This is kind of continuing on from another post where I asked about the canon 50mm 1.4 versus the Sigma 50mm 1.4 and the opinions really were divided.
Rather than compare canon with other lenses and thrashing out the differences, I'm interested to find out which non-canon lenses (Sigma, Zeiss, Tamron etc) people own, what they are using them for and why they love them.
I own the following Nikkor primes -
20mm 3.5 AIS
28mm 2.8 AIS
35mm 2.8 AI
50mm 1.8 AIS
50mm 1.2 AIS
The 20mm I haven't really found a use for because it tends to vignette on a 5D. I love the 28mm 2.8 for landscape photography, it's very sharp and puts out beautiful images. The 35mm and 50mm are great for video.
The great thing about these old primes is they are cheap and very well built, metal housings, with aperture rings. Although I believe the achilles heel of these older lenses is moisture. The seals may not be up to the standards of todays Canon L series lens. It's not uncommon to see these lenses selling on Adorama specifying 'mold or fungal' damage.