What are the f-numbers on machine vision camera lenses? f-stop explained!

machine vision lens

Why does 1stVision focus (no pun intended) so much on machine vision lenses.  As the old saying goes, if you have garbage in, you get garbage out.

The lens is the input to the machine vision system.  A low quality lens means that you have already degraded the image coming into the sensor.  For instance, let’s say you chose a camera with 5um pixels, which equates to a lens being able to resolve 100 lp/mm.  If your lens’ Modular Transform Function (MTF) is only 50 lp/mm, you should have chosen a camera with 10um pixel size, because the lens can’t do any better than that.   As a note, don’t infer that a camera with 10um pixels is worse than a camera with 5umpixels from this example, as that is not true.  Learn more on MTF here

Click hereA machine vision lens gathers light and then focuses it.  When we talk about focus, we are talking about the MTF, but when we discuss light gathering properties, we need to discuss the lens f-number.

FUJI -f-stop
FUJI lens showing f-stops
f-number
The f-number is defined as the ratio of the focal length by the aperture width (diameter of the entrance pupil).  So a 50mm focal length lens with a f-number of 2 has a 25mm entrance pupil.  The lower the f-number, the more light  will be allowed into the system, however this equates to more expensive  lens as you need more glass to make a wider entrance pupil.

f-stop
Many camera lenses have an adjustable iris that opens and closes at the front of the lens to limit the amount of light coming in.  When open all the way, the f-stop is the f-number.  From there, each f-stop from wide open halves the amount of light, which corresponds to reducing the size of the aperture by 1/sqrt(2) or about 0.707 and in turn halving the area.

f-number
Diagram of decreasing apertures, that is, increasing f-numbers, in one-stop increments; each aperture has half the light-gathering area of the previous one.

The f-stop is represented by a sequence of these numbers below, each letting in half the light.

Sequence:  f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32, f/45, f/64, f/90, f/128

The sequence is obtained by approximating the geometric sequence

s-stop sequence

Characteristics of the f-stop

  • Most lenses are designed to be optimal in the F4-F5.6 range, in which they have the best MTF.
  • The higher f-number (ie f/8 ) is, or the more closed the aperture is, better the depth of field if achieved
  • The lower the f-number (ie f/1.4) is, or the aperature being wide open is where you get the least depth of field, but not great MTF.

In a practical application, you need to trade off exposure time, depth of field, and available machine vision  lighting.  These three variables are always in tension.  If you need fast exposure AND depth of field this means very small amounts of light gets to the sensor.  If you need high contrast images in this situation, something has to change.  Either get more light, accept less depth of field, or have some image blur.

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For a full listing of machine vision lenses, click here and use the filter to help in your selection. 

1st Vision’s sales engineers have over 100 years of combined experience to assist in your camera selection.  With a large portfolio of lenses, cables, NIC card and industrial computers, we can provide a full vision solution!

Related Blog posts

Not All Lenses are Created Equal! Lens MTF Comparisons

10 key things you need to know when selecting a machine vision lens

Demystifying Lens performance specifications

Information courteous of Wikipedia

 

 

 

Learn about the new 5GigE camera interface

Dalsa Nano 5GigE

Machine vision interfaces have continued to evolve over the years increasing data throughput and cable lengths.  Commonly used interfaces are GigE and USB3.  However, 5GigE is an interface now gaining attention in the industrial imaging / machine vision market with some nice advantages.

We will outline the benefits of 5GigE, but first, lets give a brief overview of the commonly used camera interfaces, with their pluses and minuses:

GigE  / GigE Vision

  • 110 MB/s of sustainable throughput.  In real world terms, a HD, 2MP camera can get 50-55 fps in 8 bit mono or 8 bit color mode.  Note, this isn’t real HD, since you need 60 FPS.
  • Data cable lengths up to 100m using regular CAT 5e/6 cable.
  • Easy to put multiple cameras on a system.

USB 3 / USB3 Vision

  • 420 MB/s of data throughput.    A HD 2MP camera can run 60 fps in 8 bit mono or color and can  also run RGB at 60 FPS no problem.  With the higher throughput,  a 5MP camera can achieve 85 fps in 8 bit mode.
  • Data cables up to 5 meters and up to 20 meters with active cables. However, active cables can be quite costly, adding up to $200 in cost.
  • Not as easy as GigE to put multiple cameras on a system, and gets harder with each additional camera, especially if you have limited USB3 controllers.

As a note, there is no cost difference when using cameras with the same sensor from the same manufacturer with USB or GigE!  They will cost about the same with no premium for one interface over the other.

gige nano 5gigeWhat are the limitations of GigE and USB3 now solved by 5GigE?

  • USB3 is limited in cable length, so going faster than GigE is great, but you can not have long cable lengths.
  • GigE has cable lengths up to 100 meters, but is limited to ~ 110MB/s of data, so you do not have the high frame rates as in a USB3 camera.
  • USB3 in 4+ camera systems is not as stable as GigE AND you’re still limited on cable lengths.

Wait! – What about 10GigE? 

Up until now, 10G was the next interface. However, the jump to 10G has quite a few limitations as outlined below.

  • Heat generation is significant, so cameras are large and not in the smaller 29 x 29mm cube form factor.
  • Not a lot of demand for very high speed 10G, so not a lot of sensors being offered
  • Minimal number of manufacturers for 10G, higher cost.
  • Special cabling, either optical or high quality cat 7.

What we have found is that there are several types of applications for 10G cameras and are as follows

  • Applications where you need 10G of speed of course (high resolution + fast frame rates)
  • Require greater than  110MB/s of data and need long cable lengths.
  • Where there is the required combination of 110MB/s for high frame rates, multiple cameras and long cable lengths, 10G is a perfect solution.

We have seen that the need for higher bandwidth + long cable lengths is more prominent vs. the real need for 10GigE!

 Introducing 5GigE that provides increased bandwidth, long cable lengths at reasonable prices! or N Base T.5GigE machine vision applications

5GigE (also known as N Base T) has become a new standard for industrial, machine vision cameras.

In the general compute world, a much much larger market than vision, there has also been a need to go faster than GigE. However, the issue of replacing the existing cabling is the major issue preventing this. If you think of a big box store, say a Home Depot for instance, the amount of cabling is huge. Ripping that out and rewiring far exceeds the cost of the equipment to use it!

5G was made to go faster, but use existing cabling. Regular cat6e cable can be used, and 5G is a subset of 10G, so all switches etc. can be kept in service.

5G gives users in the vision market USB3 speeds, but with ALL of the regular GigE features, at a very small premium!

get quote1st Vision’s sales engineers have over 100 years of combined experience to assist in your camera selection.  With a large portfolio of lenses, cables, NIC card and industrial computers, we can provide a full vision solution!

 

What is a “TECless” SWIR camera? Learn more about Allied Vision’s highly cost-effective SWIR camera models

SWIR camera

Allied Vision Goldeye SWIR cameraShort Wave Infra-Red (SWIR) imaging is now more economical with the introduction of Allied Vision’s TECless Goldeye cameras.  SWIR cameras open up numerous application possibilities for machine vision solutions, since they are able to detect defects that are not visible to the naked eye.

SWIR cameras have an InGaAs (Indium Gallium Arsenide) sensor that detects wavelengths between 900nm and 1,700nm.  These wavelengths are invisible to the human eye and CCD / CMOS cameras, however SWIR cameras detect the invisible wavelength found in various applications.  For example water accumulations inside fruits or defects within silicon products.

SWIR - light emmission at 1150nm
Light emitted by silicon in solar cells peak at 1150nm

Learn more about applications solved with SWIR cameras HERE. 

SWIR cameras typically require Thermal Electric Coolers (TEC’s) which enable low-noise imaging in the spectral range of 900mm to 1,700nm.  Additionally, the TEC’s compensate for high temperature fluctuations and stabilizes the image sensor.
 
For temperature stable environments, Allied Vision now has a “TECless” InGaAs camera providing a lower entry price point, in turn an excellent price-performance ratio.
 
The Goldeye G-033 and CL-033 TECless InGaAs cameras are the solution to applications unachievable with standard cameras offering the following features
 
  • SWIR imaging from 900nm to 1700nm
  • High frame rates of 301 fps with VGA resolution
  • Power over Ethernet (PoE)
  • Compact design with no fan
  • Lower cost vs TEC versions
  • GigE and Camera link interfaces.

Click below for the full specifications on the Goldeye  TECless cameras and click “Get Quote” for pricing

GigE – Goldeye G-008 TECless
Camera link – Goldeye CL-008

Need to see it for yourself?  1stVision can provide a demo Goldeye camera to test on your application.  Submit your request for a demo camera by entering “Send me a demo SWIR camera” in the comment box.
 

Download the comprehensive SWIR application white paper here.  

1st Vision’s sales engineers have over 100 years of combined experience to assist in your camera selection.  With a large portfolio of lenses, cables, NIC card and industrial computers, we can provide a full vision solution!

Related Posts

How to select the best SWIR camera for my application and understand applications it can solve.

Download the comprehensive SWIR application white paper.

Learn about CoaXpress and frame rates achievable with Allied Vision’s “Bonito Pro” cameras with CXP-6

Allied Vision Bonito Pro camera

What is  CoaXPress, especially with “CXP-6” capability?

CoaXPress is an established industry standard allowing high speed communications over coaxial cable.  The current version supports bit rates up to 6.25 Gbits/sec over a single coaxial cable.  When used in parallel, two or more coaxial cables can provide incremental speed gains.  The naming convention associated with CoaXPress signify the bit rate as seen in the chart below.   In cases that you see CXP-6 has a bit rate of 6.25 Gb/s.  The 4 x means the number of lanes. Multiply the 2 and you get your total bit rate.

CXP CoaXpress

The new Allied Vision Bonito Pro cameras utilize 4 DIN 1.0/2.3 connectors on a CXP-6 interface (4 lanes) x 6.25Gbits/Sec. This  allows for resolutions of up to 26 megapixels to reach 70 frames per second (fps).  The first two Bonito PRO models (Bonito PRO X-2620 and X-1250) support high resolution with 26.6MP and 12.5MP at 80 and 142 fps respectively.

The Bonito PRO cameras are ideal for a wide range of applications including, 2D/ 3D surface inspection,  high speed printing, PCB & Electronics inspection.

Even faster frame rates can be achieved using the Bonito Pro X1250 (12.5MP) in partial scan mode.  Set to a 768 line height, a rate of 503 fps can be achieved!

Bonito Pro frame rates

The following video’s are good representations of what this relates to in real applications which you can appreciate.

Full specifications for the Allied Vision Bonito Pro cameras can be found HERE, but main features and benefits include:

  • Sensors available in Monochrome (X-1250B) and Color (X-1250C) and extended near-infrared (X1250B NIR ) models
  • On board defect pixel and 2D fixed pattern noise correction for improved image quality
  • Fan-less design for industrial imaging applications.
  • DIN 1.0 / 2.3 CoaXPress connections for secure operation in industrial environments.
  • Single cable solutions using trigger and power over CoaXPress (PoCXP)

contact us1st Vision’s sales engineers have over 100 years of combined experience to assist in your camera selection.  With a large portfolio of lenses, cables, NIC card and industrial computers, we can provide a full vision solution!

 

UPDATE:  New video of the Bonito Pro detailing the multi-ROI function