Do??

DanielB

what does Diffractive Optics mean? i see it on lenses, does this make it better in anyway? :dunno

Blurmore

DO Optical Alchemy
DO is Canon speak for a technology which allows (mostly) telephoto zoom lenses to built smaller and lighter. DO uses concentric multi layered elements to effectively cheat on focal length. I'm not sure but I think it works much like a fresnel lens. Here is Canon's explain http://consumer.usa.canon.com/ir/controller?act=CanonAdvantageTopicDtlAct&id=2632

It also renders highlights in a characteristic donut shape many people find unappealing, similar to a catodioptric or mirror lens. The green ringed 70-300 DO IS f4-5.6 is a tiny lens for this focal length, but for 1200 dollars it doesn't produce L sharpness for an very L price.

pathfinder

DO optics allow smaller, lighter, more inexpensive lenses than standard refractive lenses.

DIffractive optics is a series of microgrooves on some of the lens elements themselves. Some folks comment about the bokeh of DO lenses, and sometimes they are objectionable.

Some folks do like DO lenses, including Uwe Steinmueller and Michael Reichman. Steinmueller likes and uses the 400 f4 DO IS - he calls it his 'pelican lens', for BIF shots. Reichman frequently uses the 70-300 DO IS - I think he likes the small, inconspicuous appearnce of it that belies its reach for candid shooting.

There have been rumors for several years that Canon was developing a 500 f4 DO as well. The standard 500 f4 IS L weighs about 8 1/2 pounds so lighter would be better. 8.5 pounds + a couple of pounds for a camera body and things get heavy really quickly.

I suspect the dounut bokeh that can be seen with DO glass, to a certain extent depends on the spacing of he diffractive lines on the optical surfaces and is less prominent in some lenses than others. I think the 400 DO may have less of this than the 70-300.