Author: Jon Chouinard

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Not All Lenses are Created Equal! Lens MTF Comparisons

In our previous blog, Demystifying lens specs,  we discussed the Modulation Transfer Function, also known as MTF, which gives you the performance of light through a medium.  The MTF helps us understand lens characteristics, however it is extremely hard to compare using manufacturer’s data sheets.  In essence, looking at a 25mm / f1.4 lens from vendor A to vendor B may look similar with basic information, but they are not!  Not all lenses are created equal and in turn need extensive data for comparison. 

The problem with comparing lens MTFs.

The problem is that most lens manufacturers DO NOT supply MTF information, or do not supply complete MTFs. Lens manufacturers with high quality optics, such as Schneider Optics, are one of the few that provide a complete set of MTFs vs. transmission.  (See an example on Pg 2 on this datasheet.)  Many will provide basic information in terms of line pairs/mm (lp/mm) measured in the center of the lens, however this is still not enough for a true comparison.  MTF data will vary with aperture (f3), light intensity and distance from the center to edges.  In turn, if you are not comparing “apples to apples”, you cannot draw a conclusion on which is the better lens.

Can I just measure the MTF myself?

The short answer to this is: Not so easily! First off, the MTF of a computer monitor is probably around 30 lp/mm. All the lenses we are discussing in this blog are at least 2x this, if not 3 or 4x it. So the limiting factor is the monitor, and you will not be able to see any differences. If you have a resolution chart, and some software where you can get the actual pixel data and plot it vs. the test pattern, you can get a better idea. However, a fairly rigid test set up with constant lighting, constant exact FOV and other identical parameters is required. This is a very lengthy process and requires special equipment. True optical testing is the correct way to determine and compare MTF.

Bottom Line:  1st Vision has done extensive testing on many lenses and have true comparisons.  We can help you determine which lens is the best for your application!…. Unless you have some nice optical equipment and some time!
Contact us to discuss the application and we can help make a recommendation!  1st Vision has 100’s of lenses in stock for same day delivery!


 Our lens webpage also highlights the resolution and distortion BUT again does not tell the whole story!

www.1stvision.com  
Ph:  978-474-0044

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Imaging Basics: How to Calculate Resolution for Machine Vision

 

 


 

 
Camera image resolution is defined by the number of pixels in a given CCD or CMOS sensor array.  This will be identified in a camera data sheet and shown as the number of pixels in the X and Y axis (i.e 1600 x 1200 pixels). 
The application will determine how many pixels are required in order to identify a desired feature accurately.  This also assumes you have a perfect lens that is not limiting resolving the pixel (see Demystifying lens specifications).  In general more pixels is better and will provide better accuracy and repeatability.  
 
 If for example you have a dark hole on a white background filling your field of view (FOV) by 90%, you will have many pixels across the feature.  On the contrary, if we have a small pin hole that is within the same field of view, we may not have enough pixels across the hole to identify the feature.  In order to find an edge you need at a minimum of 2 pixels given excellent contrast.  In order to be robust you ideally will want 3-4 pixels across a edge or feature.  
This leads us to identifying the resolution required given the size of a feature.  We will do this with an example and provide the needed formulas on how to calculate the resolution.
Example:  The vision inspection is to locate a pin hole which is 0.25mm in diameter on a part which is 20mm square.  In order to compensate for any misplacement of the part, we will set our FOV to 40mm x 30mm.  We would also like to have a minimum of 4 pixels across the 0.25mm feature.  

We can calculate the resolution required as follows:

Where:

Rs is the spatial resolution (maybe either X or Y)
FOV is the field of view dimensions (mm)  in either X or Y
Ri is the image sensor resolution; number of pixels in a row (X dimension) or column (Y dimension)
Rf is the feature resolution (smallest feature that must be reliably resolved) in physical units (mm)
Fp is the number of desired pixels that will span a feature of minimum size.

For this case we know: 

FOV(x) =  40mm
Rf = 0.25mm
Fp = 4 pixels

Calculating the spatial resolution (Rs) needed:
Rs = Rf / Fp = 0.25mm / 4 pixels = 0.0625mm pixel

From the spatial resolution (Rs) and the field of view (FOV), we can determine the image resolution (Ri) required (we have only calculated for the x-axis) using this calculation:

Ri = FOV / Rs = 40mm / 0.0625 mm/pixel = 640 pixels

We have now determined that we need a minimum resolution of 640 pixels in the x-axis to provide 4 pixels across our feature that is 0.25mm in diameter. The camera resolution can now be selected!  In today’s world, we could select a VGA (640 x 480) camera for the application.  As a note, the number of pixels required depends on many aspects of lighting, optics and algorithms used for processing.  This calculation method assumes optimum conditions.     

If you do not like math, you can download our resolution calculator here and just enter the data.  This makes it easy to test various iterations.  Download the calculator HERE. 

If you visit our camera page, you can sort by resolution in X and Y resolutions to quickly ID cameras that meet your resolution needs. 

For all your imaging needs, you can visit www.1stvision or contact us! to discuss your application in further detail or receive a quote on a desired camera.  We can also help identify which sensor is best based on the imaging conditions.  
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Low Cost imaging solutions starting @ $120 address remote focus and zoom up to 5MP

Industrial imaging applications ranging from medical and process monitoring to security and kiosks need cameras with highly functional lens control. Solutions need to be easily integrated and have the ability to remotely control the camera focus, zoom and light exposure. Depending upon the application, there are several solutions which are highlighted in this blog to satisfy a large range of applications.

 

Economical Solution  –  Feature rich

IDS’s Tiny XS 
IDS’s XS camera is perfect for applications requiring economical solutions which are small in size, lightweight requiring auto focus, automatic gain and remote digital zoom capabilities. Equipped with Aptina’s 5 Megapixel CMOS Sensor, the camera delivers excellent image quality and color reproduction.  Using the IDS Cockpit software, this camera sets up in minutes via a USB2.0 interface. 


Key Features:

  • Auto focus using a high resolution sensor (2592 x 1944 pixels)
  • Automatic Gain for varying lighting conditions
  • Remote Digital Zoom capabilities
  • Impressive video capture (5MP @ 15 fps) or higher frame rates with reduced resolution
  • Small, Light Weight – only 12 g and measuring 23×26.5×21.5 mm the XS is perfect for even the tiniest spaces.
  • Full manual control for all features available through the IDS free SDK which includes programming examples 
Want additional information?  Full Datasheets, manual and software can be found HERE

 

Low cost starting @ $120

IDS Video Class “Industrial Web Camera” – UV-1551LE

The IDS UV-1552LE-C USB Video Class camera uses a standard UVC driver with easy plug and play installation. Starting at $120 in volume, this camera is well suited where cost is most important.  No special drivers are needed. Just connect the camera to your computer and start receiving images just like a web camera!

The USB Video Class (UVC) standard 1.1 supported by the camera guarantees the use of the camera on all operating systems (Windows, Linux, Mac etc.)  The UV-1551LE-C camera is ideally suited for use as an industrial web camera in kiosks to video conference systems.

Configurations are available as a board level version with no lens mount (Model UI-1552LE) or with a S-mount lens adapter included (Model UI-1551LE).

Full Datasheets and manuals can be downloaded below for each version
Model
UI-1551LE
UI-1552LE

For all your imaging needs, you can visit www.1stvision or contact us! to discuss your application in further detail or receive a quote.

 

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This camera provides Versatility, Performance and a nice price. What is the JAI’s GO 5000 series?

JAI’s GO 5000 delivers an exceptional blend of high versatility, excellent performance, small size and best of all at a price of < $1K.  


The GO provides the perfect starting point for a wide range of machine vision applications.


The GO-5000 packs a high performance 5-megapixel CMOS imager (Anafocus Lince5M) into a compact form factor that fits in your fingertips. Using a combination of ROI and binning capabilities, this tiny camera can become almost anything you want – from a super-fast VGA camera (at nearly 450 fps) to a super sensitive camera using binning to create 10-micron, or even-20-micron effective pixel sizes.

High image quality
The GO-5000’s imager features a combination of analog and digital gain controls to reduce the amount of quantized noise in low-light images compared to conventional CMOS imagers offering digital gain functions alone. On the color models, an on-chip 4-channel analog gain function is utilized to allow individual adjustment of R, G, and B information for better white balancing with reduced noise.

Even at megapixel resolutions, the GO Series doesn’t resort to a rolling shutter or small pixels with low signal-to-noise ratios. 5-micron square pixels, global shutter, analog gain control, a built-in lookup table, and other advanced features help ensure image quality beyond entry-level expectations. 

Choose of image size and frame rate using Multiple ROI & binning options
Featuring multiple binning options and single or multiple ROI’s the GO-5000 can be easily configured to meet a wide range of customer requirements for resolution, speed, and optical formats.

For example, by creating a centered 1920 x 1080 ROI, users can configure the GO-5000 to provide high-speed 1080p HD video that fits completely within the optical format of a 2/3” C-mount lens. This is in contrast to CMOS cameras with 5.5 micron pixels which generate 1080p image sizes that are slightly larger than the standard 2/3” optical circle, thus requiring more expensive 1” image optics to ensure that vignetting will not occur.
Note: frame rates shown above are for GO-5000-USB and GO-5000-PGE, respectively.
Monochrome models feature a range of binning options including 2×2 and 4×4 binning to allow users to effectively create 10-micron, or even 20-micron, square pixels to maximize sensitivity and signal-to-noise characteristics for specific applications, as well as increasing the overall frame rates.

Choice of interfaces
Choose one of the advanced digital interfaces that best fits your needs. Options include powered interfaces (PoE) where a single-cable solution is desired, as well as both frame-grabber-based (PMCL) and “grabberless” configurations using GigE and USB3.0


Small size and weight
GO Series cameras measure 29 x 29 x 41.5 mm (excluding lens mount) and weigh less than 50 grams, enabling them to fit into small spaces or into vehicles or other applications where weight is critical.

The GO-5000 is one of the smallest 5-megapixel cameras available and weighs only 46 grams (lens not included)
 
Want additional information?  Full Datasheets for the GO 5000 can be found HERE.


For all your imaging needs, you can visit www.1stvision or contact us! to discuss your application in further detail.  
 
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