Koehler Illumination

Koehler illumination is a method used in microscopes to provide even, bright lighting of the sample. It works by positioning an external light source so that its light passes through a condenser lens system, which focuses the light onto the sample. The key is that the light is adjusted so that both the light source and the image of the filament are out of focus simultaneously, resulting in uniform illumination without glare or uneven brightness. This technique enhances image quality and contrast, making observations more accurate and consistent across different samples.