See that lens up there? That’s Sigma’s upcoming 18-35mm F1.8 DC HSM | Art, which has the very awesome privilege of being the world’s first f1.8 standard zoom. Since it’s for APS-C bodies (Canon’s Rebel / XXD / 7D series bodies, and Nikon’s DX bodies) you’re talking an equivalent FOV of 29-56mm on Canon and 27-53 on Nikon. But, that’s just the FOV equivalence. What’s exciting here is the aperture. You see, depth-of-field isn’t reliant on the “equivalent” field of view, it’s a simple function of sensor size, actual focal length, aperture, and distance to subject. As a result, you’ve probably heard people talking about the DOF stops of disadvantage when using a lens on a crop body. Things like, “sure, it’s f2.8, but since you’re on crop that’s really more like f4.” That’s a sort of simplistic and somewhat wrong way of thinking about it, but the underlying concern is true. because we use shorter lenses for the same field of view on crop bodies then we do on full-frame, and because the shorter a focal length is the deeper it’s DOF is at the same aperture, you do see deeper depth of field on an “equivalent” crop body lens than you will on a full-frame one.
Enter the f1.8 zoom. Excited to see how the f1.8 would fare in real DOF comparisons, I broke out my DSLR toolbox calculator and ran some maths for you. I ran things for two bodies, full-frame and Nikon DX (1.5x crop). Then, I picked two focal lengths with the same field of view: 18mm on the DX, 28mm on the full-frame. I kept the distance to the subject the same at 2 yards. Then, I calculated for f1.8 on the DX, and f2.8 on the full-frame. The results? At 28mm f2.8 and 2 yards to my subject on full-frame my total depth of field was 2.3 feet. At 18mm f1.8 and 2 yards to the subject on DX, the total was 2.34 feet. So, Sigma’s f1.8 zoom here will let you APS-C shooters get the same shallow DOF we full-frame shooters get from those abundant f2.8 standard lenses we get for our bodies.
And, as a perk, f1.8 is still brighter than f2.8 by 1.3 stops. So, not only will you finally be able to get the same shallow DOF, but you’ll be able to do it at lower ISOs (which should help counter for full-frame’s low-light advantage, but that’s an entirely different discussion) or faster shutter speeds. Neato.
No words on availability or pricing yet, but this new Art series lens will be available for Nikon, Canon, and Sigma mounts.
If that sounds like your cuppa, head on over to our site to learn what little more there is and get your name on our list for your own copy of it. http://robertscamera.com/18-35mm-f-1-8-dc-hsm.html