EF 70-300mm DO IS

Everything you always wanted to know about diffractive optics*
* But were afraid to ask

We assume (although we may be very wrong) that you were asleep during not one but the whole set of physics classes in High School, and in one of those naps you missed a couple of important optical concepts. It's time to wake up and pay a little attention since Professor Otto A. Fishonado will educate us to understand the EF 70-300mm DO IS (DO=diffractive optics IS=Image stabilizer) lens:

"Well, dear students, I am sure that you are familiar with a little thing in a credit card called a 'hologram'. You may also have spent quite a time mesmerized by the beautiful rainbow created by a Compact Disc. Have you ever seen a bright ring around the sun or the moon? All those are examples of diffraction. Diffraction is associated with wave propagation such as bending, spreading and interference of waves passing an object that disrupts the wave. Although it occurs with any type of wave (such as sound waves or water waves) it is very noticeable in electromagnetic waves such as light.

Professor Otto A. Fishonado Doctor in Physics

Francesco Maria Grimaldi (1618-1663, Italian Mathematician)

Francesco Maria Grimaldi was the guy that paid attention to these phenomena for the first time and called it diffraction, from the Latin diffringere, 'to break into pieces', referring to light breaking up into different directions. The closely spaced tracks on a CD act as a diffraction grating to form a rainbow pattern. This principle can be extended to create a grating with a clearly visible structure (the case of the credit card hologram.)

When you see the rainbow in a CD you are seeing the light broken into pieces (diffracted). A glass lens refracts (bends) the light waves as they pass. With multiple elements it is possible to keep the waves focused instead of spreading in the rainbow. If a lens has a diffraction grating (such as the the closely spaced tracks on a CD) with smaller intervals toward the edges, then it is possible to solve some of the physical limitations of camera optics.

.Canon EF 70-300mm DO IS close up. Notice the diffraction grating.

When a diffractive element is combined with other glass optics the final result is a corrected image without chromatic aberrations and an improved image. And a good result from this process is a lens with reduced size and weight and, theoretically, a higher image quality than a comparable focal length lens that uses conventional glass optical elements." That's it for Professor Otto A. Fishonado (thanks professor!)

The Canon EF 70-300mm DO IS is the second lens in Canon's line to incorporate a diffractive optics element. With such an important innovation these class of lenses deserved their own signature: a green stripe around the lens.

The construction of this lens is superior. A combination of poly carbonate and metal provides a sturdy and durable lens. It is not an L lens but it is clearly better than the conventional Canon glass.

Although this lens is smaller it is not much lighter. For the photographers on the move it is great to have such a compact lens with a very respectable focal length of 112-480mm (35mm equivalent) when used with a sub frame camera.

The quality construction is remarkably good. Everything works smoothly. The zoom ring has a lock at 70mm for convenient transportation.

A photographer doesn't need to understand the concept of diffraction to appreciate a long tele photo lens that is more portable. The 70-300mm DO is smaller compared to other lenses in the same focal length, but it extends quite a bit.

The Image Stabilizer is a must in such long focal lengths. The ultra sonic motor is, as always, fast, quite and dependable with very precise auto focus.

The lens includes a leather pouch and the lens hood. As you may know, Canon provides such accessories with top of the line lenses only. That may indicate you that the diffractive optics doesn't come cheap. More on the price later.

When we began shooting with these lenses knowing all the cool stuff about diffractive optics we were very excited. When we compared this DO lens with the Canon EF 70-300mm IS USM we felt something was wrong: everything was nearly identical. The DO lens was supposed to have improved contrast, less chromatic aberration and even sharper edges. But we found that both lenses have the same image quality. That's quite a surprise because the 70-300mm DO IS has a price tag of $1,150 versus the $550 of the Canon EF 70-300mm f/4-5.6 IS USM. Everything is the same in both lenses: maximum aperture figures, image stabilization (that works incredibly good in both cases) and even a lock to avoid the lens extending by accident. For almost twice the price you obtain a lens of comparable weight but smaller in size. Yes, construction is very good but that's not enough for such a high price tag.

After all the technical yada yada the DO lens was supposed to be an exciting glass, but everything seems to remain in the theoretical realm, since there is a little result on optical quality. You can achieve the same optical quality for much less money. No wonder this is just the second DO lens in Canon lens and since 2004 (when this glass was unveiled) there hasn't been released any other lens with diffractive optics elements.