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Verify custom lens design

by ariebl
Tags: custom, design, lens, verify
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Apr3-12, 03:26 AM
P: 3
Need to verify please if the following custom design lens is reasonable
-- Sensor: CMOS sensor, 1/3, 6μm x 6μm pixel, Wide VGA 752H x 480V, 4.55mm x 2.97mm Imaging Area
-- Focus: 50m till 200m
-- Lens: f2.8; Focal length=34mm; Diameter=13mm
Pay attention I am not a physicist and also that this data is only for first estimation and not for lens production
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M Quack
Apr3-12, 04:48 AM
P: 672
Those number say very little about the lens, except that you should be able to find several commercial suppliers that can supply something similar for a reasonable price. Just a few examples I found after ~7 milliseconds of googling:

What is difficult in lens design is to correct chromatic and spherical aberrations, distortion, anti-reflective coatings etc. You mention nothing of that.

Why do you want to design your own lens?
Apr5-12, 02:28 PM
P: 3
thank M Quack for your answer
but let me, please, write my question in another words:
I have CMOS sensor, 1/3, 6μm x 6μm pixel, Wide VGA 752H x 480V, 4.55mm x 2.97mm Imaging Area
And I need to add a lens to receive a focus from 50m till 200m
Can you please tell me if lens with f2.8, Focal length=34mm and Diameter=13mm will be OK?

M Quack
Apr6-12, 07:56 AM
P: 672
Verify custom lens design

Focal length 34mm divided by diameter 13mm gives f/2.6, so that part is OK.

Next, you want to check if the diffraction limit is better than your pixel size. Most lenses, however, do not reach the diffraction limit at f/2.8 due to unavoidable aberrations.

You get about 2 micrometers, so that is OK, too, and with some margin to allow for less-than-perfect performance of the lens.

Finally, you want to check the depth of field to see if objects between 50 and 200m can be in focus. Use the pixel size as circle of confusion.

The hyperfocal distance is about H=70m. If you focus your lens to that distance, then objects from H/2=35m to infinity will be in focus, i.e. the circle of confusion will be smaller than the pixel size.

So your parameters 34mm f/2.8 should allow you to image objects between 50 and 200m with better than 6 micrometers resolution onto your detector.

These estimates are valid for a perfect lens. Real life lenses will perform worse for the resolution limit. The size of the CCD does not enter anywhere here, but real life lenses will illuminate only a limited image field. So you need to check that when selecting the lens.
Apr6-12, 08:49 AM
P: 3
Thank you M Quack very very much
I just finished to read your answer and it looks great
not that I understood everything, but it is exactly what I was looking for
because I'm not a physicist I need to learn more a bout it
but I understood lens seems OK but need to test a real lens
again I realy appreciate your help

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