Diffractive Optics question

[Lardog888]

I've been looking for a lens upgrade (mostly to add IS or speed) for my 75-300 4-5.6 III, and have been considering the 70-300 4-5.6 IS, but I notice that there are two versions of this; one with DO and one without.  Seems like all the reviews are for the non DO lens, and I know nothing of this technology other than I can see that the lens is physically smaller and quite a bit more expensive.  Smaller might be nice, but if that's the only difference, taking cost into consideration, it's not for me.  I don't think I'd mind carrying the difference in size.  In fact, I also dream about the idea of owning an "L" lens (70-200 f4L, same with IS, and both the IS and non IS versions of the 2.8L), but I know this is a huge lens both in cost as well as size, and I'd never get a huge white lens past my wife.

Basically, my question is what are the advantages and disadvantages of the DO lens?

Thanks for the information.

[KeithB]

Here is a luminous landscape review of the DO:
http://www.luminous-landscape.com/reviews/lenses/Canon-70-300mm.shtml

[Bob Atkins]

The DO lens has two advantages, only one of them related to DO.

By using Diffractive Optics (DO), the lens can be made shorter then it would otherwise need to be. So if you want the smallest possible 70-300mm lens, the DO would be it.

In this case Canon put a real ring USM motor in the 70-300 DO lens, which means fast and silent AF, full time manual focusing and a non-rotating front element. Thi sis incidental to the use of DO of course.

One downside of diffractive optics is that when used wide open in bright light, especially on backlit sunbects you can get a soft "halo" arounf bright objects. DO cxan also result in some structure (rings) in out of focus highlights.

Overall, unless you really need the smallest (shortest) possible lens, I'd say the 70-300/4-5.6 IS id a better buy at half the cost of the DO lens. Though longer, it's actually kighter then the DO.

See http://www.bobatkins.com/photography/reviews/ef_70_300is_review.html for my detailed review of the 70-300/4-5.6IS

I also have a brief review of the DO lens (and comparisions to alternatives) at http://www.bobatkins.com/photography/reviews/70-300do.html

[henryp]

It might be worth noting that the Canon Zoom Telephoto EF 70-300mm f/4-5.6 IS Image Stabilizer USM lens weighs 1.4 lb (630 g) and is half the price of the Canon Zoom Telephoto EF 70-300mm f/4.5-5.6 DO IS Image Stabilizer USM lens, which weighs 1.6 lb (720 g). The DO is also 4.3cm shorter.