Excellent Optics at Consumer Prices

I just bought my first SLR camera, a Digital SLR, back in November 2007. I expected to quickly outgrow the kit lens included with most cameras, and so a lot of time was spent researching and talking with friends to find the ideal lenses for me. I quickly learned the game of compromises between price, optical quality, specs and models.

I'm not an authority on optical quality, so I'll avoid commenting on things like barrel distortion and vignetting for the most part. What I can add is, in studying both consumer and professional reviews, this lens is a true performer. And I can give you some insight on the factors that surfaced in my decision.

Aperture and Depth of Field
For my purchase, the biggest contender was the Canon 17-85mm f/4-5.6 IS. Optically, the Tamron is said to surpass it easily. The IS (Image Stabilization) on the Canon provides a theoretical 3-stop advantage in hand hold-ability. This means you can shoot with a slower shutter speed, but that advantage is lost when shooting a moving target. With a larger f/2.8 at your disposal, the Tamron can shoot with a faster shutter speed, giving you a better chance at stopping action and getting a sharp shot.

An aperture of f/2.8 is something you don't commonly find on a consumer lens, particularly a zoom lens. Larger apertures also provide a shallower depth of field, or the effect of everything but the subject being blurred, with a nice bokeh (the quality of the blur). This can be a highly desired effect, such as with portraits.

The larger aperture also provides more light in the view finder, which is especially noticeable on something like the Canon Rebel XT that has a less than ideal view finder. Compared to a friends kit 18-55mm f/3.5-5.6, there is a night and day difference.

I must add that I do find myself fighting the shallow depth of field (DoF) on occasion. An example is chasing a couple toddlers around the house. f/2.8 is often necessary to get enough light for low light indoor shots without a flash, and generally gives enough for stopping action. However, if two kids are not next to each other, the DoF can result in one child being out of focus. It's simply a fact of shooting with large apertures. IS can possibly remedy this with a slower shutter speed, but at the risk of being too slow to stop action. Adding light, such as with a flash, is the other solution.

Focal Length
At 17mm, it is wide enough to capture a good size room. I used it at an indoor car show and had no trouble getting entire side profiles of vehicles in a situation where I could only stand on the other side of the isle. On the long end, 50mm won't bring the world to you, but it is enough to give you the flexibility to be creative with framing your shots that you expect from a zoom. And 50mm is a respectable length for portraits, particularly on a crop body (see below).

17-50mm seems like a short range, but that seems to be one common trade off to getting good optics. Only consumer lenses having magical ranges like 17-200mm. Not that you can't take great pictures with such a lens, but, the larger the range in focal length a zoom provides, the more compromises likely exist. These compromises, necessary to achieve such a range, increase things like barrel distortion, vignetting, etc... This is a case if "less is more," where optic quality is concerned. The Canon 50mm f/1.8, a prime (no zoom at all), is very much a low cost consumer lens, yet it has very good optics (and cheap to boot) due to it's simplicity.

"Full-Frame" vs "Crop Bodies"
Many professional digital SLR camera bodies use full frame sensors that are equivalent in size to a 35mm frame. A great deal of Digital SLR camera bodies, particularly those aimed at general consumers, use APS-C size sensors. These sensors don't "see the whole picture". The result is a picture smaller than what a standard lens shows, or a crop of the "35mm picture".

Crop Factor: How it could effect your purchase
This cropping also gives the illusion of magnifying the shot as if you zoomed in. Imagine looking at a picture, cutting a rectangle out of it, and then stretching it to the original size. Everything looks bigger.

A Canon Rebel XT DSLR crop body has a crop factor of 1.6x. This means that the 17-50mm of this Tamron becomes the 35mm (or full-frame) equivalent of 27.2-80mm. Suddenly, that 17mm becomes a not-so-wide 27.2mm, and I think you might see where this can effect your shopping. A 28-135mm is a popular 35mm or full-frame lens, but that 28mm becomes closer to 45mm on a 1.6x crop body. That changes the potential purposes of that lens enough that Canon has the 17-85mm EF-S, a crop body version that that happens to work out to be 27.2-136mm.

Tamron Di-II and Canon EF-S
The standard 35mm or full-frame Canon EOS mount is designated as EF. EF-S is a Short Back Focus version, an indication that the lens is designed for crop sensors and moves the rear element closer to the sensor. The Di-II is simply the Tamron designation for essentially the same thing, in the case of Canon, an EF-S compatible mount. In either case, purposely building lenses for crop sensors means the lens can be smaller, lighter and faster (larger aperture).

Aside from that, it is important to note that Canon EOS EF-S bodies are compatible with EF and EF-S lenses. But EF-S lenses are not compatible with Canon EOS EF full frame or 35mm bodies because of the Short Back Focus. The mounts are designed in a way to prevent an EF-S (or EF-S compatible) lens from being mounted on EF only bodies. More importantly, if you ever intend to upgrade to a full-frame camera body, your crop body lenses will have to go out with the old, so plan accordingly.

Fixed Front Element
The front element does not rotate as they do on many entry level and consumer grade lenses. This is what allows for the use, and inclusion, of a pedal style hood. It also opens up options for special filters, such as gradient filters and polarizers, that require a specific orientation.

Center Pinch Lens Cap
A small thing, but Tamron includes a center pinch style lens cap that allows removing and attaching the cap with the hood attached. This seems logical enough, but it isn't something commonly included by other brands.

Potential Deal Breakers
There are a few things that make this less than ideal for a professional, or things that may be bothersome for some people.

No Full-Time Manual
One of the features of many Canon lenses with USM (Ultra-Sonic Motor), besides being fast and quiet, is that you get full-time manual. This feature allows you to leave the lens in auto-focus mode, but make manual adjustments at any time. Try that on any lens that does not have that feature, and you'll find yourself fighting the camera and possibly damaging the lens. I rarely manual focus, and, if I need to, it simply requires flipping the switch to manual mode.

Noisy Auto-Focus
Since this lens uses a standard focus motor, it is noisy. But don't let that trick you into thinking this lens is slow. While I haven't done comparisons myself, I've found info elsewhere that shows that, although this lens uses a standard motor, this lens is very comparable to Canon USM lenses in terms of speed. The noise itself was never an issue for me.

Rings Turn Opposite of Canon
If you find yourself using Canon lenses, or other lenses with focus and zoom rings that turn the same direction as Canon, this could be a nuisance. I have switched and borrowed lenses with friends, and didn't see it as an issue for me, but I also don't have years of habit and second nature to throw me off.

Doesn't Fit Full-Frame Bodies
As mentioned before, this lens is made for crop body (e.g. EF-S mount) cameras and it will not fit higher end full-frame (e.g. EF only mount) cameras. I bought this lens in lieu of the kit lens, so this lens will likely stay with my Canon Rebel XT, even if I upgrade.

Quality
I haven't handled all that many lenses, let alone used them for extended periods. That said, the Tamron 17-50mm f/2.8 feels vastly more solid than the Canon 50mm f/1.8 and the kit lens (Canon 18-55mm). The zoom and focus rings turn nicely, the lens mounts snugly on the camera body, and there is no sign of zoom creep when holding the camera facing downwards. If you get overzealous with the rings, there is a firm stop with no unexpected deflection (springy feeling) and no odd clunking or cracking sounds.

In 8 months, I have fired a few thousand shots through this lens with no changes. No looseness or sloppiness has developed.

Tamron also includes a 6 year warranty vs. Canon's standard of 1 year.

Final thoughts
This is an excellent alternative to a kit lens. For those willing to sacrifice features like IS and USM, this gives the consumer a budget option with specifications that promise to perform and without compromises to optical quality.

In other places, I have seen the optics compared to the Canon 17-55mm f/2.8 IS USM, a $1000 lens. My wallet is not that well endowed, so I cannot validate those claims. However, in my experience with this lens, I've seen nothing to refute those claims either and if the Tamron comes even remotely close, it's a bargain at about $450. I have been extremely pleased with performance and results. In a vast majority of situations, I can get away without using a flash.

There are comparison tests out there, with comparison shots, so you can judge for yourself. I was convinced that this is optically superior to the Canon 17-85mm f/4-5.6. I also decided that f/2.8 was more advantageous for my needs than IS, a trade off I have never regretted. Your options may weigh out differently, but the Tamron 17-50mm f/2.8 is a true winner for me and I highly recommend it to anyone that simply cannot afford or justify the cost of coveted Canon lenses.