Leica Elmar 135mm F4 This lens is a fine performer.  Often overlooked for the later Tele-Elmar and APO-Telyt lenses of the same focal lengths, this lens can usually be found at bargain prices.  This lens is a good choice for those wishing to add this focal length to their Leica kit with minimal cost.  I like this lens and at the current prices, you simply can't beat it.  I have shot this lens and can tell you first hand that this lens is Beatifully sharp from corner to corner.  The lens is relatively small and  light weight in this focal range and makes a great travel lens.   135mm F4 Elmar 1960-1965 Type 1  SN#1,717,000-2,156,000 Finish Chrome Mount Rigid Lens Elements 4 in 4 Groups Filter Size 39mm Apertures F4-F22 Angle of View 18 Degrees Minimum Focus Distance 1.5 Meters Units Produced 23,395 Weight 440 Grams With a filter size of 39mm, this can be the part of a great travel kit along with your 35mm Summicron.  A convenient tripod socket was also attached to this lens, and it also has a removeable optical group for use with the Visoflex system.