Question

1. Explain the difference between resolution and magnification. Refer to the following scenario when preparing your response.
   If I have 500nm light exciting an object through a 100X NA=1 objective, what is the approximate resolution of the image?                                               (1 page limit)

Answer 1

Resolution and magnification are two important parameters in geometrical optics in which we are required to design some optical elements such as telescopes, microscopes etc.

Lets find the difference between these to parameters.

Magnification is the parameter which determines how many times the size of the object (not in physical science) can be increased using loptic elements. It is simply magnifying an object using the combination of lenses and mirrors. But resolution is the ability to distinguish to closely spaced objects using a particular wavelength of light. resolution is dependant on the numercal aperture and the wavelength of the light.

If we are observing a 10 micron size object through a microscope, if the size of which is measured as some 1000 microns, then the magnification of the microscope is 100. Its just zooming the object. But if two obects are closely spaced by say siome 10 microns, still if we are able to see them both as seperate, then we can say that the resolution of the instrument is good. In optical as well as in digital magnification, the resolution can be decreased with zooming, which is dependant also on the NA of the material.

Two see two closely spaced objects seperately, Rayleigh criterian has to be satisfied. Since we are observing the object through an apperture, the diffraction can happen and the diffraction of light from both objects should be in such way that, the central maximum of one should overlap with the first minimum of the other.

While considering given problem, It can be seen that 100X given here is the maximum magnification of the objective. That means the objects size can be seen as 100 times( maximum) as large as the original size of the object while lokking through the objective. The wavelength used is 500 nm which has an influence in the resolution of the objective. The numerical apperture is given by

,

Where n is refractive index of the objective and is the diffraction angle maximum for the apperture. here NA=1.0

and = 500 nm

Then the resoultion of the objective is given by the Rayleighs formula,

ie is the resolution of the given objective.