You've only taken a couple hundred shots with the camera and lenses so far? If that's accurate, you might want to give it a little more time and get some more experience with the gear before making any decisions.
The lens you have used most is the 50mm? If so, then that might be the one that would be the most useful to upgrade.
However, if you haven't been using this gear together very long, it really might take a little longer to learn to "get the best out of it".
OTOH, if the 80-400 is really that frustrating and you aren't getting any good results out of it, it might be a problem lens and maybe is the first lens you should replace. Is it an older lens that you bought used or something? Lenses do wear out or have de-centered elements or other problems inside, even though they look fine outside. However, less than 50-60 shots so far with the telephoto zoom (and I bet some of those were with the longer end of the 18-135)? That's hardly enough to learn how to use it well. Long telephotos require some work to get a good shot... especially when they don't have stabilization.
If it's really not doing the job, that 80-400mm probably is the lens you most need to consider replacing. Besides the Canon 100-400mm, you also might want to look at the considerably less expensive Sigma 120-400 OS and 150-500 OS.
If I were you, I'd keep the 18-135 for now... or at least make it your lowest priority for replacement. I'm assuming it's the same age as your camera, came with it as the kit lens."
No one should say 24-105 is "no good" or that it "isn't wide enough on crop".... It is what it is. It's a useful, quality "standard to moderate" telephoto lens. A nice, versatile "walk-around" lens that meets a lot of peoples' needs pretty well. What matters is what you complement it with, what other lenses you have in your system. Personally I will never spend what the 24-105 costs for a different reason... I can buy 28-135 IS for 1/4 or 1/5 the price and get virtually the same results. But since you have the 18-135 already, there's little to be gained. That appears to be a reasonably good walk-around lens. I'd only fault it because it doesn't have USM focus.
If you have a lens that's "not wide enough" need wide, get a wide lens (Canon 10-22, Tokina 12-24, etc.). Yes, some people go a different route, put together a different set of lenses such as a 11-16, 17-50, 70-200. But someone using a 100-400 or similar might find a combo of 10-22, 24-105, 100-400 more convenient and useful. Neither choice is "right" or "wrong" on any camera format.
You do apppear to be shooting "as wide as possible" quite a bit (second only to 50mm and 135mm, the latter is probably "as long as possible" when you have the 18-135 on the camera). So, you might want to consider adding one of the wider lenses sometime, if you truly feel that you just can't get wide enough with what you've got.
dropmyload wrote in post #14161743
I've taken 4000+ shots, only 297 were worth putting on Flickr. I don't upload everything, just what is worth sharing.
You can see a few shots at 200mm plus because really nothing worth sharing, all lousy shots. I bought the Tokina used on Ebay...noisy autofocus, sometimes doesn't even lock... that's why I use it in manual.
I was thinking the same, get the 100-400L and deal with wide end next year.
EDIT: Okay, that makes sense. I didn't think of Flickr statistics... There are free software applets you can run on your computer that give you shot statistics for all the images on your hard drive(s), not just the ones that turn out good enough to want to post online. I sort of assumed that was what you had done. Still, 4000 isn't a great deal either (that's roughly three weeks shooting for me, on average). But it certainly might be enough for you to decide what you like and what you don't....
You need confidence in your longest lens, so that's still probably the best place to start. I see you are in Kenya and I have no idea of lens prices and availability there... But still would suggest looking at the two Sigmas as well, if at all possible. The Canon 100-400 is a "push-pull" zoom... uses a single ring for both focus and zooming. Some people like that. Others don't (I'm one of the ones who don't). Some say it makes the lens more of a "dust vacuum" than some other zooms, perhaps because the zooming can be done so quickly. But I have no personal experience with the lens so can't say if this is true. It is an older lens design now... It's IS needs to be manually turned off when it's locked down on a tripod (the IS on some newer lenses auto senses lack of movement and turns itself off). OTOH, it seems an ideal lens for some fast moving events, such as air shows or birds in flight.
The two Sigma are considerably less expensive (around 35% less here in the U.S.), seem to be well made and are newer designs, released in the past two or three years I believe. Some feel the newer Sigma OS is better than the older Canon IS. Optically they seem close... The Canon might have a little edge but I see a lot of good shots being done with the Sigmas too (you might want to search for sample images from each of these lenses here). Both of the Siggies are the more traditional two ring design. The 120-400 OS is fairly compact, close to the same size as the Canon lens. The 150-500mm is bigger and heavier... might want a monopod more often with it.
EDIT (again :rolleyes... If you are using the longer lens mostly for wildlife, sports, action... You might want to consider trying Back Button Focus technique with your camera. This is an old Canon sports shooter trick, works well with any moving subject, but really can be used with most anything. Then it's important to switch to AI Servo and often advisable to use only the center AF point. Doing that I can nail focus on moving targets 95 out of 100 times (with various crop cameras... not so much with 5DII). I call it my KISS or "Keep It Simple, Stupid" mode.