# Diffractive Optics



## Buszaj (Apr 11, 2008)

Hey everone, just wondering about diffractive optics. What does it do, why is it so expensive?

Thanks


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## Garbz (Apr 12, 2008)

It's a lens with an optical diffraction grating in the middle. The purpose is that it corrects the fact that light bends at different angles depending on their wavelength. 

This is called chromatic aberration (red / cyan) fringing on the edge of sharp contrasts when shooting wide open. And the Diffractive optics uses the principle of diffraction to correct it. 

Have a look at Canon's marketing material by doing a google search and it'll show you an example drawing of what this lens looks like. It should be pretty clear that this is an insanely hard design to cut and polish.


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## Alpha (Apr 12, 2008)

No offense Garbz, but screw Canon. Really. Screw Canon. They were one of the last manufacturers to develop an APO lens. Why give them so much credit for the technical aspects of building one?


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## JerryPH (Apr 12, 2008)

Holy crap dude, no one gave cedit anywhere. You asked a question, Garbz gave an aswer. If you do not like the answer, at least have the courtesy to thank the person helping you and keep your severely negative opinions to yourself.


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## Alpha (Apr 12, 2008)

JerryPH said:


> Holy crap dude, no one gave cedit anywhere. You asked a question, Garbz gave an aswer. If you do not like the answer, at least have the courtesy to thank the person helping you and keep your severely negative opinions to yourself.



Jerry, clean your glasses. I didn't ask the question. Someone else did.


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## Buszaj (Apr 12, 2008)

Alpha said:


> No offense Garbz, but screw Canon. Really. Screw Canon. They were one of the last manufacturers to develop an APO lens. Why give them so much credit for the technical aspects of building one?



Whoa, take it easy. Garbz did not say that Canon invented the idea, but that they have detailed drawings of all their lenses.


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## Alpha (Apr 12, 2008)

Just stressing the fact that this is hardly a proprietary design.


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## Garbz (Apr 13, 2008)

Jesus go get a massage and cup of tea or something and calm down. He asked about diffraction optics, not APO. Since he asked for the canon marketing term I told him to go to the canon marketing website where they can blow their own horn, just like if he'd has asked for VR I'd have sent him to Nikon's website, or IS I'd send him to Canon, or HSM I'd send him to Sigma.

I assumed he's a canon user since he asked for "Diffractive Optics"

I never said they invented it. Hell I'm a Nikon shooter, Canon users have big enough heads as it is


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## JerryPH (Apr 13, 2008)

Alpha said:


> Jerry, clean your glasses. I didn't ask the question. Someone else did.


 
Go take a valium. You were the one off the hook... and I do not wear glasses.


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## Jon, The Elder (Apr 14, 2008)

Well....that was certainly a pleasant little interlude.


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## usayit (Apr 14, 2008)

Yes it was...

Alpha should be especially embarrassed....

First... he read misinformation into Garbz post
Second... APO = apochromatic optics  
READ>> http://en.wikipedia.org/wiki/Apochromat
Third... DO = Diffractive Optics
READ>> http://www.usa.canon.com/consumer/controller?act=CanonAdvantageTopicDtlAct&id=2632

Two completely different technologies in optics......  APOs don't have diffractive grating in their glass elements.....


My limited understanding leads me to believe that APOs and DOs both control chromatic aberration but do so in different ways.  The "Canon Advantage" to using DO optics is that it can achieve good control over CA with less glass... which results in a compact and lighter package.   The compact and lighter package is the big selling point..... although I myself don't really care for DO too much.  I believe Canon (and many lens manufacturers) were employing APO type elements well before DO was even on the drawing board.


btw.. Do other manufacturers of lenses have an equivalent technology to Canon's DO?


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## Garbz (Apr 16, 2008)

Actually apochromatic optics is just the generic term used for correcting CA.

Sigma uses the "APO" technology and show the marketing department has no creativity what so ever, Nikon use ED coatings, and I believe Nanocrystal coatings also have an APO effect, Canon has DO and another I believe, but the principles are similar, bring light beams projected in different places through the colour spectrum to the same point.

The jury is out on whether this is best achieved by using a diffraction grating, or by using a coating that varies the refractive index, or what not. They each have their plusses and minuses. The obvious minus on the DO is the cost of producing the element is high.


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## astrostu (Apr 16, 2008)

As a small answer to the original poster - why it's so expensive - is because it's fairly new in the world of lenses.  Anything new usually is more expensive due to the R&D to get it out there and the new machinery to manufacture it.

Personally, I think it's too new to start investing in.  In other words, I think that diffractive optics -based lenses are still evolving and will be better, lighter weight, and cheaper in, say, a decade.


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## nicfargo (Apr 16, 2008)

DO = shorter barrel because of the way the glass bends the light, really expensive because it's new, and not as good of quality...but still pretty decent.


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## yeti (Apr 20, 2008)

DO = Diffractive Optics, as so many before you have already mentioned.

What this really means is that there is a diffraction grating embedded within the glass: a series of slits creating a grid with width in the order of the wavelength of light. Light hates being constrained in this fashion, so it bends and spreads, trying to fill the space behind the grating. This effect is different for the different wavelengths of light, but as it turns out, that counters most of the optical artifacts from a purely refractive optics, meaning that things like chromatic aberrations and various distortions are next to nonexistant. It also allows a lens containing a diffraction grating to bend light a lot more, eliminating the need for more elements.

Image-quality-wise, however, things are not all good: there is slight softness in parts of their image. I am not sure what causes it, but my guess is waves of like wavelengths following paths through different slits interfering with each other, producing interference minima. Maybe if Canon creates an EF-S DO lens, things aren't going to be nearly as bad, and stooping down the lens will probably also help (I haven't handle one, so I don't know) but as far as I can see the idea is largely abandoned now. Most people on this forum tend to believe that it compromises image quality too much. 

It's still a nice idea, though. I hate seeing it go nowhere.


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## Buszaj (Apr 20, 2008)

So what are the current best uses for these lenses? Or are they still trying to make them better?


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## yeti (Apr 20, 2008)

Noone really knows, it is probably waiting on some more research.

I know that Canon has a 400mm prime lens that has diffractive optics, which I hear isn't bad at all and is used for bird-watching and stuff. I know there is also a 70-300mm DO lens, whose main virtue appears to be its size and doesn't really have a well-defined target audience. Both lenses appear to have been released in the 90's, though.

I haven't heard of any recent such lenses, which doesn't mean that someone isn't working on them somewhere. I personally think it's a pretty cool idea and such ideas have a way to come back again and again until something even better replaces them. One way or another DO is probably going to come back. Even if Canon has had enough of DO lenses, Sigma, Tamron or Nikon might suddenly pick up the ball and start making DO lenses of their own. They might even be better than Canon's, given the new materials invented since the 90's such as certain nanomaterials that might potentially make a fine diffraction grating.

The problem with DO lenses is the softness they exhibit and their price. If someone comes up with a finer diffraction grating to embed within the glass, and/or a way to get that softness outside of the image circle in some way and/or a cheaper way to manufacture them, we are going to see a big comeback of DO lenses.

I personally wouldn't mind giving one such lens a shot, but I am one of those  people who will go head-first with everything new.  [/me eyes his router running a highly experimental firmware]


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## Mav (Apr 21, 2008)

Here's a review of Canon's 70-300 DO

The biggest advantage is the tiny size.  It's only 4" long fully collapsed and about 6" long fully extended at 300mm.  In comparison a typical non-DO 70-300mm lens is more like 6" fully collapsed and maybe 9-10" or even a foot fully extended!  So it's a big 300mm lens without really looking like one.  It's over $1000 though.  I might use something like this if I wanted to get tight headshots of people in crammed nearly standing room only spaces where you might not have room for a foot long lens, and also might not want to alert someone that you've got a big giant lens pointed at them which might disturb them and then ruin the shot.  So the stealthiness of this thing would be great.  I'm not a Canon shooter and don't hang out on any dedicated Canon sites, so I've never seen any real-world use examples and shots from those that have them.  I'd be curious to see what people do with these things and what it lets them get away with.


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## Garbz (Apr 21, 2008)

OH **** ******** *** Ken Rockwell has the same watch I do!

Need a new watch now!


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## Mav (Apr 21, 2008)

LOL Garbz.  You know what they say, birds of a feather, great minds, etc...


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## Garbz (Apr 21, 2008)

uke:

If I could through something at you through the internet I would! I'm sure you don't need to search for posts I've made which include his name. Mind you I'm sure you'll get the same posts if you search "babbeling idiot".

http://www.photozone.de/Reviews/Can...0-300mm-f45-56-usm-is-lab-test-report--review On a more technical review I would not be willing to spend near $1000 for that kind of resolution regardless of how small this lens is, especially if there's a perfectly good one available for half the price.


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## Mav (Apr 22, 2008)

Ok in all seriousness, if you've just noticed _NOW_ that he has the same watch as you, it tells me that you've basically never read hardly any of his reviews.  He posts that same watch macro shot in almost _every single one of them_, and thus you probably aren't one to be criticizing anything on his site considering you've never really read it.  I really have no clue what so many people's problem with him is on forums like these.


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## Garbz (Apr 22, 2008)

Lol believe me I've had this watch for a while and his looks reasonable new. I have read enough reviews to know I now avoid his site like the plague. The reason being when his site isn't loaded with hearty fanboyism, pure equipment ****, or other opinionated reviews, then it's loaded with miss-information.

Some of my favourite ever comments on his site include:
- No photographer would ever need a modelling flash. (I have no idea where he pulled this notion from)
- The SB-800 takes longer to cycle than the SB-600 (after firing both at full power. Well DERR the SB-800 puts out more juice. That doesn't make it the slower flash)
- The 80-200 AF-S is useless because of it's flare (said after he admitted to never using the damn lens)
- Colour management is a waste of time. (while claiming he's worked on the first colour managed systems)
- Not to read anything into the colour of his mass wide zoom lens review because he took the shots on different days (great now how do we compare the lens coating if not by the colour)

The list goes on. His site is just way to subjective, and loaded with reviews of products he has never used, or rates entirely on his opinion which he believes to be the only opinion in the world.

Mind you that's not to say that all of what he says is pure crap. Just to take most of it with a grain of salt. Keep in mind that most of the stuff on his site is an opinion. Rarely does he produce things that are objective. Even his test on photographing a brick wall and seeing how much distortion correction he applies in photoshop is a poor way of something that should be done by software using a distortion target.

Given how many good resources there are available on the net it's a shame that he ranks so high on google.


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## Alpha (Apr 22, 2008)

Moot point. 

DO _is_ APO. and APO is APO. The designation doesn't intrinsically say anything about the lens construction except that it prevents or reduces chromatic aberration, whether this is done by coating or diffraction or what have you. 

The whole thing just makes no sense except from a marketing standpoint. Why re-invent the APO wheel? It certainly doesn't make much sense from a practical or an R&D standpoint. Pit a german APO lens against a Canon DO, _at best_ the DO performs as well. Canon would have been served just as well to copy a german or japanese APO design instead of blowing their R&D budget on cramming a diffraction grating into their glass. After all, the marketing pitch is all about technology hype, and given that "APO" hasn't made it's way into pop lens consciousness, I bet they would have been at least as successful introducing it into the world of techno-whores with a more proven design.


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## Mav (Apr 22, 2008)

Garbz said:


> Lol believe me I've had this watch for a while and his looks reasonable new. I have read enough reviews to know I now avoid his site like the plague. The reason being when his site isn't loaded with hearty fanboyism, pure equipment ****, or other opinionated reviews, then it's loaded with miss-information.
> 
> Some of my favourite ever comments on his site include:
> - No photographer would ever need a modelling flash. (I have no idea where he pulled this notion from)
> ...


Would you like a tissue?  I think a lot of the Ken bashers just need to get over it and MoveOn.org, personally.

I just checked out your point on the SB-600 and 800 and you're wrong.  He states in more than one location that the 600 only re-cycles faster because of less power and that they're about the same in normal use.  So go "DERR" yourself for not reading. (link)  Since I can't trust you to actually go and read his site, here's a direct quote.



> 13.) The SB-800 has more power for each full-power pop so it's supposed to take longer to recycle and give fewer of them. In real TTL use this is irrelevant, since they both will give the same life and recycle times with the same output for each shot as determined by the camera's TTL system.


Stop bashing.  Start reading.  It's there.  Next?


I also checked out your point on the 80-200 AF-S.  He says right in the review that he _OWNS_ the lens and has so for years and never ceases to be amazed by the quality.  It's just useless for sunrise/sunset shots because of the flaring though.  Bummer.  I think he uses his 80-400 more for that.  Anyways, how could you get that he doesn't actually use the lens from that?  Not reading again? (link)



> I'm going to poke a lot of fun at my 80-200 AF-S here, but remember that this is probably the sharpest zoom Nikon has ever made and it works like a dream. Don't let my whining distract you. It is one of the sharpest lenses I've ever used, zoom or not, period. *It consistently delivers fantastic results that continue to impress me even after using this lens for five years.*


Right.  Using the lens for 5 years = "never using the damn lens". 

I swear, if I got a dime for everytime a Ken basher said something about the stuff on his site that didn't exactly add up, I could quit my day job! 


I see all these comments about "he's never actually used the lens" and then i see remarkably complete reviews on his site with plenty of OBJECTIVE tests like distortion where his personal opinion really isn't going to change the results.  Nit-picking about the specific way he tested color (didn't seem to hold up by the way) or how he actually tests distortion?  Sheesh.  Geez the walls look flat after correction don't they?  And the degree of correction is a good way to measure it against others is it not?  And he tests the same way every time, correct?  Don't see what's wrong with that...

And I still think it's hilarious that you just noticed now that he has the same watch as you.  Oh his is NEW?  Yeah whatever.  I've been reading his site for 2+ years now and he's used that same watch to test close focus performance for every lens he "hasn't reviewed".  In fact I'm so familiar with that watch now that I don't even need to read that section - I can tell just by looking.  "_ooooh, that's close and sharp. Nice!_"  Or... "_wow that sucks, not even very close either._"  A prime example that the people bashing Ken and his site don't even read his site to begin with and thus have no clue what they're talking about. :lmao:

Sorry man, but I could put together a better gripe list on inconsistencies I've seen on his site than you could, and unlike yours, mine will actually HOLD UP if you check them out!  How do I know?  Because I actually _read_ his site regularly and would be one to know, unlike the vast majority of the Ken bashers!  Who's spouting "mis-information" again?  

I like Ken and his site and have no clue why so many people get so upset about what he says.  Clearly many have not even _read_ what he said in the first place though.  Personally I never take advice from people who have very strong opinions about things they clearly know nothing about.  I place the astericks and "take like a grain of salt" warnings _on them_ and not on Ken.  It's very easy to "fact check" people claiming things about Mr. Rockwell and unfortunately your post is about par for the course when it comes to Ken bashers.  Hardly accurate and filled with "mis-information", the same thing you accuse Mr. Rockwell of.  I've learned a ton from it and have picked up a lot of great tips and advice.  Do I follow all of it?  No.  Do I take all of his advice?  No.  Why not?  Because I have split needs between doing baby/family photography and the actual landscape/scenic stuff that I really enjoy, and have to spend money accordingly.  He says right on his site in the ABOUT section that if you have a different style of photography than someone then you might not want to take their advice and might want to seek out someone else's advice instead.  So that means he thinks HIS opinion is the only one that exists.  Yeah, OK. :thumbdown:

It's a great site.  There's lots of good stuff to learn there.  Telling newbies to never go there or even more insulting telling people they'll never "get smarter" until they stop reading his site is piss poor advice, especially considering that the people bashing Ken seem to be factually challenged in the first place.  Just think twice about the advice if you have a different style or different needs is all I can say.  And he says that right on his site.  I've seen far worse advice given out on forums like these or from other photog sites than I have from Ken, but then again a lot of that has to do with your own personal style.  I like Ken's style and it matches my own when I'm actually doing his style.  And my results from my own testing match his as well (which he encourages you to do) so I trust him for other things as well.

Not going to say or read anything more.  It's irrational hatred is all it is.


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## Big Mike (Apr 22, 2008)

OK fellas...let's keep the pissing contests to a minimum!


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## Garbz (Apr 22, 2008)

Mav said:


> snip



Wow amazing you don't think that he corrects his site since 2005?

Look if you want to tongue kiss him that's your business. You asked me why I didn't like the guy I said it. Correcting his past mistakes is no excuse for delivering the false jibbering in the first place. I did read his site when I first was looking at the SB-800 and the 80-200 or I wouldn't have notice the problems. From then I gave up on him. Irrational hatred? No missinformation was too much on the few pages I have read on his site.

Maybe I haven't noticed his watch because I could never bear to read to the end of most of his reviews. I don't know, either way it's a free world. You're free to love him, I'm free to find sites I feel offer more objective reviews.



			
				Mav said:
			
		

> I swear, if I got a dime for everytime a Ken basher said something about the stuff on his site that didn't exactly add up, I could quit my day job!



Now I wonder why that is. But don't attack me personally if there are clearly plenty of people who agree with me.

Btw I found it funny that you went to read through every page with every comment I made just to prove me wrong. MoveOn.org is a good suggestion. Practice what you preach.

/EDIT: Btw you were right. He never used the AF version not the AF-S version. I mean he's got a review that says "I don't know if it suffers from the flare problem" Wow did he try it maybe? Shoot at the sun or a light in the room? Interestingly he didn't photograph his watch with it either. Maybe have a look at his 600mm f/4 review where he produces gold such as saying he has never tried it "but I'm sure it's a winner" Yeah I hate his site and his subjective reviews.


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