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Star tracking is an essential technique for imaging of deep space objects with lenses and telescopes that have comparatively long focal lengths. See the Canon 28mm f/1.8 image below for an example of sagittal astigmatism. Since large amounts of resources were channeled towards research and development, production figures itself were low. The important thing for you to do is to generally determine what maximum shutter speed will work best for your particular camera and lens combination. The downside of this is that it is relatively heavy, and large-ish. (especially for a 4/3 lens)Optically this lens is very good; it focuses very close too, which is useful with a fisheye.