Sunday, November 23, 2008

Tamron Teleconverter Review

Since switching from my Sigma 70-300mm lens to my Canon 70-200mm, I've been happy with the results I get, but I do miss some of the extra range in that last 100mm. Even with the 70-300mm, there were times when I couldn't get close enough to the subject. I've been thinking about getting a teleconverter for a long time. After hearing good things about the Tamron Pro (SP) line of teleconverters, I decided to get both a 1.4X and a 2.0X and see how they worked out.

Choosing a brand/model
In chosing which teleconverter(s) to buy, I did quite a bit of research. The options were to stick with the Canon brand or to go with several of the other 3rd party brands. The Canon brand teleconverters were known performers, yet they weren't without their downsides. As expected, the Canon brand is more expensive. They were slightly heavier than some of the other options. Finally, because of the design of the Canon teleconverters, they aren't compatible will all lenses (not even many of the canon lenses). They mostly just work with more expensive Canon L series zooms (with a few exceptions).

On the other hand, looking at the other brands involved some tradeoffs. Yes they are cheaper and a little lighter, but image quality, build quality, and compatability are all issues to be concerned about. After doing a lot of research, I've seen a lot of positive information about some of the teleconverters from Tamron. They make a few series of teleconverters, and it is the more expensive ones (the Pro or SP series) which are the good ones. From what I read, they are a nearly an identical match for the Canons in terms of quality. I even found a review from one guy who bought both and found his Tamron teleconverter was sharper than the Canon. I looked at some test samples and was very pleased.

In looking around, I found the best prices on Amazon. The price for the 2X is pretty much the same everywhere...$210, however Amazon gives you free shipping. At that price, that makes it about $80 cheaper than the Canon 2X teleconverter (actually only $55 at the moment, since Canon currently has a $25 rebate). The price on the 1.4X, is about the same ($210) almost everywhere. However, it is much better on Amazon...currently about $140 with free shipping. That puts it at about half the price on the Canon 1.4X teleconverter.

Initial impressions

The Tamron teleconverters were very nicely designed. They had the same light gray coloring as the canon L series lense. They were small and light. Each teleconverter came with a nice black vinyl storage bag with draw strings. Even better, each bag was just big enough to hold both teleconverters, so you can carry them together and they'll take up slightly less space.

Tamron 1.4X and 2.0X Teleconverters

Model Numbers and UPC Codes

Basic functionality and performance

Giving them a quick try on the camera, they function just the way you would expect. The camera detects the teleconverter and reports the adjusted values for aperture (an f/4 lens becomes f/5.6 with the 1.4X and f/8 with the 2.0X). The EXIF data also properly reports the presence of the teleconverter by adding a +1.4x or +2.0x to the end of the Lens field.

When it comes to autofocus, you also get what you would expect. The lens focuses slightly slower to get a more precise focus in light of the higher magnification. Most cameras will only autofocus with an aperture of up to f/5.6. Thus an f/4 lens will autofocus with the 1.4X teleconverter, but not with the 2.0X. In order for the 2.0X to work, you'd need an f/2.8 or faster lens.

There is a way to trick the camera into autofocusing even without such a fast lens. You can place a small piece of clear tape over the 3 end contact pins of the teleconverter , which will break the contacts and prevent the camera from detecting the presence of the teleconverter. This means the teleconverter won't be reported in the EXIF data, and the f-stop reported won't reflect the teleconverter either. The plus side of this is that the camera won't refuse to autofocus. This seemed like a good idea in theory, but in practice it didn't seem to be of much use. I don't know if it was because of the lower light level or because the lens didn't focus slower to compensate for the increase magnification, but whatever it was, it seemed to have a really difficult time focusing. Even in bright light with plenty of contrast, the lens would just go from one extreme to the other, vary rarely ever finding the correct focus. So, even though you could get autofocus working, it was more or less useless.

Pins to reenable autofocus

On the other hand, using the new live view mode (available on the newer cameras) with its new contrast based focusing, autofocus worked like a charm with either teleconverter (or even with both on at the same time). This was a very pleasant surprise.

Speaking of attaching both teleconverters at the same time, this too worked fine. However, due to the way the lens communication system was designed, the camera would only detect the teleconverter that was closest to the lens. This means that only one teleconverter will be reported in the EXIF data, and the reported aperture will only reflect that one teleconverter. Putting both the 1.4X and 2.0X teleconverters on an f/4 lens will turn it into an f/22 lens. However, the camera will report it as either an f/5.6 lens or an f/8 lens (depending on the order of the teleconverters). This also means that if you put the 1.4X closest to the lens, you can still use the regular autofocus with an f/4 lens (though just like when you trick it by taping the pins, regular autofocusing isn't very reliable using this method).

In short, everything about the way the teleconverters were designed and functioned was excellent, and behavior was exactly what you'd get from the Canon teleconverters.

Image Quality - Test Methodology

In order to test the image quality of the teleconverters, I ran them trough a number of tests. Each test was done using my best lens...a Canon 70-200mm f/4.0L IS. In every case, the lens was used 2 stops from wide open, which is about where the lens performs best. This resulted in an aperture of f/8 with no teleconverter, f/11 with the 1.4X, f/16 with the 2.0X, and f/22 with both teleconverters used together. In each case, I adjusted the shutter speed accordingly to compensate for the smaller aperture, so that each test case ended up with the same exposure level.

I picked 4 focal lengths: 200mm, 280mm, 400mm, and 560mm. These represented the maximum zoom you could achieve when using this lens with neither, either, or both of the teleconverters. I then shot at each of the 4 focal length using all 4 possible combination of teleconverter magnification: 1.0x (no teleconverter), 1.4X, 2.0X, and 2.8X (both teleconverters). When shooing at a focal length that was less than the maximum achievable (such as 200m when using the 1.4X teleconverter) I zoomed out the lens as necessary to get as close as possible to the desired focal length (ie: setting the lens to 144mm and adding the 1.4X gives the same magnification as 200mm with no teleconverter). When shooting a focal length that could not be archived with that combination (such as 560mm with neither or just one teleconverter), I simply took the largest magnification available with that combination and resampled the results to approximate the more powerful focal length.

Image Quality - Test Results

On the surface of it, I learned exactly what you'd expect. In any case, no teleconverter is better than the 1.4X, the 1.4X is better than the 2.0X, and the 2.0X is better than the 1.4X+2.0x used together. In other words, if you can get the composition you are after without using a teleconverter, then you are best off not using it. It's better to use the lens at 200mm with no teleconverter than it is to put on the 1.4X and then zoom out to 144mm or less. In such a case, you are better off removing the teleconverter and zooming in.

Comparing the results of no teleconverter to the 1.4X was very positive. There was a significant improvement in detail compared to simply resampling, and the loss in contrast was minimal. There was very little tradeoff here, thus the choice of using the 1.4X when needed is pretty much a no-brainer.

When comparing the 1.4X to the 2.0X, the decision was more difficult. There was a slight improvement in detail, but at the expense of a noticeable decrease in contrast. Combining the teleconverters gave an even slighter (barely noticeable) increase in detail compared to the 2.0X alone, with an additional loss in contrast. Thus, in contrast to the 1.4X being a no-brainer, using the 2.0X teleconverter (or using both together) takes a bit more careful consideration.

Below are the test results. Click each image to go to the full size images.

200mm test

280mm test

400mm test

560mm test


I'm quite happy with the results. The improvement seen with these teleconverters is quite reasonable, especially given the price. I'd have no trouble recommending the Tamron teleconverters to anybody.

Of course, the real question is: how do they compare to the results from the Canon teleconverter? That will be subject of my next review, which will hopefully be ready by tomorrow.

UPDATE: I've posted a followup comparing the Tamron and Canon teleconverters and found them nearly identical. As a result, I'm very satisfied with the value of the Tamron teleconverters, and I highly recommend them.

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