Digital Lens
The Digital Photo Pro posting The Digital Lens Revisited asks the question
In a world of marketing buzzwords like “optimized” and “designed for digital,” what’s really going on behind all the hype?
Here are some highlights from the posting. Read the posting for much more detail.
Crop Factors
If you use a 20mm film lens to project an image on a sensor that’s 16×24mm, it will behave like a 30mm. This is because the sensor is 1.5 times smaller than a 35mm piece of film, which is 24×36mm. To maintain a 20mm focal length, you’d need a lens with a focal length of 13mm. D-SLRs with sensors even smaller than 16×24mm will need even shorter focal lengths because the magnification factor is even greater
(Credit: Digital Photo Pro)
Chromatic Aberration
Because lenses disperse the different colors of light, it causes them to focus at different points (Fig. 3). Telephoto lenses and wide-angles with an inverted-telephoto design are especially prone to this phenomenon.
(Credit: Digital Photo Pro)
Ghosting and Flare
Canon’s Westfall explains, “One of the big differences between a digital SLR and a film camera is the fact that you’re using this image sensor with usually a low-pass filter in front of it. And it’s a shiny surface. So if you’re using a lens that isn’t optimized for an image sensor, there’s a risk—depending on which lens—that there will be some internal reflections that bounce back and forth between the image sensor and the element in question, which could be any element in the lens.
“What we’ve done over the last seven or eight years now is to work on developing coatings and make sure that the shapes of the individual lens elements are such that the flare and ghosting are minimized or eliminated.”
(Credit: Digital Photo Pro)
Bottom Line
At the end of the day—beyond all the technical details of why and how—it’s about quality. What are the best lenses for your camera, either the one you own or the one you rent when you go in the studio or out on location? What will get you the best possible images when you snap the shutter? No amount of editing will ever make up for lack of quality at the moment of capture.
Lenses designed for digital capture have many advantages over analog lenses, to be sure. Not in every case—there are exceptions, as we mentioned. But there are some good reasons why everyone is making them now and why you should consider using them if you haven’t already.
…John
