The idea of these types of lenses is that you screw them on to the front of your normal camera lens in order to change the closest focusing distance; in this case he focus is altered from infinity to 250mm from front of lens. In essence they allow you to get close up to your subject matter and are ideal for macro-photography. The 205D is designed to be used with most Canon EF lenses on the market and can also be used with PowerShot G1 and G2 lenses. The Canon 250D is a doublet type close-up lens that gives a correction for chromatic aberration. What this means is that the lens has two elements and is therefore said to give a performance that is much better than the less expensive singlet type lenses that only have one element. It is usually recommended that you should stop down to f/16 if you're using a cheaper one-element close-up lenses rather than a two-element lens.

In my experience the quality of this supplementary lens does seem to be outstanding and a perfect accessory to bring you closer to your subject when shooting macro photography, allowing focusing at a distance of 250mm.