Canon’s new 600mm and 800mm lenses

Started 3 months ago | Discussions thread
AiryDiscus Senior Member • Posts: 2,139
Re: Canon’s new 600mm and 800mm lenses
2

Chris R-UK wrote:

martinhb wrote:

Here's an introductory article about dual layer diffractive optics from Canon :

https://cpn.canon-europe.com/content/education/infobank/lenses/multi_layer_diffractive_optical_element.do

Thank you. That explains very clearly how the diffraction elements are used. If I read it correctly, it would seem that these elements are used in the same way as in the 400mm f/4 DO and the 70-300mm DO ( which I used to own). I assume that the Nikon 500mm PF uses them in the same way.

Yes - same tech within Canon.  The 70-300 is single layer, but the 400 is dual layer.  Nikon PF is a different type of diffractive optic, but the fundamental idea is the same.

When I bought my 70-300mm DO, it was more than double the price of the non-DO version of the lens, although it had somewhat better build quality. At the time it was implied that the use of DO elements increased the price but reduced the length. Maybe that was just Canon marketing.

That's correct - polishing glass is expensive, but is very cost effective.  The traditional machines are very cheap, polish huge volumes at a time, and cost peanuts to operate.  You can't polish DO, because of the sharp faces.  I would hazard a guess they might have diamond turned all of them for the 70-300, based on its time in history.  That is quite expensive, one part at a time on a $200k machine instead of, say, 16 at a time on a $2,000 machine.  I assume for the 400/4 and these that they are molded.

The Nikon 500mm f/5.6 is four times the price of the 800mm f/11. Can the larger front diameter of the Nikon and better build quality account for all that difference? Maybe it can.

Yes on size.  The scaling of price for optics, at least in small quantity precision vendors, is worse than linear in area (i.e., something like area^1.25).

I think Nikon prints their DOs with a lithographic stepper.  Semiconductor processes scale well, but I can't imagine that's as cost effective as injection molding and bonding, which is what Canon does.  I could be totally wrong on how they do it, but that's a decent educated guess.

I can’t imagine that removing the diaphragm mechanism has a huge effect on the price. Does a fixed aperture enable a simplified lens design to be used?

No, it doesn't simplify the lens design.  My guess is that they use the front element as a stop, much as a telescope, so there is no stop at all (could be wrong).  I don't have access to order sheets for tens of thousands of them, but the replacement cost price for the diaphragm in the 400/2.8 is $437.  It's about two inches in diameter.

Maybe the very low prices of these lenses come down to build quality and an expectation that they are going to sell in large quantities compared with, say, a Canon 800mm f/5.6.

I think you cannot write off build quality so casually.  They aren't conventional, and by looking different you may assume they are worse.  Canon knows how to put together a lens.

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