Difference between revisions of "Cameras, lenses and mirrors"

Latest revision as of 15:56, 28 January 2016

IMPORTANT NOTES

Never touch the sensor element (CCD or CMOS) of a camera with anything! It can very easily be scratched.

Never touch the glass elements of a lens with your hands! The oil from human skin will cause damage.

Cameras

In the AIRLab you can find different kind of cameras. These are the main groups:

• Analogue cameras. Video output is given as an electrical signal, which needs analogue-to-digital conversion to be processed by a computer; this is done by a specific card called frame grabber or video capture card (the latter tend to be the lowest-performance items; see Cameras, lenses and mirrors#Frame grabbers for details). Analogue video is outdated for computer vision and robotics applications, due to its cost, low performance and complexity; nowadays digital camera systems (such as all the ones listed below) are always preferred.
• USB cameras. Usually very cheap, they are suitable for low-performance applications (i.e. those where low frame rate is needed and low image quality can be accepted). Their main advantage (along with cost) is the fact that every modern computer has USB ports. The fact that the USB standard includes 5V DC power supply lines helps simplifying camera design and use.
• FireWire cameras. The FireWire (or IEEE1394) bus is generally used for low-end industrial cameras, i.e. devices with technical characteristics much superior to those typical of USB cameras but low-performance according to typical machine vision standards. Industrial cameras usually give to the user a much wider control over the acquisition parameters compared to consumer cameras, and therefore they are usually preferred in robotics; their downside is the higher cost. There are different versions of IEE1394 link (see http://en.wikipedia.org/wiki/Firewire for details), with different bitrates, starting from the 400Mbit/s FireWire 400. Generally they are all considered superior to USB 2.0, even if theoretical bandwidth is lower for FireWire 400. Firewire ports can include power supply lines, but some interfaces (and in particular those on portable computers) omit them. Although the use of FireWire interfaces has expanded in recent years, they are not yet considered a standard feature for motherboards.
• GigE Vision cameras. GigE Vision (or Gigabit Ethernet Vision) is a rather new connection standard for machine vision, based upon the established Ethernet protocol in its Gigabit (i.e. 1000Mbps) version. It is very interesting, as complex multiple-camera systems can be easily built using existing (Gigabit) Ethernet hardware, such as cables and switches. Vision data is acquired simply through a generic Ethernet port, commonly found on motherboards or easily added. However, 100Mbps (or fast Ethernet) ports are not guaranteed to work and can sustain only modest video streams; on the other hand, 1000Mbps ports are now standard on motherboards, so this will not be a problem anymore in a few years. It seems that GigE Vision is becoming the most common interface for low- to medium-performance industrial cameras.
• CameraLink cameras. Cameralink is a high-speed interface expressly developed for high-performance machine vision applications. It is a point-to-point link, i.e. a CameraLink connection is used to connect a single camera to a digital acquisition card (frame grabber). Its diffusion is limited to applications where extreme frame rates and resolutions are needed, because CameraLink gear is very expensive.
• ST Camera boards. Cameras with cell phone sensor and ARM processor for onboard computation.
• Pixy Is a fast vision sensor that can be quickly “teached” to find objects, and it connects directly to Arduino and other controllers. Pixy processes images from the image sensor and only sends the useful information (e.g. purple dinosaur detected at x=54, y=103) to the microcontroller. The information is available through one of several interfaces: UART serial, SPI, I2C, digital out, or analog out. So Arduino or other microcontroller can talk easily with Pixy and still have plenty of CPU available for other tasks. (For more details see: Official web site and the web page that contains all the drives and guides: Project info)

The following is a list of the cameras available in the AIRLab. (To be precise, it is a list of the cameras that are modern enough to be useful.) For each of them the main specifications (and a link to the full specifications) are given. Details on the different types of lens mount are given below in Cameras, lenses and mirrors#Lenses. The 'how many?' field tells if multiple, identical items are available. Finally, the 'where?' field tells you in which of the AIRLab sites (listed in The Labs) you can find an item, and the 'project' field is used to specify which project (if any) is using it.

Ah, one last thing. People like to actually find things when they look for them, so don't forget to update the table when you move something away from its current location. If you don't know where you are taking it, just put your name in the table.

List of Cameras

Lenses

Be aware that sensor dimension (i.e. its diagonal, measured in fractions of an inch) is not the same for all cameras. Therefore one of the key specifications for a lens is the maximum sensor dimension supported. If you use a given lens with too big a sensor, the edges of the image will be black as they lie outside the circle of the projected image. Also beware of the strange convention used for sensor diagonals, i.e. a fraction in the form A/B" where A and B are integer or non-integer numbers. For instance an 1/2" sensor is smaller than an 1/1.8" one. The variability of sensor dimensions has another side effect: the same lens has a different angle of view if you change the sensor size. Therefore the same lens can behave as a wide-angle with a large sensor and as a telephoto with a small sensor.

An useful guide to lenses (in Italian or English) can be found at http://www.rapitron.it/guidaob.htm.

The following is a list of the actual lenses available in the AIRLab. For each of them the main specifications (and a link to the maker's or vendor's page for full specifications) are given. A '?' means an unknown parameter: if you know its value or experimentally find out it when using the lens (e.g. the maximum sensor size), please update the table before the information is lost again! Lenses having 'M12x0.5' in Column 'mount type' are only usable with Unibrain's Fire-i board cameras. A 'YES' in the 'Mpixel' column indicates a so-called Megapixel lens, i.e. a high quality, low-distortion lens designed for high-resolution industrial cameras (typically having large sensors); please note that some of these are specifically designed for B/W (i.e. black and white) cameras. The 'how many?' field tells if multiple, identical items are available. Finally, the 'where?' field tells you in which of the AIRLab sites (listed in The Labs) you can find an item, and the 'project' field is used to specify which project (if any) is using it.

Ah, one last thing. People like to actually find things when they look for them, so don't forget to update the table when you move something away from its current location. If you don't know where you are bringing it, just put your name in the table.

C-mount and CS-mount lenses

Industrial cameras usually have interchangeable lenses. This allows for the choice of the lens that is more suitable to the considered application. There are two main standards for industrial camera lenses: C-mount and CS-mount. Both are screw-type mounts.

CS-mount is simply a modified C-mount where the distance between the back of the lens and the sensor element (CCD or CMOS) is shorter, as CS-mount lenses have a shorter focal distance. Precisely, the mounting flange (i.e., the threaded hole for the lens) of a CS-mount camera is 5 mm nearer to the sensor than the mounting flange of a C-mount camera. As a consequence, the part of a CS-mount lenses that stays between flange and sensor must be physically shorter than the corresponding part of a C-mount lens.

This means that a C-mount lens can be mounted on a CS-mount camera, but only if you use an "adapter ring". An adapter ring is a distancing cylinder with suitable threads that provides +5 mm of additional distance between lens and camera. (Do not mount the lens on the camera without the adapter ring! You will break the sensor, scratch the lens, or both.)

On the other hand, a CS-mount lens on a C-mount camera will not work correctly (but trying should not damage anything).

M12 lenses

We also use M12 lenses. These lenses are very simple, with no iris, and very small. Their mounting system is an M12x0.5 metric screw thread. They are commonly used for webcams, and usually do not provide the top optical quality.

Frame grabbers

As previously said, a frame grabber is an electronic board that connects to one or more cameras, and converts the signals from the cameras into a data stream that can be elaborated by a computer. They are usually designed as expansion boards to be fitted into the computer case. Frame grabbers are necessary for analogue cameras (as they include the analogue/digital converters) or for CameraLink digital cameras (in this case the frame grabber is essentially a high speed dedicated digital interface). Other kinds of digital cameras don't need a frame grabber: this is one of the main advantages of digital cameras over analogue ones in machine vision applications, where the processing is almost always performed by computers. In the AIRLab two models of frame grabber are available:

• a digital frame grabber from Euresys, model Expert 2, having two CameraLink inputs (http://www.euresys.com/Products/grablink/GrablinkSeries.asp). Notes: needs a PCI-X slot; one of the inputs is not working due to a fault.
• two multichannel analogue frame grabbers from Matrox, model Meteor II/Multi-Channel, having three analogue inputs that can be combined into a single three-channel RGB analogue input (http://www.matrox.com/imaging/support/old_products/home.cfm). Note: one item is permanently mounted on the MO.RO.1 robot: see The MO.RO. family for details.
• two multichannel analogue frame grabbers from Matrox, model Meteor II/Multi-Channel, having three analogue inputs that can be combined into a single three-channel RGB analogue input (http://www.matrox.com/imaging/support/old_products/home.cfm). Note: one item is permanently mounted on the MO.RO.1 robot: see The MO.RO. family for details.
• two single-channel analogue frame grabbers from Matrox, models Meteor and Meteor Pro (http://www.matrox.com/imaging/support/old_products/home.cfm).

All the frame grabbers (except the one on the MO.RO.1) are currently in AIRLab/DEI. If you move one of them, please write it down here... and do it NOW!

Mirrors

Much work has been done and is being done at the AIRLab on the topic of omnidirectional (machine) vision (sometimes referred to as omnivision). Omnidirectional vision systems use special hardware to overcome the limitations of conventional vision systems in terms of field of view. The approach to this problem that we generally adopt is the use of conventional cameras in association with convex mirrors, i.e. the capturing of the image reflected by a suitably-shaped mirror with a camera. The possibility of designing mirrors with specific geometric properties gives a very useful means to control the geometric behaviour of the whole camera+mirror system.

TODO for someone who knows better ;-) : mirror list

Cable

The complete list of cable for camera connection and/or power is under construction. You can partecipate listing below which cables are you using...