A correct exposure is a simple combination of three important factors: aperture, shutter speed, and ISO. Since the beginning of photography, these same three factors have always been at the heart of every exposure, whether that exposure was correct or not, and they still are today—even if you’re using a digital camera. I refer to them as the photographic triangle. Read More »
The images below were shot using an EOS 20d, the lens set to f8 and focal lengths of
11mm, 13mm, 15mm and 18mm were used for the four shots shown.
As you can see, there is little, if any, distortion at the 18mm setting, but barrel
distortion increases as the lens is zoomed out to 11mm.
Of course distortion is relatively easy to correct if you are shooting digital. Most
image editing programs have some function to correct either barrel or pinchushion
distortion. The pair of images shown below show the correction of an image shot at 11mm
using JASC Paint Shop Pro 9.
Vignetting
Vignetting (dark corners) is very slight, even wide open at 11mm (f4.5). In fact I
can't really see any in the test images I shot. Below is a series of images shot of blue
sky at f4.5, f5.6 and f8. 11mm (17.6mm in 35mm terms) is so wide that I couldn't find a
shot where all 4 corners were blue sky, so you'll have to put up with just two corners. I
think it's pretty obvious that vignetting isn't an issue with this lens. As I metioned
earlier in this review, I also saw no vignetting with a normal thinkness Tiffen circular
polarizer, even at 11mm.
Below are the images shot at 18mm. There's maybe a hint of vignetting wide open at
18mm, it's hard to say. Whatever vignetting may be present, it's certainly not
significant.
The conclusion is that the Tamron SP AF11-18mm F/4.5-5.6 Di-II LD Aspherical (IF) shows
very little vignetting, which is commendable. It also does not vignette with a standard
thinkness polarizer, even at 11mm, which is good news too.
