We combine leading pixel technology, analog readout mastery, and digitization prowess with image processing savvy and system design acumen to create some of the world’s foremost digital imaging solutions. To take full advantage of all our expertise, you need to match the proper lens to your sensor. While we do not endorse any specific lens supplier, we’ve provided a list of known lens sources and their web address, along with some basic information related to lenses and lens selection.
|Alps Electric Co., Ltd.||www.alps.com|
|Asia Optical Co., Ltd.||www.aoci.com.tw|
|Baso Percision Optics Ltd.||www.baso.com.tw|
|Foxconn Technology Group||www.foxconn.com|
|Genius Electronic Optical||www.gseo.com|
|Hitachi Maxell Ltd. (Maxell)||www.maxell.com|
|Kantatsu Co., Ltd.||www.kantatsu.co.jp|
|Kinko Optical Co., Ltd.||www.kinko-optical.com|
|Largan Precision Co., Ltd.||www.largan.com.tw|
|Marshall Electronics, Inc.||www.marshall-usa.com|
|MaxEmil Photonics Corp.||www.maxemil.com.tw|
|Nidec Copal Corp.||www.nidec-copal.com|
|Optical Short Course International, Inc.||www.oscintl.com|
|Tamron Co., Ltd.||www.tamron.co.jp|
|Xiamen Leading Optics Co., Ltd.||www.leadingoptics.com|
Lens selection basics: optical format
A lens’ format is a specification of the size of the image that the lens produces and is related to the physical size of the Aptina® image sensor solution.
Originally, the measurement of a lens’ format was related to the physical size of a piece of photographic film. Now, a lens’ format represents the diagonal size of the image sensor. But this relationship is not exact because of the differences between film and digital camera manufacturing techniques. For example, a ½-inch format lens is typically paired with an image sensor that has an 8mm diagonal, not a 12.7mm diagonal as you might expect. The table below compares an image sensor’s physical diagonal to the correct optical format.
|Optical Format||Actual Sensor Diagonal|
Lens selection basics: focal length
Focal length indicates how far behind the principal plane of a lens an image will form, as well as how much the lens magnifies the image for a given condition. A lens with a long focal length produces images far behind the lens’ principal plane. Such a lens also highly magnifies the image and narrows the field of view. A lens with a short focal length produces images just behind the lens’ principal plane with a wide field of view.
For typical imaging systems, the horizontal field of view is 35 to 45 degrees. For most applications, the relationship between a lens’ focal length, f, an image sensor’s width, w, and the lens/sensor combination’s field of view, θ, is equated as:
Eq. Field of View
where tan-1 is the trigonometric operation arc-tangent. In this equation, if w is the image sensor’s horizontal width, then θ is the camera system’s horizontal field of view. Alternatively, if w is the image sensor’s diagonal width, then θ is the camera system’s diagonal field of view.
Lens selection basics: f-number
An optical system’s f-number (which is sometimes called focal ratio, f-ratio, or relative aperture) describes the ratio between the lens’ focal length and its diameter (or aperture). It usually ranges from f/1.4 to f/8 in common digital still camera or mobile handset applications, but can be much higher, perhaps f/16 or f/32, in some photography applications. Smaller f-numbers let in more light, while larger f-numbers allow more latitude for focus. The amount of light the lens lets in is inversely proportional to the square of the f-number. This means that an f/8 lens lets in 16X less light than an f/2 lens. Some lens irises provide control over the f-number or effective lens diameter. In low-cost applications, however, the f-number is usually fixed.
Lens selection basics: picking the right lens
To match the sensor’s image-detecting ability to the lens’ image-forming ability, the size, number, and distribution of the sensor’s pixels must be compared to similar qualities in the lens’ image. In determining when such a match is optimal, two parameters must be considered: the size of the sensor’s pixels (lens resolution) and the overall size of the image-sensing array (format).
Lens resolution: If a particular image sensor contains pixels that are, for example, 2.2 microns wide, then the proper lens to use with that sensor should be able to resolve 2.2-micron-wide features in the images it forms. If the lens used cannot resolve image features as small as 2.2 microns, then the images resulting from that particular lens/sensor combination will appear to be blurry. On the other hand, if the lens used resolves image features that are equal to, or smaller than, 2.2 microns wide, then the resulting images will be sharp. This principle can be taken too far, however, when the lens used can resolve image features that are much smaller than the sensor’s pixel size.
Format: If a particular sensor array has a ¼-inch optical format (corresponding to a diagonal of approximately 4mm), for example, then the proper lens to use with it will be one that can form images at least as large as a ¼-inch format (but not much larger).