A lot of people might think that the biggest lens they could ever get for their camera is the Sigma Super zoom - 200mm to 500mm f:2.8. That's the green zeppelin seen in the heading image.
We got to see one in the shop a few years ago and it was certainly impressive. I was scared of it in case it rolled out of the case and onto my foot - I would be equally frightened of tripping over it due to the expense. Someone, somewhere needs one of these and if that someone is you, be prepared to search with your wallet.
But you probably have a different scope to your needs - both physically and financially - and your upper limit lens may be quite a bit smaller. Many, many DSLR shooters have benefited from other Sigma lenses in the past, as well as the more expensive teles of the major body manufacturers. I even know an outdoor shooter who went through serial Sigmas, having dropped the original one off rocks at the seashore into the surf. Hooray for insurance.
Okay, that's big and long - you can reduce the big while still seeing the long if you resort to a mirror lens - the catadioptric photo lens has one aperture only but can be tiny compared to the full-length regular lens. Long-distance shooters whose images do not include bright highlights may get away beautifully with a cat. They even show up on the used market, and some of the Eastern European ones were built like artillery - possibly because they were made in the same factories...
But think again about your own size limits when you look at the shorter lenses. I see beautiful zooms and primes all the time that have fast apertures and apparent quick auto-focus...and then sadly turn the page when I look at the details. Some too heavy, some too expensive, and some too darn big in diameter.
I work on tabletops and depend for a realistic look on a lens that can mimic a small human figure. The giant zoom with the 82 mm filter size and huge front element is never going to get close enough to the horizontal surface to do this unless you sink the camera and lens below the horizontal and just use part of the view. I want the smallest diameter front element that I can get, and would even welcome a right-angle adapter to get the camera body up out of the shot as well. There is a reason architects used to use an inverted periscope to walk through their miniature constructions. Here's what an 18mm Fujinon does in the hangar at Stein's Air World:
Other professional circumstances might benefit from size going up or down. Smaller lenses are less confronting for portrait sitters or animals - but may be more impressive for corporate clients. Small on a long journey would seem to be jollier than large - but landscape artists take along giant tripod and even bigger filter system holders anyway so maybe they don't notice. Street shooters do notice, and hope no-one else does.
But don't let any of the foregoing stop you if you find a lens that looks as if it will be wonderful. The mirror-less camera body has opened the way for the use of a myriad of adapters. You can put extremely strange lenses on to mundane cameras and get some exciting results. It is probably true to say that the classic oddities that you adapt to your camera do not actually do any better than the regular lenses from the maker - and in some cases a lot worse - but there are all sorts of character in older lenses as well as a retro feel to the ergonomics that prove rewarding. You can become the demon of the second-hand sales.
