Stabilized long lens for < $850!!!

Epinions doesn't allow embedded images, which is a shame for camera/lens reviews. Hence, I've posted some images taken with this lens here:

http://www.geocities.com/tom_jhou/tamron_200_500.html

I previously tried this lens on a Canon SLR, and found it surprisingly sharp, lightweight, and cheap. However, I could only hand-hold it for bright sunlit subjects. Hence, I preferred my stabilized, but costlier, heavier, and shorter Canon 100-400L IS lens.

Well, now that I have gotten the Minolta 5D, with in-camera stabilization, I tried this lens once again, hoping the 5D's anti-shake would improve handhold performance. Indeed, it does. Where I needed 1/800 second shutters to handhold the Canon version, I can get by with 1/200 sec for the Minolta version. For an $850 lens plus a $650 camera, this is a lot of bang for the buck. The lens and camera together cost less than what some places charge for Canon's 100-400!

The trade-offs
The main tradeoff is autofocus speed. It's not awful, but on my camera (the 5D) it is not usually fast enough for flying birds or airplanes. However, because the focus motor is in the camera body, newer camera bodies may focus faster. The Sony Alpha DSLR has been reported to focus faster than the 5D, although I don't own one, so I can't confirm that.

Even with the slower 5D, the autofocus is pretty quick if the lens is already focused near the subject of interest. But there is a big caveat. For example, if you're aiming at a bird in the sky, it's easy to accidentally point the lens at the empty sky near the bird. The lens will then lose focus, and will take 2 seconds to cycle through its entire range before it comes back. It may even cycle several times, by which time the flying bird is usually gone.

The Tamron is slightly dreamy wide open, and doesn't reach optimum sharpness until f/8. (The Canon 100-400 was like that too, though it performed somewhat better when wide open). To see how stopping down improves sharpness, take a look at the first image on this page:

http://www.geocities.com/tom_jhou/tamron_200_500.html

As you can see, f/8 is a BIG improvement over f/6.3. Another thing to note is that Minolta's in-camera sharpening is relatively weak, and all f-stops benefit greatly from additional sharpening in Photoshop (USM radius 0.5 pixels, 150%). This is also reported to have been improved with the Sony Alpha.

My pet peeve: no pictures in Epinions!
I've said this many many timse: I want Epinions camera/lens reviews to allow embedded photos, or at least thumbnails. After all, the pictures are the whole point of cameras and lenses! I've sent this request to Epinions, to no avail. Until Epinions brings their site into the 21st century, I'll have to host my images at my Yahoo/Geocities site, and you'll have to cut and paste the external links I've provided to see the images. Sorry.

Now back to my review:

Purple fringing
The Tamron has noticeable purple fringing around bright edges when used wide open. In fact, this is a common problem with Tamron lenses, as their 18-200 lens had it also. It's much worse than either the Canon 100-400 IS or the Sigma 50-500. Fortunately, purple fringing can be (mostly) removed with the following free Photoshop plugin:

http://www.sd3.info/pf828/CAfree/CAfree0-1.html

Focus accuracy
Focus at 500mm is a bit tricky. My copy of the Tamron has a slight but noticeable front-focus, relative to my Minolta lenses. I was astonished to see this problem at all, because Tamron has an unusually good working relationship with Minolta, and a number of Minolta lenses are in fact Tamron rebadges. Hence, I'd expected perfect compatibility.

If you are brave, the Minolta 5D and 7D have 3 hex screws on the bottom of the camera that adjust the position of the autofocus sensor. To counteract front-focus issues, simply turn the screws counterclockwise. This greatly improved the Tamron's autofocus, at the expense of making my Minolta lenses back-focus by the same amount. Because I currently use the Tamron more than the other lenses, I adjusted my camera to the Tamron, but obviously this is not a long-term solution.

No autofocus limiter
For distant objects, Tamron could have doubled the lens' focus speed, at low cost, by adding a focus limiter. But they didn't. Canon and Nikon put focus limiters on their better telephoto lenses, and I really wish Tamron would also, as this would greatly improve this lens' utility with wildlife photography.

Improvised push-pull action
Having used Canon's push-pull lenses, I like their ability to rapidly zoom in and out. It makes it easy to find a target at low zoom then quickly zoom in to shoot.

The Tamron is not marketed as a push-pull zoom, but it has that capability anyway. Simply grab the front of the lens, and apply force. The lens barrel will extend smoothly, turning the focus ring as it goes. The motion is smooth easy, and unforced.

Real-world example
The page I linked to above also has a handheld 100% crop of a cardinal taken under horrible conditions. It was cloudy and dark, and I had to use ISO 1600, but I was amazed this lens gave me anything at all - handheld! Here is the link again:

http://www.geocities.com/tcchou71/tamron_200_500.html

Of course, I had to apply NeatImage and some sharpening, but the net result isn't so bad.

Summary
If you're interested in telephoto lenses you will either pay a lot, or live with limitations (or both!). For a budget lens, this one is not bad, unless you are interested in flying birds, where the slow autofocus will really hurt. Optically it is decent, although it has more purple fringing and less contrast than the Sigma 50-500. So even though sharpness is similar, the 50-500 "Bigma" images look better straight out of the camera. However, the Sigma is extremely heavy, and I could not handhold it for significant periods, whereas I have no trouble with the much lighter Tamron. This is not a perfect lens by any means, and in fact can be frustrating to use at times. However, in the $1000 range, there isn't much to choose from, and this is one of the better options.