Wide-Angle Lenses Revisited

Introduction. Having used the Sigma 15-30 F3.5-4.5 on a Canon D60 for several months, it was becoming quite apparent to me that the lower edges of all my images, particularly those shot at 30mm, were never really sharp. The centers of my images were extremely sharp...even wide open. But not the corners.

So, I decided to revisit my earlier comparison of this lens with the much cheaper Tokina 19-35 F3.5-4.5 lens. Just for fun, I also decided to compare them both (at 30mm) with an old Canon 28-70 F3.5-4.5 zoom lens I have. (Note: The Canon lens is not the popular, highly regarded and expensive "L" lens, but an old consumer level zoom lens.)

All images were taken using a tripod, mirror lockup, self-timer outdoors in overcast daylight. I used a Perl Script to crop the corners and center of each image and create the table below. Based on my experience using these lenses for several months, I feel that these test images are quite representative of how these lenses perform on "real-world" subjects.

Results. My findings are consistent with my earlier results, but underscore just how weak the Sigma is at the bottom corners.

• Good news first: The center of the Sigma lens is very sharp...wide open it is the sharpest of the bunch at all focal lengths.
• Despite its sharp center, at 30mm, I'd say the Sigma is the weakest performer (easily beaten by the Canon and Tokina lenses, which each cost about 1/3 of the Sigma). The bottom left corner of the Sigma is very fuzzy even at F8. (I also tried F11 which looks about the same.)
• At 19mm, the competition between the Sigma and Tokina is closer, and there really isn't too much difference in terms of sharpness. The Sigma does win, however, in terms of barrel distortion. The Tokina is clearly inferior in this category.
• Because the D60 has a sensor smaller than 35mm film, the image corner crops shown here aren't from the periphery of the lens. I haven't tested these lenses on a full-frame digital or 35mm camera, but my guess is that Sigma would not do very well based on these images.

Conclusions. Same as last time. Unless you really need the extra width, save some money and go for the Tokina!

About the Image Crops. The image below was automatically generated using a Perl script that I wrote for this purpose. I decided that this script might be useful to others and have decided to make it publicly available here. I wrote the code quickly for my own use...so there are no guarantees, warranties, and you use it at your own risk!