We've created this page to talk about a couple of interesting things about the Tamron 15-30 and the Nikon 14-24 that we didn't feel were worth diving deep into in our main piece across the two the previous pages. We'll be talking about brightness differences between the two lenses, as well as what it took for optimum focus vs. optimum field uniformity for the two lenses.

Brightness Differences

We normalized the brightness of all shots to make comparisons easier, and when we were doing so, we noticed the significant amount of brightening the Tamron shots required relative to the Nikon shots at smaller apertures, but not at F2.8. Below, we've posted default ACR conversions of 15mm shots from both lenses wide open and at F5.6. No brightening or darkening or adjustments of any kind were made to these shots.

Compare overall brightness between the Tamron and the Nikon lenses at F2.8 in the rollover below, and you'll see little to no difference. Which may be in part to more vignetting with the Nikon. But roll-over from the Tamron at F5.6 to the Nikon at F5.6 below, and you'll note a significant increase in brightness in the Nikon shot. We measured approximately a half a stop, rather consistently, at F5.6.

Tamron 15mm F2.8 Tamron 15mm F5.6
Nikon 15mm F2.8 Nikon 15mm F5.6

It's not the first time we've seen differences in transmission or amount of light let through at any stated aperture (barring any brightening effects done by the camera when a particular lens is detected), but this was a bit on the more severe side than we're used to. In fact, in the sunset below, the Nikon shot achieved almost the same brightness as the Tamron shot despite receiving a stop less exposure (1/8s vs 1/4s). All adjustments applied were exactly the same between the two files, and shots were taken only one and a half minutes apart, so changes in lighting are not likely to be the sole explanation for the observed discrepancy. The trend continued at F8 and F11 as well.

We thought it interesting to note, and we'll be asking Tamron about it. As always, let us know your thoughts in the comments.

Tamron 15mm
1/4s | F5.6 | ISO 64
Nikon 14mm
1/8s | F5.6 | ISO 64

Focus Wide Open vs. at Shooting Aperture

The Nikon 14-24mm had to be focused at the selected aperture in order to get maximum sharpness at the focused (central) point, as you can see in the widget below. However, maximizing center sharpness ended up costing corner sharpness, especially on the left side. In our shootout on the last page, we chose the focus method - either focused wide open or at the shooting aperture - that yielded the best sharpness across the frame for each lens, and this cost the Nikon some center sharpness.

In other words, we couldn't optimize for both center and corner sharpness with the Nikon, which is why central sharpness on the Nikon suffers relative to the Tamron at F5.6 - but not when the Nikon is focused optimally for the central portion of the frame, at which point it catches up to the Tamron in the center.

The Tamron showed little to no variability in field uniformity and central sharpness depending on what aperture we focused at. To be frank, we're a little confused as to the causes for these differences, and will investigate further. In the meantime, we'd love to hear any thoughts you might have.