Lens Test Results

The Contestants: Canon 24-70 f/2.8 L, Tamron AF 28-75mm f2.8 XR Di, Canon 24mm f/2.8, Canon 50 f/1.8

Procedure: I put these lenses on my Canon 20D on a Manfrotto tripod and recorded the images in Canon raw format. I converted them to TIFs in Photoshop and cropped each image down to the center region of the image at 100% magnification (i.e., "actual size" in terms of pixels). I converted them all to B&W/grayscale to take color differences out of the comparison. No sharpening was done.

My main interest was the amount of detail resolved. I care less about contrast or sharpness because those can easily be modified in an image editor, like Photoshop. In all of the images below, the lens was autofocussed on the floodlight (which angles from upper left to lower right) near the center of each image.

24mm @ f/5.6 (Tamron at 28mm)

Canon 24mm @ f/5.6

Tamron 28-75 @ 28mm & f/5.6

Canon 24-70 @ 24mm & f/5.6

This is a somewhat difficult comparison to make because the Tamron is 28mm versus 24mm for the other two lenses. Surprisingly, to me, the 24-70 looks like it's resolving more detail than the 24mm prime. The Tamron 28-75 and the Canon 24-70 appear pretty close to me (try to ignore the differences in contrast and look for details), but it's difficult to say because the Tamron lens has a bit of an advantage due to its smaller FOV at 28mm vs. 24mm.


50mm @ f/2.8

Tamron 28-75 @ 50mm & f/2.8

Canon 24-70 @ 50mm & f/2.8

I started to see more detail in the results from the 24-70. Notice the clearly evident crease at the edge of the floodlight bulb on the right; this is much less evident on the left in the Tamron.


50mm @ f/5.6

Tamron 28-75 @ 50mm & f/5.6

Canon 24-70 @ 50mm & f/5.6

Canon 50mm f/1.8 @ f/5.6


Note: I had taken a shot with the 50mm at f/2.8 for the previous comparison, but the focus was clearly off; so I didn't use it.

To my eye, the 50mm and 24-70 resolved more detail than the 28-75. I think the 50mm prime and the 24-70 were very close to one another, and depending on what you visually study, you might declare one or the other the "winner"; I'd say it pretty close to a dead heat between them.


70mm @ f/2.8

Tamron 28-75 @ 70mm & f/2.8

Canon 24-70 @ 70mm & f/2.8

At 70mm, you start to see that the downward-pointing, cup-shaped floodlight holder has some raised lettering going vertically along the shadow/highlight border. I didn't realize this raised lettering was there until I saw the 24-70 image at this focal length. There's not a huge difference in detail between the two at this focal length and aperture, but the 24-70 is clearly resolving a bit more detail.


70mm @ f/5.6

Tamron 28-75 @ 70mm & f/5.6

Canon 24-70 @ 70mm & f/5.6

This may be worth a second testing, but the detail resolving power of the 24-70 (as one would expect) clearly increased when the aperture was stopped down from 2.8 to 5.6 while the detail resolving power of the 28-75 decreased when stopped down from to 5.6.


Overall, I'd say the Tamron 28-75 did a pretty admirable job. I actually owned a Canon 24-70 previously, but sold it and bought the Tamron* because: a) I thought the Tamron did a pretty darn good job, and b) I didn't want to own a $1200 lens until I was actually making money with my photography.

Well, zoom ahead one year: I'm making money with my photography and I want the very best lens I can get; also I want the extra 4mm of coverage, especially for indoor shots and because of the 1.6 crop factor on the Canon 20D. One other thing: for event photography, any increase in autofocussing speed you can get is going to pay dividends....i.e., I need the darn thing to focus NOW, not one 1/100th of a second from now, or I'm going to miss some shots.

In any case, I wanted to make sure I was going forward with a purchase of a 24-70 f/2.8 L; and I have proven--at least to myself--that the 24-70 will take me forward in terms of focussing speed, angle of view covered, and yes, image quality. Sure it's like 3 times the cost of the Tamron, but the absolute difference in cost ($800) and the way these Canon L lenses hold their value isn't really that big of a financial risk afterall..;-).

-Michael Grace-Martin


*Note: it took me two tries before I got a good copy of the Tamron 28-75.