The new 400 mm f/4 DO lens

[Edward1064]

Recently I have seen some very positive comments about the performance of this lens.  Does anyone have a reference that discusses its design in some technical detail?  The overviews for the market show a picture of what is called a diffractive optic, but which looks like a Fresnel lens, which made its name in lighthouses in the 1800s.  And I cannot understand how a circular diffraction grating can work over a broad range of wavelengths.  Diffraction gratings have historically been used to separate wavelengths, not combine wavelengths and beams.  It makes me wonder whether the word "diffractive" is just a marketing discription.  

Thanks for your thoughts on this.

Edward

[TTMartin]

Lenses: Multi-layer Diffractive Optical Element

[Edward1064]

Thank you for the link.  I had seen this before, and its sketches of the lens remind me of a Fresnel lens.  What matters I think are the (radial) dimensions of the circular lens elements. This could be a satisfying overview if it were filled out with some more  technical detail.  

I do understand that in a Forum like this one, many people have no interest in the technical details of cameras and lenses.  But for some of us understanding some of the engineering details can enhance the appreciation of these sophisticated devices.

Ed

[kvbarkley]

It *is* a fresnel lens.

http://www.kenrockwell.com/canon/lenses/400mm-f4-do-is-ii.htm

[TTMartin]

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@Edward1064 wrote:

Thank you for the link.  I had seen this before, and its sketches of the lens remind me of a Fresnel lens.  What matters I think are the (radial) dimensions of the circular lens elements. This could be a satisfying overview if it were filled out with some more  technical detail.  

I do understand that in a Forum like this one, many people have no interest in the technical details of cameras and lenses.  But for some of us understanding some of the engineering details can enhance the appreciation of these sophisticated devices.

Ed

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I'm confused what details you think are missing in that article short of Canon releasing trade secrets.

What specific question do you have remaining after reading the article?

The MTFs indicate it has superb image quality, including excellent contrast.

And Lensrental's Roger Cicala's tests confirm what the MTFs show. (see his January 27, 2015 blog post)

[Edward1064]

What is missing is all of the basic physics.  One cannot understand at a fundamental level how this lens works.  But, based on the performance testing, I do not doubt that the designers have done a fine job.  

[kvbarkley]

Just FYI, LensRentals has just made this lens one of the favorite products released in the last ten years:

https://www.lensrentals.com/blog/2016/07/here-are-our-top-ten-favorite-products-of-the-last-ten-year...