[Zig]

...er..continued, sort of:
These are 100% crops of the captures at f8. Straight conversions from raw, no sharpening or pp of any description.
Make sure you read my astonishing conclusion later..

Tamron, centre:


Canon, centre:


Tamron, edge left:


Canon, edge left:


Tamron, lower:


Canon, lower:


Astonishing Conclusion: The Tamron and the Canon are both nice.

General: If you want to scrape pixels(and there really is no point), you might notice the Tamron has the tiniest edge on resolution and detail at f8..the Canon does great but don't misconstrue its acuity and microcontrast for resolution.
Yet again, also bear in mind the following: the Canon does darn well compared to many primes here, hits the ground running at f4 and does even better at 70mm than at 90mm, sharpening up again by 135mm before softening at around 185mm onwards. Distortion is noticeable at 70mm on the Canon but is well controlled thereafter. Corner and edge sharpness are the compromise with the 70-200mm f4L(IS), becoming an issue if you want to stay uncropped from f8 in the top right when using lengths from, say, 90mm to 170mm. It's the best tele-zoom of the Canon line-up and is a whole lot lighter(and cheaper) than the f2.8 version, which is just about equally stonking.
The Tamron: if you think it's done well across the frame here at f8, it's even more of a ripper at f5.6, where it is, from my(limited) experience, easily as outstanding as any(possibly excepting the 35mm) Canon L prime. Appreciably softer at full aperture(f2.8), yes, but even by f3.5 it kicks into sharpness, again at f4, still holding its own at f11 before diffraction-softening begins: no big deal though.
Both the Tamron 90mm and the Canon 70-200f4L(IS) are excellent, both giving you a multiplicity of uses: the portraiture and landscape use of the latter, especially with IS, make it a winner, with its immediate full-aperture performance giving a sense of confidence. The Tamron is both a jack of several trades and master of them too: I often forget its raison d'etre as sharp short-macro it is, though its softness at f22 and smaller needs an eye to be kept out: I find it a scintillating lens for landscapes and portraits.
Finally, I've based my "observations" on a full-frame DSLR: the Canon's edge performance is obviously augmented in use on an APS-C camera, though the Tamron is stonking on both. Zones 1 and 2 with the Canon on full-frame, are "up there".
There we are then: a lot of Zig waffle and short on objective substance, but hey, we're friends, right? :|

[Toad]

Hmm. That is a pretty awesome comparison. I have know for years that the Tamron 90mm was deadly sharp - but I would have assumed that the high end Canon would beat it at some focal length. Because I actually own the Tamron, I am delighted of course.

Food for thought.

[nia]

This was so nice dear Zig, I mean the comparison, you did great. They both seem very well, I am one of Canon users but I don't have so long experiences for to talk.

Thank you dear Zig,
with my love,
nia

[matthew]

Nice to see - and I can empathize with the difficulty and labour of having to find differences between two exceptional lenses. These two both have stellar reputations and test results, so good on you for trying.

[Irma]

I don't have any of those lenses, so I can't speak from my experience.

Thanks for your review Zig. They are always very detailed and interesting....

[Keith Alan]

I notice that your examples from the Tamron look warmer, or perhaps the Canon leans towards blue?

[Zig]

Yep, you just hit my shame button there ...as I said in my list of cockups, I, er, had a polariser on the Canon but not on the Tamron, not fully doing its business but there nonetheless; I took the Canon shot as the cloud cover just started to pull over the sun, thus cooling the shot and adding that tad of spurious polariser-saturation at the same time.
This has to be the worst objective test I've both done and seen, ohyes.

[Wedding Shooter]

Thanks Zig - perhaps a better comparison might be between the Canon 100 Macro and the Tamron 90 Macro?

The Tamron is very well regarded.

[Zig]

Come on Chris, that would make far too logical sense and would require me having to know what I was talking about

...besides, that is just what they'd expect us to do....:|

[Toad]

Come on Chris, that would make far too logical sense and would require me having to know what I was talking about

...besides, that is just what they'd expect us to do....:|

Hah!!

[Wedding Shooter]

You are a funny man Zig My 100 Macro is my sharpest lens.