Looking into the Lens

Back in the 50’s and 60’s families relied on their cameras to capture special moments. The popular camera of choice was not today’s ever-present smartphone, or the sleek digital camera of today. It was the Kodak Brownie and it held a place of honor at family gatherings and was not to be left home at vacation time.

Everyone would line up to be arranged by Mom so Dad could look through the viewfinder and make sure the scene was picture perfect. At the say cheese prompt, smiles spread across everyone’s faces and all eyes would look into the camera’s big glass eye.

My childhood vision of a lens as the camera’s eye was not far off base. In the center of the eye is the pupil which dilates to admit light on the retina, allowing us to focus. In the center of the lens is the aperture which opens to admit light, in the day of the brownie, to the film plane.


The ensuing technology has taken film out of the picture. No longer is there the horror of coming upon the photo shot of a lifetime only to discover we’ve run out of film.

 Today’s cameras have a life time supply of “built-in film - image sensors.But it is still falls to the lens to perform that first and crucial step of directing the path of light rays to project the image on the digital sensor.
In discussing lenses, there are several terms to be defined. The first is…..

Field of View

Field of view is the area we are covering and the degree of detail we desire. Since it depends on two factors, the focal length of the lens and the physical size of sensor, the field of view is not a fixed characteristic of a lens and can only be stated if the size of the sensor, with which it is used, is known.
Focal Length
The focal length is expressed in millimeters (mm) and determines the magnification of the image projected onto the sensor; the higher the number the higher the magnification. Thus we would select a longer focal length for a subject farther away. The focal length is also linked to the angle of view. Using a higher focal length would narrow the field of view. Conversely, for objects closer to the camera and needing less magnification we would choose a shorter focal length giving us a wider angle of view.

Angle of View
Lenses are also identified by their angle of view. Taking into account the sensor size and the length of its diagonal, a lens is:

·         Normal – if the angle of view is about 50 degrees and its focal length equal to the diagonal measure of the sensor

·         Wide-angle – if the angle of view is wider than 60 degrees and the focal length is shorter than normal. Used for close-up objects

·         Long-focus – if it’s focal length is longer than the diagonal measure of the sensor. Used for objects farther away

·         Telephoto – the most common type of long focus lens, using special optical configurations to make the lens shorter than its focal length

F-number
Another term we use in selecting a lens is the f-number. This refers to the maximum aperture or opening of a lens and determines how much light can pass through the lens, thus affecting the intensity of the light that will hit the image sensor. The f-number is also known as the focal ratio and is calculated by dividing the focal length by the aperture.
A smaller f-number correlates with a wider aperture and since a wider aperture admits more light, it also allows a faster shutter speed.  Lens with a smaller f-number would be the best choice in an area of low light. Conversely, a larger f-number pertains to a narrower aperture, letting in less light, thus needing a slower shutter speed. A higher f-number will increase the depth of field.

Lens Footnotes
We cannot leave the topic of lenses without mentioning a couple of other factors that will be explored in more detail in a future post:

Image Sensor Size
As stated above, the relationship of the sensor size to the focal length of the lens is one of the determinants of the field of view. If replacing a lens on a camera, we must make sure the new lens is compatible with the camera’s image sensor. If a lens is made for a smaller sensor the resulting image will have black corners; and if the lens is made for a larger sensor the resulting field of view will shrink since part of the information will be “lost” outside the sensor.

Megapixel Lens
 If we are working with a megapixel IP camera, we want to take advantage of its high resolution so choosing a high quality lens is vital.  Megapixel sensors have smaller pixels so if we want frames with   crisp images from edge to edge, the resolution of the lens must match the resolution of the camera.

One More Lens Footnote
Interestingly enough (according to Wikipedia) lens derives its name from lentil since a double convex lens is the same shape as a lentil.

        

If you have any questions about IP cameras and the best type of lens for your application, Kintronics sales engineers will be glad to assist you. Call us at 800-431-1658 or use our contact form to request information.

Image Sensors – CMOS or CCD?

In a previous post we spoke about HD, IP, IR, POE, PTZ, theABC’s of IP cameras. But there are also C’s, as in CCD and CMOS. 

 CCD stands for Charge Coupled Device, and CMOS stands for Complimentary Metal Oxide Semiconductor. Both are image sensors that are used in IP cameras.  In pre-digital days a lens gathered light and focused it on film. In today’s world image sensors have taken the place of film. 

An image sensor is a silicon chip on whose surface is embedded millions of photosensitive diodes called photosites. Photosites collect light in the form of photons. The more light that hits a photosite, the more photons it records, thus photosites that hold light from highlights in the scene will have many photons while those  recording light from shadows will have few. 

 Each photosite will eventually contribute a single pixel to the image but first the sensor has to convert the photons into an electrical signal. Both CCD and CMOS perform this process but each does it in a different manner

·         CCD:  The first row of pixels is transported to a corner of the chip called a read-out register, then on to an amplifier, and finally to a digital converter where each pixel receives a digital value. Upon completion, the charge of the row is deleted and the row above it drops down to undergo the same procedure, to be replaced by the next and the next until all the pixels have been converted. When we say charge coupled device, charge coupled refers to the manner in which each row is coupled to the one above it.

·       

              CMOS    Each pixel in a CMOS chip is surrounded by several transistors that amplify and move its charge using traditional wires therefore allowing each pixel to be read individually. CMOS stands for complementary metal oxide semiconductor and refers to the process by which the chip is manufactured, with the circuits and diodes etched into its surface.This is the same process used to make computer processors and memory chips.

While CCD sensors and CMOS sensors perform the same function, the different processes by which these sensors are manufactured result in a few differences affecting both the cost and the image.  

Cost

CCD sensors are more expensive because the manufacturing process is specialized and expensive and can only be used to make CCD’s. 

CMOS sensors, on the other hand, are made using the common high yield process used for semi-conductors and memory chips all over the world.

 Mass manufacture on the same equipment cuts the cost of producing CMOS chips dramatically and spreads the fixed costs of the plant over a much larger number of devices. Costs are lowered even more because CMOS image sensors can have processing circuits created on the same chip whereas on CCD’s these processing circuits must be on separate chips.

Image

CCD sensors produce a higher quality image because they transport the charge across the chip without any distortion resulting in a minimum of digital noise.    

CMOS sensors tend to be more perceptible to noise plus the proximity of each pixel to several transistors results in photons hitting the transistors instead of the photosite, thus lowering light sensitivity. 

How big is a pixel?

It is not until the very end of digital conversion that a pixel can be said to have size or dimension. Each photosite on the image sensor has size and dimension, but the pixels themselves are just photons.

Even after they have been converted to electrical charges they lack size and shape. Think of the static charge you pick up when walking across a carpet on a dry w inter day. Can you see or measure it? And once it has been converted to digital code, it is but a series of zeros and ones. Think of your birth date or phone number. Can you give it a size or a shape?

No, a pixel must wait for the device that prints or displays the pixel before it takes on size and shape.  To do this a computer divides the screen or printed page into a grid of pixels. It then uses the values stored in the digital code to specify the brightness and color of each pixel in this grid. Think of painting by number.

 




 
How big is a sensor?

This is tricky as well. Think of standard resolution; let’s take XGA, which is defined by the width and height dimensions in pixels, or 1024x768. A sensor’s size is specified in this manner but since a captured pixel has no physical size, the sensor size is expressed in the number of photosites on its surface. However, this can be a virtual approximation of the number of pixels since in most cases each photosite will capture one pixel.

When it comes to determining what type of camera fits your needs it is not so much a question of CCD or CMOS but of resolution. And it is here that the size of the sensor and the total number of pixels comes into play. And that is a matter we will address in our next post.  

 But if you need to know now, call us at 800-431-1658 or use our contact form to request information.

IP or IP?

I thought I knew what IP stood for. Internet Protocol as in Kintronics, the IP Camera experts.  But last week I came across another IP on Twitter and when I clicked on it, the tweet made no sense. It brought my mental gears to a blinding halt.  Did I know exactly what Internet protocol is?

Protocol

I know what internet is, but what is protocol? According to Dictionary.com, protocol is

1. 1. The customs and regulations dealing with diplomatic formality, precedence, and etiquette
2. 2.   An original draft, minute, or record from which a document, especially,   a treaty, is prepared.
3. 3.   A supplementary international agreement
4. 4.   An agreement between states
5. 5.   An annex to an agreement giving data relating to it.

None of these definitions seems to really fit so I delve a little deeper and find that network protocol is defined as rules and conventions for communication between network devices.Looking at it this way #1 fits if we substitute technocratic for diplomatic.

 Internet Protocol specifies formatting rules pertaining to how data is packaged into messages to be sent or received. Internet Protocol also includes mechanisms for devices to identify and make connections with each other.  This brings me to another IP – IP address.

IP Address

 The IP address is a numerical address assigned to a specific device on a computer network. IP addresses are expressed as binary numbers but stored in text files and displayed in human language such as 172.16.2541.1. An IP address serves two functions. It identifies the host or network interface and addresses the device’s specific location.  

·        

 Or to put it succinctly an IP address points out

·         Where it is

·         How to get there

 

 IP Camera

 Each IP camera is connected to the network and has a unique IP address.  This is a stand-alone computer device that allows a user to view live, full motion video from anywhere on a computer network, even over the Internet, using a standard web-browser.  When you install IP cameras the first thing you have to do is set the IP address.   

The Other IP

I found out it stands for Intellectual Property.

 Intellectual Property covers a lot of ground. No pun intended. (If I were making a pun I’d say a lot of acres) Intellectual property refers to inventions, literary and artistic works, or to put it another way, creations of the mind. Names, images, and designs used in commerce are included.
This type of IP can be divided into two categories: 

Industrial property

·         inventions (patents),

·         trademarks,

·         industrial designs

·         geographic indications of source;

Copyright,

Literary Works – novels, poems, plays, films
Artistic Works - drawings, paintings, photographs, sculptures, architectural designs
Musical Works

Rights related to copyright include those of performing artists in their performances, producers of phonograms in their recordings, and those of broadcasters in their radio and television program. This was the issue at the heart of the storm of opposing arguments regarding the legislative bills known as SOPA (Stop Piracy Online Act in the House of Representatives) and PIPA (Protect IP Act in the Senate) which seek to fight against foreign websites that infringe on copyrighted material.
So now you know. Kintronics is not the place to come for an idea for a sitcom, but we’re still the place to come to for assistance in designing your IPcamera systems to fit your needs. Contact us at www.kintronics.comhttp://www.kintronics.com/ or 800-431-1658 or 914-944-3425.