Tamron 18-270mm vs Canon 18-200mm vs Canon 18-135mm vs Canon 18-55mm+Canon 55-250mm --Which should I get?

270 needs more light. As does the 250.

IE Slower shutter speed and/or larger aperture.

So you’re buying a great camera (I’m a Nikon man myself, but I looked it up and the 50D seems pretty good)
The first thing you want to look at is the aperture (or f-number) – Imagine the lens like the pupil of your eye, when there is lots of light, it shrinks and when there is not much is has to open wide. The larger the aperture the more light it can let in. Read This
All of these zoom lenses have a changing aperture (i.e. f3.5-f5.6) This means that as you zoom more, the lens lets in less light and the shutter has to open longer.

The Tamron is 3.5 – 6.3 meaning that at the lower zoom range (18mm = f3.5, where as at 270mm = f6.3) this however is not a bad thing, at 200mm you are most likely to be at 5.6, meaning you get the same aperture range as the the canon 18–200 f3.5–5.6 which, at 200mm, is also 5.6.
i.e you get the same apertures between the two up until 200mm, therefore at this point the extra 70mm from the Tamron is basically a bonus.

Next is the focusing speed, however this is basically not worth mentioning. LEARN HOW TO MANUAL FOCUS. get good at manual focusing and you will be able to focus quicker than any lens in this price range. I used a 70–300mm manual focus with my first body (a Nikon D40) for about a year and over that time got pretty good at manually focusing.
With action shots, unless you have a super fast lens (i.e a constant zoom of 300mm at 2.8) it simply wont autofocus fast enough.

My opinion is go with the Tamron, you get a quality lens at the same price (or cheaper?) than the canon with a wider zoom range, which will serve you well in your travels.

To give you an Idea im travelling with my kit pretty soon using a Nikon D300, a Sigma 24–70mm f2.8 Across the entire range :D, Nikon 50mm f1.8 and Sigma 70–300mm f4–5.6 Macro.

I Would highly reccomend getting the little 50mm f1.8 (Tamron, Sigma, Canon, they all do one) an aperture of 1.8 in low light is amazing and allows you to take low light indoor shots with out a pesky (and ugly) flash.

TL;DR – get the Tamron

Look at the extra weight issue carefully. The all-in-one lenses are heavier and may be more or less the same as the 18–55 plus the 55–250. Also, the 18–55, now with IS isn’t a bad lens for just toodling around and it is REALLY light.

Tamron has a good reputation and their lens is bigger. Realeyes really likes Tamron lenses, but he doesn’t use the all-in-one. The drawback, as you have seen in the reviews, is the lens creep (which was the dealbreaker for me—although if you remember to put the lens lock on it’d be okay), and the softness at the extremes.

It’s all a ballance of price, hassle, and quality. The all-in-one lenses are great for convenience and travel, but you sacrifice quality. The 2 kit lenses are great for price, but you have the hassle factor of switching lenses, and they’re not as fast as the Tamron (although with the IS it’s actually pretty good as you gain a couple of stops).

I went through the same decision making process and I ended up deciding to keep my 18–55 and my 55–250 lenses, and I’m happy with them. Frankly, though, for travel I now have a Canon D90 powershot which is REALLY convenient and takes decent pictures. I use my DSLR now mostly for astrophotography.

Having read over your question properly, I still think you should stick with the Tamron (which was my original recommendation).

While all-in-one lenses do compromise quality to some extent, I think the drop in quality will be negligible, assuming you’re a hobby photographer and don’t plan to make very large prints. I shoot with the Nikon 18–200 VR very often and I can’t tell you how convenient it is sometimes to have such a versatile lens on hand.

I have, however, read that the quality of the 18–200 is quite bad – corner softness and chromatic aberration in particular.

The Tamron is supposed to have slightly slower autofocus, but if you’re not shooting sports, and if you will be shooting in decent light most of the time, I don’t think that will be an issue.

Thank you all for the great feedback. All good points.

I did look into the weight difference between the two Canon lenses and the Tamron – 20.9 vs 19.5 oz makes the Tamron lighter by just 1.4 oz. I’m not fanatic enough about ultralight hiking to base my decision on an ounce.

Cost wise, I think the two Canons would run $250—$300 combined while the Canon 18–135mm is $320 new on EBay and the Tamron is $450 new from authorized dealer right now with $150 mail-in rebate and $30 retailer discount.

I am leaning towards the Tamron just because I don’t want to have to even think about changing lenses right now. Then there are the kayaking type situations where it isn’t possible to change the lens without risking water damage. I’d love to save a hundred bucks but I think the one lens will work best for now.

When I bought my daughter a camera on eBay from a commercial photographer, he cautioned me not to buy used lenses on eBay because there can be mold inside the lens. A new lens is the way to go. When I purchased a Tamron lens at the local camera shop, they confirmed the advice about the possibility of mold inside used lenses. It can cause the lens to stick.

@BarnacleBill, you’re right about the mould issue, but this only really happens in older lenses that have been around for a bit, if the equipment has been looked after properly then there shouldn’t be too much hassle. Most listers will say “No mould” or something to that effect, however if they don’t say. Send them a question and take a screenshot of the response etc in order to cover your arse if worst comes to worst. I have bought 2 lenses off eBay and both times I’ve payed half of what the stores wanted brand new and they have been in perfect nick.

Well, if you want only one lens, then I agree with @xxii, get the Tamron. My only concern about it, besides the obvious risk of water damage from kayaking, is the slow autofocus if you’re, say, going to take a picture of a bird in flight. But whatever—it’s a faster lens, so you can decrease the shutter speed. Like I said, I almost bought that lens myself. I’d really like to hear what Realeyes says since he’s a professional and gave me a lot of good advice when I was agonizing over the same topic.

I’d like to hear what he has to say too. See the autofocus was a concern for me because I really get a kick out of taking photos of stuff moving like that, especially when it’s really far away. Now I’ve also heard that the contrast is not as good as the Canons. Can some people really focus as fast as autofocus on some of the lenses? I mean when I go out on whale watching tours and I stand next to the dudes with their 5D and massive telephoto lenses, I’ve never seen anyone manual focus in that situation. It’s an interesting challenge because you never really know where the whales are.

@lilikoi Pro’s with there 5D’s or D3’s or whatever have proper telephoto lenses, nothing like what has been discussed in this thread. They are generally a fixed focal length at an aperture of 2.8. this means that all the bulk goes into the autofocus as opposed to moving the glass elements meaning the focus is much faster. Using a cheap(er) lens such as these all rounders the bulk is kept down by skimping on the AF motor (or just using the cameras) meaning the AF is much slower. Therefore I find that that manually focusing is just easier, although I may have just got used to it seeing as I was using a lens with no AF at all for over a year

@lilikoi Well, if you have a fast lens, a fast autofocus may not be as much of an issue if you’re shooting something like whales far away.

For travel and action shots the range of the Tamron sounds like a winner. But as @joeysefika recommends : learn how to manual focus.
I’d probably pick the Canon 18–200 to get quality image all through the range. That’s really a pretty wide range too, and there are times I’d want a fast autofocus.