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CMOS Sensor lens parameters

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plasmatic

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I am designing an Iris capture system with a cmos sensor module. There are different lens mount available like with specifications like

f3.6mm, F2.0 BW
f4.9mm, F2.8

I do not have much info about optics. What do the terms fx.y , FX.Y & BW indicate? Can you please provide some links where this would be described in easy to understand terms.

Which of the two are more suitable for close capture of iris? Or do I need to add another lens to capture iris from a distance of 10 ~ 15 cm from the device?

Thanks
 

Sensor size is going to play a part in what lens you want to chose,

the f3.6mm etc is the focal length of the lens and basically determines the field of view of the lens, say 90 degrees or so for a 3.6mm lens on a 1/3" chip.

F2.0 etc is the F Stop of the lens and is how much light it lets in i think, it will determine the minimum illumination that is needed to get a clear picture. BW i would think is Black/White.

Lens choice is very important as much or even more so than sensor choice.

A good quality lens will make all the difference.
 

You find some basic imaging equations together with this nice lens catalog
 
I have 2 choice of lens for the same image sensor size : 1/4"

f3.6mm, F2.0
f4.9mm, F2.8

Since the lower focal length would give more lower image size (more FoV) would it better to go with f4.9mm lens for my application of eye capture?

Another consideration is image sharpness. What lens parameter determines this? Do I need a custom lens for this?
BTW, the camera module is C3038 using OV6630 sensor. Any idea if this is suitable for my application?

Thanks
 

what resolution is the chip you are using??

Normally i would go with the tighest field of view that i can as this will achieve the best pixel density (clarity)
 

ok so that is only about 0.1MP so not a very high resolution, I have no idea what resolution you require but i think the focal length of the lens would be a big part of how well this works,

How do people look at the lens??

I would decide the exact FOV (field of view) that you need and then get a lens with a focal length to suit this. You will find lots of calculators online and they will also tell you the pixel density you will get so you can see if this is good enough also for what you require,

How are you reading the sensor after that??
 

ste2006 said:
ok so that is only about 0.1MP so not a very high resolution, I have no idea what resolution you require but i think the focal length of the lens would be a big part of how well this works,

How do people look at the lens??

The subject will look directly into the lens.


I would decide the exact FOV (field of view) that you need and then get a lens with a focal length to suit this. You will find lots of calculators online and they will also tell you the pixel density you will get so you can see if this is good enough also for what you require,

How are you reading the sensor after that??
Click to expand...

I think CIF resolution is enough for algorithms and pixel density should be around 96ppi. See attached figure to get an idea.
After capture the gray scale image is read entirely into the buffer for processing.

With this info would it be possible to say if I can achieve the required performance from the sensor? I can always try it but just want some theoretical figures to get an idea about the quality that can be achieved.

Thanks!
 

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To capture from 10-15cm, at a guess I think you'll need a larger focal length than 4.9mm. Maybe more like 12mm even 25mm (guessing). You can google for "focal length calculator" which will help.
The last few pages of the doc that FvM recommended will also help you. Machine vision cameras are the types of cameras you probably want; the black-and-white
ones are quite sensitive, and the lenses often have an aperture adjustment on them too (smaller aperture will mean you won't have to be so careful to get the eye in the exact plane, but will require greater illumination, so it is a compromise).
 

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