Equipment TestDrive: Tamron SP AF28-75mm ƒ/2.8 XR Di LD Aspherical (IF) Zoom
A new family of lenses that will help you make the leap from film SLRs to digital SLRs
The new Di series of lenses are Tamron's Digitally Integrated optics. They're designed to meet the performance characteristics of digital SLR cameras and image sensors. Like the other lenses in the Di line, the new SP AF28-75mm ƒ/2.8 XR Di LD Aspherical (IF) Zoom is optimized for a digital camera, but it will function fine on a film-based SLR body. If you've been thinking about adding a digital SLR to your gear and you want to keep it in the same system as your film camera or cameras (i.e., if you shoot Canon and you want to keep a fully integrated Canon system), lenses like the new Tamron Di models give you an opportunity to build a digital system that fully complements your film system.
The new Tamron 28-75mm zoom, when fitted to a digital camera, gives you a "normal" to slightly telephoto focal range. Obviously, this depends on your digital SLR's magnification factor. Other than the full-frame image sensors that are available on a couple of very high-end cameras, most D-SLRs have a sensor that results in a magnification factor around 1.5x, which makes this lens approximately equivalent to a 42-112mm ƒ/2.8. Note that the magnification factor doesn't affect the fast ƒ/2.8 constant aperture.
Working with a lens that maintains the same aperture when zooming in and out at ƒ/2.8 is very convenient in low light, and it's ideal for keeping depth of field to a minimum. Naturally, the ƒ/2.8 maximum aperture is great for action shooting because you can use a higher shutter speed. It also aids in both manual and autofocusing, and makes it easier to see the image in the viewfinder when composing.