A method is disclosed for selecting a minimum of one wavelength 320 or a minimum of one wavelength range 206 of electromagnetic radiation to be used for object testing, whereby a first spectrum is captured or calculated on a first point of a first object 509, a second spectrum is captured or calculated on a second point of the first 509 or a second object, a difference spectrum is formed from the first and the second spectrum, and the minimum of one wavelength 320 or minimum of one wavelength range 26 is selected in the difference spectrum according to predetermined criteria; as well as a microscope 500 with means of the illumination 502, capture 503, and analysis 504, whereby the illumination means illuminate an object 509, and the capture means capture a first spectrum on a first point on a first object, the capture means capture a second spectrum on a second point of the first or on a second object, and the analysis means form a difference spectrum as a difference between the first and the second spectrum. The disclosed invention enables selection of an optimally suited wavelength for object testing.