![Canon Is Developing Lighter Supertelephoto Lenses [Rumor]](https://cdn.fstoppers.com/styles/large-16-9/s3/lead/2017/09/canon-do-lenses_jpg.webp)
Supertelephoto lenses are a love/hate relationship for a lot of photographers: they showcase some of the best optical engineering companies have to offer, but carrying them around is quite a workout. Canon is seeking to cut that weight with its supertelephoto lenses in development.
"Diffractive Optics" is the term Canon uses for Fresnel lenses, lenses that are often formed from concentric layers of glass, resulting in a sawtooth cross-section as opposed to the traditional smooth edge. See the diagram below, which showcases the cross-section of a Fresnel lens vs. a traditional design:
The beauty of the design is the same optical element can be made with much less glass, and in lenses where there's a lot of glass, that can translate the considerable weight savings. They also typically show better control of chromatic aberrations. Canon has demonstrated this with the 400mm f/4 DO IS II, which is lauded for its light weight and substantial optical improvement over its predecessor that consequently brought it into the true professional realm. The technology can also be seen in the 70-300mm f/4.5-5.6 DO IS lens. Now, the good people over at Canon Rumors are reporting that multiple DO lenses are being developed, with a release date in 2018. A 600mm f/4 DO IS was first seen in September 2015 at Canon EXPO, and it was an impressively small lens given the focal length and aperture. Such lenses would be a huge boon for those who have to lug these monsters around on the regular, namely sports and wildlife shooters. Head over to Canon Rumors for more.
[via Canon Rumors]
My main objection with Fresnel-based optics is its distracting flares. This is very annoying especially on lesser lit scenes with light sources in the background (streetlights, or the moon for example). I suppose they will address this with the design but am very skeptical about it.
Reviews for Canon EF 400 mm f/4 DO IS II USM are found easily enough:
This honestly addresses your topic concern, and others:
https://www.lenstip.com/509.1-Lens_review-Canon_EF_400_mm_f_4_DO_IS_II_U...
This seems even more positive on the flare issue:
http://www.kenrockwell.com/canon/lenses/400mm-f4-do-is-ii.htm
Short answer: Class A product, but do read and decide how you see it.
Implication might be made that Canon is going to do some fighting back via lens technology so you'll continue to see mostly Canons in the hands of sport pros for instance. If they up their tepid full frame bodies next round, they could dispel the currently popular idea they are slipping. Of course I own some Canon kit, so it matters to me:)
It amazes me how Canon (and most of its competitors, for that matter) seem to not be bothered with having their R&D guys cracking on, 24 by 7, on CURVED SENSORS yet!
I'd risk saying they actually seem to be content with being (once again) expectators to Sony and other mobile manufactures (mostly) to get there first!
The way I see it, it's not a matter of 'if" but actually "when" for such revolutionary technology to be part of our everyday lives - with lenses being then not only lighter, as they'll require less elements for CA correction, but cheaper and smaller as well. Even more so than with the currently promising DO elements.