ES MPCC Fält Flattner ED APO + Nikon T2

Many refractors have a curved image field, rather than a flat one. This means that only the central region is fully focused - the edges are out of focus. The human eye can generally compensate for these image properties, but cameras show increasing lack of focus towards the edges of images. The field flattener resolves image field curvature, thus drastically increasing edge clarity.