New with this lens includes Rear Group Focusing System (to facilitate compactness), reduced weight and size, improve optical formula to reduce chromatic aberrations and a closer minimum focusing distance and small minumum aperture for greater flexibility of operation. Mounting has been considerability with the bayonet mount. ecause of the exceptional balance and light weight of this lens, it can be hand-held with great ease. It is an outstanding lens for any SLR system because of its combination of telephoto impact and easy portability. SPECIFICATIONS: * Type: Mirror telephoto * Construction: 7 elements in 6 groups * Angle of view: 12 degrees * Minimum Aperture: F/32 * Closest Focusing Distance: 5ft * Filter size: 52 * Lenshood: built-in * Length: 4 3/4 in * Weight: 15 oz.