Is This Custom Lens Design Suitable for My Needs?

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Discussion Overview

The discussion revolves around the suitability of a custom lens design for a specific CMOS sensor application, focusing on parameters such as focal length, aperture, and imaging distance. Participants explore the technical aspects of lens design, including aberrations and depth of field, while considering the user's non-expert background.

Discussion Character

  • Technical explanation
  • Exploratory
  • Conceptual clarification

Main Points Raised

  • Arie presents a custom lens design with specifications for a CMOS sensor and requests feedback on its suitability for focusing on objects between 50m and 200m.
  • M Quack suggests that while commercial alternatives exist, the complexities of lens design, such as correcting chromatic and spherical aberrations, are not addressed in Arie's initial query.
  • Arie reiterates the question, seeking confirmation on whether the specified lens parameters will meet the focus requirements.
  • M Quack calculates the f-number and discusses the diffraction limit in relation to pixel size, indicating that the proposed lens parameters should theoretically allow for adequate imaging resolution.
  • M Quack notes that real lenses may not achieve the theoretical limits due to aberrations and emphasizes the importance of checking the lens's illumination over the image field.
  • Arie expresses gratitude for M Quack's detailed response, acknowledging a lack of full understanding but recognizing the information as helpful for further learning.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the overall suitability of the lens design, as M Quack provides technical insights while Arie seeks confirmation without fully grasping the complexities involved. The discussion reflects a mix of technical validation and the user's need for further understanding.

Contextual Notes

Limitations include Arie's non-expert status, which may affect the interpretation of technical details, and the discussion does not resolve the practical implications of real-world lens performance versus theoretical calculations.

ariebl
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Hello
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
Arie
 
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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:

http://www.bhphotovideo.com/c/product/404253-REG/Fujinon_HF35HA1B_2_3_C_Mount_35mm.html

http://www.bhphotovideo.com/c/product/519677-REG/Pentax_C33500KP_C33500KP_2_3_C_Mount.html

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

http://en.wikipedia.org/wiki/Numerical_aperture

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.

http://en.wikipedia.org/wiki/Rayleigh_criterion#Explanation

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.

http://en.wikipedia.org/wiki/Depth_of_field

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.
 


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 really appreciate your help
Arie
 

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