Tamron SP AF17-50mm F/2.8 XR Di-II LD ASPHERICAL [IF]

by Bob Atkins, 2006

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Part I | Part 2 | Part 3

The initial impression of the Tamron SP AF17-50mm F/2.8 XR Di-II LD Aspherical [IF] is that it's a solid lens. It feels "dense". Not heavy, but it gives the impression of solidity. The body seems to be made of a composite (plastic) material and the finish is in low-reflectivity black with a gold ring. Both the zoom and manual focus rings are covered in rubber with ribbing to make them easier to grip. The MF/AF switch is located near the lens mount and there is a "lock" button which can be used to lock the zoom at the 17mm position.

The Tamron SP AF17-50mm F/2.8 XR Di-II LD Aspherical [IF] uses High Refractive Index glass (XR) to lower aberrations and make the lens more compact, Low Dispersion glass (LD) to minimize chromatic aberration and two Hybrid Aspherical Elements to further reduce residual aberrations and reduce the physical length of the lens.

The zoom action is positive and smooth and the lens shows no sign of "zoom creep" (zoom setting does not change when the lens is pointed straight up or straight down). Canon users will notice that the zoom is "backwards" compared to Canon lenses, i.e. focal length increases when the zoom ring is turned to the right (clockwise from the rear). On Canon lenses focal length decreases when the zoom ring is turned to the right. The zoom can be locked at 17mm (presumably so that the lens can be locked at it's minimum length for carrying), though as I said, there isn't really any zoom creep under normal conditions anyway.

Focus is also "backwards" for Canon users, close focus is obtained with the focus ring turned all the way to the left (anti-clockwise looking from the rear), whereas with Canon lenses close focus is obtained with the focus ring turned all the way to the right.

The length of the lens increases by about 1.1" (28mm) at the 50mm setting compared to the 17mm setting. Focusing is internal, so the lens does not change length when focused. The front element does not rotate during focusing or zooming, but the manual focus ring does rotate during autofocus. I could feel no side-to-side or up-and-down play in the barrel when extended. The zoom is marked at focal lengths of 17mm, 24mm, 35mm and 50mm. The zoom range covers the same field of view as a 27-80mm zoom would on a full frame camera, so applications of this lens range from landscapes and interiors, to travel and portraits.

Close focus is 27cm (10.6") at all focal lengths giving a magnification of 0.22x at the 50mm setting.

A bayonet fitting "petal" style hood is supplied with the lens. The Tamron SP AF17-50mm F/2.8 XR Di-II LD Aspherical [IF] also comes with the standard Tamron 6 year warranty

LEFT: Tamron 17-55/2.8 ; RIGHT Canon EF-S 17-85 IS

Autofocus

The Tamron SP AF17-50mm F/2.8 XR Di-II LD Aspherical [IF] uses a conventional focus motor, so focus isn't silent like it is with Canon's lenses using USM motors. However the noise level is still pretty low and I can't imagine it being a problem for 99.9% of users (DSLRs make noise due to mirror and shutter movement anyway, so you can't shoot in absolute silence).

When mounted on an EOS 20D DSLR, the time taken to shift from 0.27m to infinity (or infinity to 0.27m) averaged 0.40 seconds. The time to cycle from infinity to 0.27m and back to infinity (i.e. the widest focus search range) was 1.44s, the lens pausing for 0.644 at the close focus setting before returning to infinity. In comparison, the EF 17-85IS USM takes about 0.315s to go from infinity to 0.35m and the full cycle (infinity - 0.35m - infinity) takes 1 second.

Here's an audio clip of the lens cycling from infinity to close focus and back to infinity. Audio Clip ( 169K .wav file).

Performance

I chose to compare the Tamron SP AF17-50mm F/2.8 XR Di-II LD Aspherical [IF] with the Canon EF-S 17-85/4-5.6 IS USM for two reasons. First, they are around the same price and so may be considered by users as alternatives. Second, because I had an EF-S 17-85/4-5.6 IS USM available! Obviously, based on zoom range and aperture, comparison with the EF-S 17-55/2.8 IS USM would also be valid and interesting, but (a) Canon didn't lend me one for review and (b) the Canon lens is $750 more expensive ($1200 vs. $450), which will exclude it for many users.

Distortion

As you can see, there's some barrel distortion at 17mm, but not as much as the EF-S 17-85 IS shows. You pretty much have to expect some barrel distortion at the short end of wideangle zooms. It's quite easy to digitally correct in PhotoShop (or your favorite alternative image editor). Distortion is much lower at 35 and 50mm as you can see from the images below, in fact distortion is pretty low over the whole 20-50mm part of the zoom range.

Vignetting

The following images were shot using and EOS 20D camera. They are "as shot" except they have been resized:

There's mild vignetting wide open at 17mm but it's much reduced by stopping down. Unless you are shooting a uniform target (as I was), it's not likely that the effect would be very noticeable in normal images. It's possible you might see darker corners if shooting landscapes at f2.8 with a uniform sky (though I'm not sure why you'd shoot a landscape at f2.8!).

Slight vignetting is detectable with the lens wide open at 50mm, but it's pretty much completely gone at f4. Again the amount of vignetting seen wide open at 50mm would be very unlikely to be noticeable in real world images. Vignetting at intermediate focal lengths (e.g. 35mm) was actually lower than at 17 or 50mm and should not be a problem, even wide open.

Next: Part 2