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Specifically:

Sigma 18-50mm f/2.8 EX DC Macro (not the previous non-macro version. HSM is only on Nikon fit)

Vs.

Tamron 17-50mm f2.8 SP XR Di II LD VC Lens (not the cheaper one without vibration control)

Currently the Sigma is slightly cheaper and offers a macro ability but this question is only concerned with sharpness.

I'm not sure if it matters, but I'm only really interested in the Canon fit versions.

Thanks, Matt

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1  
I think the right question is: I'm considering the Sigma and the Tamron. Which, or both, is sufficiently sharp? Also keep in mind that usually/often the limiting factor in sharpness is technique, not the lens. –  Reid Jul 16 '10 at 13:45

5 Answers 5

I have the Sigma 18-50 f2.8 (non-HSM, non-MACRO) Made in Japan and the Tamron 17-50 f2.8 (non-VC) Made in China, both copies are for Pentax K-mount.

I would have to warn you about Tamron. The QC is very inconsistent and it really depends on whether you're lucky and get a sharp copy, or like me, who has a back-focusing copy with inconsistent edge distortion. I've sent out the lens to Japan for calibration, hoping it will arrive back sharp and well calibrated.

It is hard to talk about Tamron as there are currently 3 kinds of this lens: Made in Japan Assembled in China Made in China

If you're comparing a properly calibrated Tamron (which I had several years ago), performing the way it should to Sigma it will: -Tamron will focus slower then Sigma -Tamaron will be superior in producing less CA -Tamaron will be sharper wide open -I noticed that Sigma produces a very very slight warm tint which is pleasant in portrait photography.

However, unless you're able to get hands on a Made in Japan or Assembled in China (with Japanese parts) lens that will be properly calibrated, go for the Sigma.

That is strictly my point of view and coming from my previous experience over the last 4 years.

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I've not used the Sigma, but I own the Tamron 17-50 VC. It really is quite sharp, just as sharp as the than the 50mm 1.8 prime, comparing both at f2.8, in my experience

Also, when you're using slower shutter speeds, the VC does help prevent motion blur from camera shake.

As always, it's a lot sharper at f4 than f2.8, but all lenses are.

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A bit confused by a comma above; do you mean it's sharper when using slow shutter speeds? If so, that's a different problem than sharpness. –  ex-ms Aug 18 '10 at 20:53
    
These shots feel rather ad-hoc and subjective...I wouldn't take them as a definitive example of how sharp either lens is. There are more scientific ways of testing the sharpness of an image with official charts and lens mounting apparatuses. I recommend looking for an official review of both lenses. –  jrista Aug 19 '10 at 16:36
    
absolutely agree @jrista - however, since I couldn't find any straight comparisons, I did my own. Also, ignoring the pixel peeping, looking at the 8000 photos i've taken in the past 12 months, I'm generally happier with the clarity of the photos taken with the Tamron than the 50mm 1.8 –  Daniel O Aug 20 '10 at 15:41
    
what shutter speed was the 50mm f/1.8 shot taken at? And was it taken on a tripod? It looks like it has a little motion blur which would make it very hard to compare sharpness... –  drfrogsplat Aug 23 '10 at 5:25
    
Either the 50 f/1.8 shot is misfocussed, or the result of motion blur, or there's something severly wrong with your copy as I've seen it perform better than that wide open, let alone at f/2.8! –  Matt Grum Feb 27 '13 at 9:21

Comparing two very similar lenses like the Sigma 18-50mm f/2.8 EX DC Macro and the Tamron 17-50mm f2.8 SP XR Di II LD VC Lens in terms of sharpness can be difficult.

  • Often one lens will perform better at a particular focal length and aperture, while the other will perform better at other focal length and aperture combinations.

  • Even at the same focal length and aperture, one may be sharper at the center but not as sharp at the edges as the other lens.

  • When two lenses this close are considered, copy-to-copy variation for either lens may be more significant than representative examples of both models compared to each other.

As other answers have stated, there doesn't seem to be many places that have reviewed both of these exact models, so even comparative test charts like this one at The-Digital-Picture that uses the earlier non-Macro version of the Sigma aren't definitive. The non-Macro Sigma, by the way seems to be sharper overall than the Tamron, but not by much when the different magnification sizes of the charts are taken into account. (The non-VC Tamron, on the other hand, is clearly sharper than either.)

I did find a straight up comparison at DxO Mark. When I first selected each lens, the default camera body was the 7D for both. I was then able to select each lens as tested on a Canon 50D.

At the widest aperture of f/2.8 both lenses are very similar at the widest focal lengths. From 35mm to 50mm the Tamron is slightly sharper in the center but not quite as sharp on the edges. Center sharpness is very close for both at f/5.6 across the focal length range. At the edges at f/5.6 the Tamron is barely sharper at the widest focal lengths but is progressively sharper on the edges from 35mm to 50mm. At f/11 it is pretty much a dead heat from 17/18mm to 50mm. The Tamron measures an almost undetectable amount sharper at 24mm and 35mm.

Overall, the Tamron tested a little sharper than the Sigma on the 50D. In the real world I think copy to copy variation could well be greater than the differences measured by DxO Labs. When both were tested on the 7D, the Tamron clearly did better at f/5.6, but the Sigma compared better at wider focal lengths and apertures than when tested on the 50D. The Tamron also tested slightly better in terms of CA and Vignetting, but also had slightly more pincushion distortion at 17mm than the Sigma at 18mm.

The significant differences between the two lenses

  • Image stabilization. The Tamron has it, the Sigma does not.
  • Macro capability. The Sigma is laberled Macro, but that should be taken with a grain of salt. MFD is 7.9", MM is 1:3 (.33). The Tamron has an MFD of 11.4", MM is 1:4.8 (.21). So while not really a true Macro with 1:1 or even 1:2 magnification, the Sigma does much better than the Tamron in this regard.
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Here are some reviews, with data for the Tamron, but not the Sigma: http://www.popphoto.com/Reviews/Lenses/Lens-Test-Sigma-18-50mm-f-2.8-EX-DC-Macro http://www.popphoto.com/tamron/2010/03/lens-test-tamron-sp-17-50mm-f28-xr-di-ii-vc-af

And here with data for the Sigma, but not the Tamron: http://lens-reviews.com/Lenses/Sigma/Sigma-18-50mm-f2.8-EX-DC-Macro.html http://lens-reviews.com/Lenses/Tamron/Tamron-SP-AF17-50mm-F2.8-XR-Di-II-LD-Aspherical-IF.html

...other than those and other reviews you can find with Google, you might want to check Flickr for full size photos you can inspect in their original sizes to compare the lenses. Just make sure you get a large sampling of data since some people are better with sharpening than others and lack of focus, low light, and motion can all make a lens look worse than it is.

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I have not used either, but this website has quite a bit of data, you might try your comparisons there: Tamron sigma

I saw a new lens comparison website a month ago and it looked promising, but for the life of me, I can't find it now. I hope someone can post a link to it.

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Thanks for the links to the site (looks like a good site) however your sigma link refers to a different lens. It seems they don't have a review for the 18-50mm (macro version) –  matt burns Jul 16 '10 at 12:50
2  
The version of the Sigma lens he's talking about (the Macro version) doesn't seem to be on photozone.de. –  Erica Marshall Jul 16 '10 at 13:02

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