Using simple lenses to image AFM Probes

  • #1
Aymangh994
15
2
Hello,
Using a CCD camera and simple lenses, the probe of the cantilever and its surroundings are to be imaged. Since the cantilever is 50 um wide and some of the surroundings are to be imaged, the optimal image magnification is from 4 to 8. I therefore used a convex lens with a focal length of 88...98 mm. The object distance is 110 mm and extends over a deflection mirror.

According to the lensmarker equation, the distance to the image is 440 ... 880 mm. My question is, it is better to use a telephoto lens in this context or is a simple lens enough? The telephoto lens should then be constructed by yourself. As far as I know, this consists of a front lens and a rear lens. The front lens should be a convex lens and the rear lens should be a concave lens.

How big should be these two focal lengths in order to get a total focal length of 97mm using these two lenses. How large should be the distance between the two lenses and the distance between the rear lens and the CCD sensor?
I have another problem choosing the type of the lens (ashperical, spherical or achromatic lens) ?

Thank you and sorry for my bad english
 

Answers and Replies

  • #2
Aymangh994
15
2
Hello,
since I know that a telephoto lens consists of a front convex lens and rear concave lens, I want to construct a telephot objective by myself. The focal length of this objectiv should be between 88 to 98 mm. Is there a formula to calculate the distance between the two lensen and the distance between the rear lens and the Camera sensor ?
Thank you in advanced
 
  • #3
Andy Resnick
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Hello,
since I know that a telephoto lens consists of a front convex lens and rear concave lens, I want to construct a telephot objective by myself. The focal length of this objectiv should be between 88 to 98 mm. Is there a formula to calculate the distance between the two lensen and the distance between the rear lens and the Camera sensor ?
Thank you in advanced
There's no such formula, but if you know the magnification and separation distances, you can determine the two lens powers. Kingslake's book "Lens design fundamentals" has a few worked examples in sections 3.4.6-3.4.8 and 14.2
 
  • #4
Aymangh994
15
2
Hello everyone,
I want to choose a lens, but i am confused about the lens type. I know that chromatic and spheric lenses cause Aberration. So my Choice will be either aspheric or achromatic lens. Since acromatic lens consists of two lenses, it is no thin lens anymore. Or am I wrong about that ? An AFM Probe should be imaged, so the image will be in micro range.
The Light is 450 nm, Please help me how to choose the right one ? Here is a Screenshot of a few achromatic lenses. According to which criteria should the choice be ?

Best regards
 

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  • #5
hutchphd
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There may be some language issues (so apologies if I misunderstand).
Lenses intrinsically have deviations from ideal behaviour. One cannot eliminate all these aberrations but can minmize a chosen subset. That choice is determined by the design criteria for the optical system. You have given (to me at least) no exact idea what you are trying to do.
 
  • #6
Aymangh994
15
2
Thank you very much for your support and Help. I appreciate it
I would like to image a measuring probe using a CCD camera. A simple lens is used instead of an objective. Spherical and chromatic lenses have an aberration. The cantilever is 50 µm wide and should be imaged sharply with its surroundings. The light used is 450 nm and is emitted diffusely. The light radiation is reflected by two white umbrellas. I need help choosing the focal length and lens shape or aperture? There are many choices of suppliers based on the coating and the light used. Does the coating play a role in this context?

My Idea :
Since the cantilever is 50 µm wide, the optimal lateral image magnification is 4 to 8. Accordingly, according to the lens maker equation with an object distance of 110 nm (large for deflection via deflection mirrors) the focal length will be 88 to 97.8 mm. To avoid spherical or chromatic aberrations, I would like to use either an aspheric or achromatic lens. The light is emitted diffusely from the side of the camera and is evenly reflected by 2 white umbrellas.
 
  • #7
hutchphd
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Object distance 110 nm?
If you have essentially monochromatic light why worry about chromatic aberration?
If you need an image why not use a "regular" camera lens? Is the camera homebuilt? If you need a large depth of field you need a lower f-number lens (and therefore sufficient illumination.) Silicon is not very sensitive to violet
 
  • #11
hutchphd
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Looks to me like number 4 in the Edmund line up might be best with that illuminant. You may need to "stop down" the lens to get the desired depth of field. Are there speed (frame rate/exposure time) requirements? When doubt build it up on the bench: Edmund is a fast (but not cheap) supplier of good stuff. Good luck.
 
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