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Below is my take on optical calculator that helps with adapting a microscope objective to your camera for macro-photography. I originally wrote it as a quick helper tool for assembling my current optical inspection setup. It worked pretty well, so I decided to share it here. And before anyone asks – yes! It works not only for phono styluses but for bugs and bees too!

Optical System Calculator


Light

Sensor

Objective

Outputs

Theoretical introduction

Practical application


Input Field Explanations

Light

  • Wavelength: Slider to adjust wavelength of light illuminating object.
  • Wavelength (μm): Wavelength converted into micrometers.
  • Color: The perceived color corresponding to the selected wavelength.

Sensor

  • Type: Monochrome is set by default. This means only light intensity is sampled and sensor resolution is the same for all wavelengths. Color – assumes worst case Bayer filter influence on color sensor resolution when using monochromatic light.
  • Format: Select the type or size standard of the camera sensor to update sensor width and height.
  • Resolution: Select standard sensor resolutions to update sensor width in pixels.
  • Sensor width (mm): The physical width of the sensor in millimeters.
  • Sensor height (mm): The physical height of the sensor in millimeters.
  • Sensor width (pixels): The horizontal resolution of the sensor in pixels.
  • Pixels per Rayleigh distance: Number of pixels covering the diffraction-limited spot size (Rayleigh criterion).
  • Pixels per Circle of Confusion: Number of pixels spanning the diameter of the Circle of Confusion, relating to perceived sharpness.

Objective

  • Type: Finite is assumed by default.
  • Magnification: The optical enlargement provided by the objective lens.
  • Aperture (NA): Numerical Aperture; defines the light-gathering and resolving power of the lens.
  • Field Number: Diameter of the observable field in the intermediate image plane, in millimeters.
  • FOV object side (mm): Field of view on the sobject side, in millimeters.
  • Nominal Tube length (mm): Standard distance between the objective and eyepiece for focus and nominal magnification.
  • Used Tube length (mm): The actual distance used in the setup. For infinity-corrected objective this is tube lens focal length.

Output Field Explanations

Sensor

  • Sensor diagonal (mm): The diagonal size of the sensor in millimeters.
  • Pixel size (μm): The size of each pixel on the sensor, in micrometers.

Optics and Resolution

  • FOV image side (mm): Field of view diameter in the intermediate image plane.
  • Tube magnification: Magnification introduced by the mismatch of nominal and used tubes.
  • Crop magnification: Effect of the sensor size compared to a full-frame reference.
  • Real magnification: Combined magnification considering objective and sensor.

Aperture and Resolution

  • Effective aperture: The effective aperture at sensor, adjusted for the tube magnification and Numerical Aperture.
  • Optical resolution (μm): Smallest resolvable feature on the sensor, based on the wavelength and numerical aperture.
  • Sensor resolution (μm): Smallest resolvable feature based on pixel size and number of pixels per Rayleigh sampling distance.

Focus and Depth

  • Circle of Confusion (μm): Maximum blur diameter still perceived as sharp.
  • DOField (classical) (μm): Depth of field using geometrical optics.
  • DOField (wave) (μm): Depth of field considering wave optics and diffraction.
  • DOFocus (mm): Depth of focus at image plane where the image remains sufficiently sharp, when moving only sensor.
  • ΔTube Tolerance: Tolerance to variation of Tube Length, where we can refocus image and not loose any sharpness. Doesn’t apply to infinity-corrected objective.