The Nikon 105mm f/2.5 is perhaps **the** niftiest, most-compact, best-focusing 100 to 135mm lens ever made...it has an almost perfect manual focusing action...just a super design...it adapts pretty well to a Canon d-slr...the pre-Ai era models from the late 1960's are the lowest cost, while the variants made in the mid-1970's to the late 1990's cost more, but are a bit more 'modern' in their design. The later Ai-S version had the lightest touch focusing helicoid, and a built-in,sliding lens shade, and the Ai-S variant is an absolute dream of a lens, even when used as a manual focusing lens.
The 100mm f/2.8 Series E Nikon (not a Nikkor, but a 'Nikon') lens is lower-cost, plastic, and pretty cheap by comparison...it would probably be the lowest-cost 100mm f/12.8 lens from a name brand that could be found. The so-called "pre-Ai" 105mm f/2.5 lens models are not of a lot of use on modern Nikon cameras, but they WILL fit on Canons with adapters, and will mount and work, and those can be had for around $100 or so with careful shopping.
