I spent a long time thinking about a parallel comparison between the Canon 24-70mm f2.8 L Series Lens and Tamron 28-75mm f2.8 SP Lens. At time of writing there was a difference of over £650 between the two lenses, and it's not going to take a scientist to tell us that one of these lenses is going to come out on top; one's a Rolls or a Ferrari, but the question is what does that make the other? Maybe the answer isn't going to come from a direct comparison.
If you had one lens my guess is that one of these would be it. The speed and focal range are going to cover you for the majority of situations, from portraits to landscapes, sport to fashion, and whatever you can find in between. I've always been a fan of fast prime lenses, and never given too much thought to short zooms. Both the Canon 24-70mm f2.8 L Series Lens and Tamron 28-75mm f2.8 SP Lens have gone a long way to changing the way I think. If there's a zoom that's capable of doing the job of three primes, then why not? Shots can all too easily get missed whilst changing lenses, bodies, and in the old days film. It's about the ability to change your focal length in an instant. That's not to mention the sterling job that they do as macro lenses. The Tamron 28-75mm close focusing to 33cm over the entire range of the lens, and the Canon 24-70mm is not far behind on 38cm. I'd like to call that advantage Tamron.
F2.8 throughout the entire zoom range is a major selling point for me, giving you a fast wide angle and a fast short telephoto lens. There isn't a situation that I can think of where that isn't a great asset, and in the Tamron's price range it is an asset and a half .The scientists will tell you that this will also boost the quality of the mid range apertures compared to lenses that open up to say f4 at the wide end and f5.6 at the other (have a look at your compact for confirmation!) It's adding a wonderful extra stop in low light situations, and if that means handheld shots can gain a little extra in the shutter speed department, then that can be the difference between getting the shot sharp and hitting delete. Handheld, steady at a 30th is a possibility, steady at a 15th is lucky. I'm not keen on leaving it down to luck, so an extra stop is priceless, especially when you have no control of your light source.
The Canon is heavy, twice the weight pretty much of the Tamron, so we're already thinking that the Canon L series is a nice solid lens – as you would expect – and yes it is that, but in the Tamron's favour is that sometimes a little less weight is no bad thing, not just when it's in your bag, but also when shooting hand-held, and we're back to taking advantage of the shutter speed / aperture combo again due to the fast apertures. The Tamron conversely is light and more discreet in size, so if you're at all self conscious taking pictures in public, you're more likely to blend in with the Tamron.
Both lenses are pretty adept at (auto) focusing - the Canon has the edge here in terms of focusing speed, and is also quieter, but if your wallet is feeling the Tamron, being let down won't be an issue. If focusing speed is on your critical list of requirements, you've probably saved the dollars for the Canon. Something in common between the two? They both hunt around a little in low light looking for something with enough contrast to bite on, but find me a lens that doesn't.
The lens hoods differ quite widely too, the hood for the Canon 24-70mm f2.8 L Series Lens is at least double the size of the hood on the Tamron 28-75mm f2.8 SP Lens and made me feel like a paparazzi looking for a stepladder initially, but it is that size and shape for a reason. The bigger front element, compared to the Tamron, needs a bigger hood to protect from flare and fingers (especially when shooting at the wider end of the lens). Remove it at your peril, they don't come supplied as standard if you don't need them – unless of course you like a little artistic flare (as opposed to the type that makes you feel like you were squinting!)
The Tamron's hood is more compact but just as effective. There is a little niggle here in that the rear cap of the Tamron kept falling off in the bag. The solution? I stuck a spare Canon cap on the Tamron, job done. You can get them at Wex Photographic very cheaply and front and back spares in the bag are never a bad idea full stop.
Sharpness is the be all and end all right? Probably. It's an area that is crucial, but at the same time it's very easy to tirelessly get self absorbed with the technicalities, (leave that to the fellas that make the things - that's their domain, we just want to take the best pictures) I will always work on the "are the results any good" theory. I honestly can't remember a time when I've made a big print and I've got a magnifier out to look at the edge of the picture, giving it the full rubber glove examination. Let's not forget that if your focus isn't spot on then the sharpness issue has just gone for a Burton anyway.
Repeatedly we get told a good picture can be taken on anything, and there's a huge element of truth there, but I don't want to take my pictures on just anything, I want to know it's a) a class act, b) won't let me down, c) will justify its use, and is of course d) sharp.
So to the actual sharpness of these lenses, the centres of both were excellent, a match for most 35mm lenses in their categories for sure. I'm going to go as far as saying that at the centres of the images, there's not a lot between the two.
The Canon 24-70mm however performs better at the extremes of the focal range, but in the 35-55mm range there's not much in it. All the shots I took with these lenses were taken with a Canon EOS 5D Mark II, which I guess is more than capable of showing the highlights and flaws of each lens. All the files I shot were RAW and one of the nice surprises was that the RAW files had a nice contrast to them and only required minor tweaking, and that was from the Tamron 28-75mm too; I've grown to expect that from the Canon, being a regular L Series user. Overall, as you move towards the edges of the Canon images, it "holds it together" more, as one would expect: you're not paying all that extra money just for a bigger lens hood! At the same time the Tamron holds its own pretty admirably.
I believe I'm right in saying that if your not using a full frame sensor camera body, then the edge of the lens isn't so important, which makes the edge sharpness of the Tamron less critical. Full frame cameras will tend to highlight the aberrations of any lens, no matter what the cost. If you are using a smaller sensor camera then the increased magnification will extend the long end of the lens into a really handy portrait lens.
I think the major factor here is cost. If you have the cash for the Canon 24-70mm f2.8 L Series I think your mind is made up already. The Canon is fully aimed at the pro market with its weather sealing and solid build. If you don't have the money (like most of us) and you're looking for a good quality fast zoom that stands up on its own, then the Tamron 28-75mm f2.8 SP will do you proud. I think you're getting a lot of lens for your money. The downside to the Tamron? The rear cap made me want to scream. However I'd love to see how the Tamron fares against other lenses in its class, my bet would be that it'd be pretty hard to beat. So, taking all of this into consideration, the Canon gets an "I want one" 9/10 and the Tamron not far behind on a healthy 7/10.
I shot these to explore the centre sharpness of the lens and get a feel for the macro side of things. Both lenses held up pretty good for me. The fall off here is due to the wide apertures being used (the images are also my preferred choices).
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