Camera recommendation

[Arrouma]

Hello everybody,
I have an urgent question, please if you could help me to choose the  camera for my project:

I would like to detect the 
If you can help me choose the camera required for my project
I want to detect the presence of different cms components of length 2mm and width 1.2mm in an electronic card length 23cm and width 13cm.
I tried with a webcam Logitech HD pro c920 it gave me a clear picture well detailed by bringing closer the webcam but it necessitates a 3 captures to cover the whole image since the focal length of this camera is important.
I want to do this inspection with a single snapshot using a better camera usb3 BASLER presented in the national instrument site below, that will not exceed $ 700. is it possible? And what are the camera characteristics that I have to take into account ?
http://www.ni.com/en-lb/shop/select/area-scan-camera
Thanks in advance

[Kemens]

Hello Arrouma,

From what you have described, I believe the key things you will have to look into is your camera resolution (calculation in link above) and max frame rate (lower will generally get you a camera that cost less at a given resolution).  The resolution calculation will depend on the smallest feature you need to detect and not your smallest component.  So, it is going to be smaller than 1.2mm.  You can also filter on the shopping page based on your interface (USB3) to see what the prices look like for a given resolution.

The next important part of your system is your camera lens, which will depend on your focal length, working distance, field of view (23cm), and sensor size.  The formula and example calculations are also included in the above linked KB.

[Arrouma]

Unfortunately sir, the link does not work, if you could resend it,
Thank you

[Kemens · Accepted solution]

My apologies, there was as space at the end of the url, give this a try:  https://www.ni.com/en/support/documentation/supplemental/18/calculating-camera-sensor-resolution-and...

[SimonAldred]

There are two things you need to focus on (excuse the pun).

i) What lens do I need to image the board onto the sensor so that the image just covers the sensor

ii) What resolution camera do I need to see the components with sufficient detail.

The problem is that i) and ii) are not necessarily independent  as higher resolution cameras will generally be larger. So inevitably a degree of iteration is required to come to a satisfactory solution. 

I would choose a camera that you think is a good candidate. Take the sensor width and divide it by the width of your board -  this will give you the magnification required to image onto the sensor. The magnification M is equal to the focal length of your lens (f) divided by the distance of the lens from the board (L). M  = f/L.  So you can calculate f  if you know L. If L is large you will need a longer focal length lens. Conversely if L is small you will need a shorter focal length lens (wider angle lens). Now the question is - can you get a lens of the required focal length?  Assuming that you can then the next question is - is the sensor resolution sufficient to resolve the detail you want to see. If it is then great -  you have a solution. If not then you need to go round the loop again with a higher resolution camera bearing in mind that the sensor size will be different leading to a different magnification requirement. I usually create a spreadsheet in excel to do all the calculations automatically. 

[Arrouma]

According to my calculations I chose a lens with focal distance 4mm so that I place my camera close to the board and cover all of the field of view. But I was not recommended to use it since they said me that it can cause very great distortion. Is it true? Do i have to use focal length greater than 9mm.
Best regards,

[SimonAldred · Accepted solution]

This is correct.  A 4mm lens is a wide angle lens that will most likely give you some image distortion. Standard C mount lenses usually come in focal lengths of 6mm, 12mm, 16mm, 25mm. If possible I would increase the camera to object distance and use a longer focal length lens. Typically I would use 12mm, 16mm and above. The disadvantages of moving the camera further away  include less light reaching the camera and possibly greater impact of vibrations, but usually this is not such a problem - only in extreme circumstances. As long as the ratio f/L meets your magnification requirement you should be fine.