There's been a lot of talk about the new Tamron SP AF 17-50 mm F/2.8 XR DiII lens on the various internet forums devoted to (digital) photography. At least in theory, the lens is an affordable alternative to the fast standard zooms sold by Nikon and other manufacturers (for approximately three times the price of the Tamron). But how does an affordable zoom lens specifically designed for DX (APS-C) size sensors perform at large apertures?
The image below shows the scene I used to test the lens. Not something you'd normally bother to take a picture of (unless you're particularly fond of suburban shopping centres), but it happened to be a convenient subject for me and to have enough detail across most of the image. For these shots, the lens was set to its widest setting (17mm; equivalent in terms of field-of-view to approximately 26 mm on a 35 mm camera), as this tends to be the 'difficult' end of the zoom range for lenses like these.
The red rectangles indicate the areas of which full-size (1:1) crops are shown below: The four corners of the image, plus an area located somewhere near the centre. The first set of crops, shown directly below, is from a picture taken with the lens fully open at F/2.8 and 1/400 sec. The camera used was a Nikon D50, set at ISO 200, "cloudy" white balance, and "normal" image quality. It was mounted on a Manfrotto tripod. With AF switched off, the lens was manually focused at infinity. Pictures were taken using the self timer.
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| F/2.8 | ||
Note that these are parts of an image that would be approximately 85 by 55 cm (33 by 22 inch) in size when viewed as a whole at this magnification (assuming 90 ppi screen resolution).
The second set of crops, shown below, is from a picture taken (a few minutes later) at aperture F/5.6 and 1/125 sec.
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| F/5.6 | ||
I'll leave conclusions about image quality to the reader. It's probably safe to say that the lens performs better at F/5.6 than at F/2.8 (as would any other lens), although the centre is already quite good at the widest aperture setting. Apart from that, it's up to the (prospective) user to decide whether image quality meets his/her needs.
Paul van Soest, November 2006
The images shown on this page were prepared using the command line tools jpegtran (for lossless JPEG transformations) and convert (part of the ImageMagick suite). Lossless crops of the selected areas from the original 6 MP (3008 by 2000 pixel) image were made as follows:
jpegtran -perfect -crop 320x240+0+0
[/path/filename.jpg] > ulcrop.jpg
jpegtran -perfect -crop 320x240+0+1860 [/path/filename.jpg]
> llcrop.jpg
jpegtran -perfect -crop 320x240+2688+0 [/path/filename.jpg]
> urcrop.jpg
jpegtran -perfect -crop 320x240+2688+1760 [/path/filename.jpg]
> lrcrop.jpg
jpegtran -perfect -crop 320x480+1024+640 [/path/filename.jpg]
> cncrop.jpg
The overview image shown at the top of the page was created using:
convert -antialias -resize 752x500 -fill none -stroke red -draw "rectangle 0,0 80,60" -draw "rectangle 0,439 80,499" -draw "rectangle 671,0 751,60" -draw "rectangle 671,439 751,499" -draw "rectangle 256,160 335,279" -fill white -stroke none -draw "text 270,490 'Tamron SP 2.8/17-50 mm: 17 mm @ F/2.8'" [/path/filename.jpg] ./28_crops.jpg
First published: November 12, 2006