therefore, some photographers measure the “true” angle of view when focusing on a subject at the distances they normally shoot at, such as 5ft or 10ft from the lens.

To most photographers, the term “focal length” simply refers to a number on a lens that indicates how “wide” or “telephoto” that lens is. The higher the number, the more telephoto the lens.

focallength是什么

Focus distance

This next diagram is also inaccurate compared to the actual optical formula of the particular lens, however it depicts the general concept of a multi-element lens construction: Light may enter the first element of the lens at a very sharp angle, and “bend” to a more manageable angle as it travels through the lens. In other words, if you wanted to create an 11mm lens on a 35mm full-frame sensor, with just one piece of glass, then yes, the nodal point of that lens would need to be 11mm away from the surface of the sensor, which is impossible on many cameras, and impractical or at least sub-optimal on all cameras.

However, the term itself does correlate to a specified “length of focus”, and to understand this number we have to understand how a lens itself works, both in theory and in practice.

Focal lengthcamera

Indeed, each of the glass elements in a modern lenses will bend light in one direction or another. There are two reasons for this: first, to create a flat plane of focus instead of a curved one, and second, to create enough empty space behind the rearmost lens element to fit a shutter, and in the case of SLR cameras, a mirror.

Focaldistance vsfocal length

Of course an astute photographer will point out, those blue lines sure don’t look very wide-angle, and that lens is in fact an ultra-wide-angle zoom! Is that diagram wildly inaccurate?

Therefore, optics are used to bend light in a way that moves the nodal point forward away from the sensor, making the focal length distance purely theoretical.

focallength中文

At Coweta Tech Precision, we make high-quality CNC machined parts for all your optical industry needs. You can get machine parts of any material manufactured at our in-house shop, including aluminum, steel, Hastelloy, Delrin, Teflon, nylon, and Plexiglas. We specialize in stainless steel (300 and 400 series), employing CNC precision machining to ensure the utmost accuracy and durability.

At Coweta Tech Precision, our CNC-machined parts are meticulously crafted to meet the specific demands of the optical industry. Employing advanced CNC technology, our operations are guided by sophisticated CAD/CAM software, ensuring precision in every cut and contour. This high level of accuracy is crucial for producing optical components that surpass industry standards in both quality and performance. Our team of skilled machinists utilizes high-precision tooling to handle complex geometries, ensuring consistency and reliability in every product. This attention to detail guarantees that each component preserves its functional integrity, essential for optimal performance in optical applications. By consistently delivering such high-quality parts, we build strong confidence among our clients, making us a trusted partner for manufacturers of optical machines.

This is why, in modern photography, a listed focal length is merely used to indicate that lens’ angle of view when focused at infinity. A 50mm lens has a 46.8 degree angle of view. A 24mm lens has an 84 degree angle of view, while a 200mm lens has a 12.3mm angle of view. The two numbers are always inversely proportional.

Camera lenses, however, have multiple glass elements and an aperture iris, which are all used in conjunction to sharply project a scene onto the image sensor inside the camera.

For example, many professional 70-200mm zoom lenses, when focused at 200mm and very close distances, actually give an angle of view that is much shorter, along the lines of 105-150mm.

Accuracy is paramount in the machining of optical components with intricate geometries. At Coweta Tech Precision, our CNC optical machines are driven by state-of-the-art CAD/CAM software, meticulously optimized to maximize efficiency and minimize material waste. This meticulous approach to manufacturing optical components ensures that our clients can rely on the exceptional quality of the end products. Equipped with advanced precision tooling and CNC milling capabilities, our skilled machinists deliver products that instill confidence among designers and manufacturers of optical machines. They depend on us for the high-grade optical materials and precise micro-machining processes we employ, which are crucial for consistently achieving superior results.