Lenses For example, if the primary lens is 200 mm, and the reversed lens is 50 mm, then the magnification will be approximately 4× with both lenses set to their infinity setting. Keep the aperture wide open on the "front" lens, and control exposure with the aperture of the prime lens. This combination is rather heavy and cumbersome, probably lending itself more to the studio rather than field work. Depth of Field Achieving sufficient depth of field while maintaining high image quality is one of the greatest problems for a close-up photographer. In general, in close-up and macro photography, depth of field is extremely small, fractions of a millimeter in some cases, and becomes increasingly smaller with increasing magnification . There will be many subjects where it is not possible to obtain sufficient depth of field to render the whole subject sharp. It is always worth asking yourself whether you actually need such a high magnification, or whether a smaller magnification, with its correspondingly greater depth of field, is a better compromise. Always make sure to focus on the most important part of a subject (the eye of an insect, for example), and, if possible, align the main plane of the subject with the plane of the image sensor. This will ensure maximum possible depth of field, though may well lead to images that lack creativity. Consideration of depth of field and its effect on both image content and quality can become highly technical, with complex formulas for calculating it based on esoteric factors such as the size of the acceptable circle of confusion. In the end, what really matters, of course, is the appearance of the final image, and you will need to do practical tests to see how your equipment performs for the sort of work you are doing. Depth of field is dependent on the size of the sensor in the camera. A full- frame, 35 mm­size sensor will, for a given magnification, have a smaller depth of field than a smaller sensor. A sensor with a 1.5× crop factor will give depth of field values approximately 1.5× greater than the corresponding 35 mm­size sensor. Definition Depth of field can be defined as the distance between the furthest and nearest points of a subject that are acceptably sharp. When you focus 61