Resolution refers to the ability of a microscope to distinguish two separate points. Magnifying an object without good resolution will simply produce a large image of the object where details cannot be identified.
Magnification, focus and resolution are terms often used when describing microscope images. Each term describes a specific attribute of the image produced by a microscope.
Magnification describes how much larger an image is compared to the actual object. A magnification of 100x means the image is one hundred times larger than the actual object.
The objective lenses on a microscope have a very narrow focal point. An image outside this focal point will appear blurry. Microscopes are equipped with focus knobs that move the specimen up and down to place the image in the focal point of the lenses.
Resolution refers to the smallest distance between two objects at which the objects still appear distinct. If two points are close enough together, they will appear indistinguishable from each other. If the two objects are within the resolving power of the microscope, they will appear separate. It is resolution that allows the details of a specimen to be observed.
Limits of Resolution
Resolution depends on the numerical aperture (ability to gather light) of the objective lens and condenser and the wavelength of light. Adjusting any of these will alter the resolution of the microscope. Due to the wavelength of light, the ideal limit of resolution in a light microscope is about 0.25 micrometers. Specimen quality, illumination and alignment of the microscope generally reduce the practical limit of resolution.