Because 1995.
Reminds me of my teenage years. In one summer in Switzerland a Swiss friend and I disassembled several times the motors of his collection of small old motorcycles. Everytime when we reassembled them we found spare parts: screws, washers ... that we have missed. The funny result was that w/o these parts the motorcycle was running even a tad faster.Can't resist a naughty comment on a typo - I am pretty good at losing screws but not at finding them.
Good shot! I still do have the same lens, it was my first L and tele lens, too. It also works flawlessly until today, 1st gen IS is a bit noisy but not really loud. My wife has the comparable lens from Nikon, the AF-S Nikkor 300 f/4 D IF-ED, and despite the fact that it is technically more primitive (no VR = IS) it needed already two times a new AF drive. The 1990s AF drive vom Nikon btw is extremely slow compared with the EF 300mm f/4 L IS USM. Canon was technically miles ahead of Nikon back then.
We had that discussion elsewhere: I guess we'll never see a new 500mm f/4 prime in future from Canon, since the EF 600mm Mk III is already only 50 g heavier than the first EF 500mm prime, the f/4.5 L USM lens with 3 kg, introduced in 1992. Now the RF 200-500mm f/4 is announced, which surely is the next nail in the 500 f/4 prime coffin. Maybe they'll bring later a simpler RF 500mm f/5.6 on the marked, as patented recently. If they could offer such a smaller prime on a decent price level, I guess it could be a success and a good competition against Nikon's Z 600mm f/6.3.
