Abstract: A portable variable focus microscope includes a housing having a lower section and an upper section secured together. A lens is removably disposed on at least one lens retention feature of the upper section. The scope further includes a slide platform and a height adjuster, where rotation of the height adjuster within the scope housing adjusts a relative distance between the slide platform and the lens to adjust a focus of the lens. The scope may be used in conjunction with a mobile data device to capture an image of a sample on a slide received in the scope. A program including a CNN algorithm may be employed to identify contaminants in the sample.