Ok, so, Christmas is approaching (!!) and I am considering some additional lens to buy.

And, I was just curious to know what's the story with Canon's green circled lens: Canon EF 70-300mm f/4.5-5.6 DO IS USM .

I am not really considering that, actually, as I am looking more into wide angle ones (16-35 would be the ideal choice, but it is very expensive. 10-22 seems great and more affordable), or some Macro lens, but still, I am curious on what's the story with the 70-300 "green".
What is the meaning of the Green versus the Red for the "L" series, if there's any?

The Green lens, or 70-300mm DO-IS, is built to the same quality as any "L" series lens. So consider "DO" to be equal to "L" in all materials/construction.

But.. the DO is much smaller than one might expect for a 300mm zoom with a f4.5 aperture. This makes it a great travel lens -- eg. it was in my camera bag when we visited you folks in 2008.

The way it gets to be small, is by using a very special fresnel lens (DO = Diffractive Optic) as the main element. This is an element with zillions of finely etched concentric rings, similar to the flat magnifying "lenses" that many of us keep in our wallets or purses. Instead of bending the light like a normal lens, it instead uses a diffraction effect to achieve a similar thing in less space/weight.

The downside, is bad bokeh. Instead of a nice, beautifully blurred background, some of the circular blurs have bulls-eye centers. This is a problem for some photographs, and non-existent in others.

I'll see if I can find some examples of it from our Italy-2008 photos.. later.

Cheers

On a related note, here (gzip'd and attached) is the EXIF summary data from our Italy photos. I try to review data like this after each major trip, because it tells me many things about the suitability of the photo gear.

Eg. which lens I use the most, which focal lengths are used, etc.. If, for example, I notice that I'm constantly using the 17-85mm lens at the full 85mm setting, then I know that I really ought to have a longer lens in the bag.

It was data like this that got me to purchase the 10-22mm lens --> I noticed that whenever we traveled with the 16-35L or 17-85, there were tons of photos taken at 16mm or 17mm with those lenses. TONS of them. This told me that I really needed/wanted a wider lens.. thus the 10-22mm.

Cheers

As I recall, the "bulls-eye bokeh" effect happens mainly when shooting "into the light", and is rarely seen otherwise. So as a habit, I avoid shooting into bright light with this lens, and don't have many examples.

The lens is tack sharp in normal use. So here, I'm making a list of samples, and will be editing this post with new ones as I dig through the collection.

These first ones, show just how sharp this lens can be in dark light, wide-open, with good bokeh, no tripod.

Spiked Lamp.
Lonely Lamp.

The Raw original files look every bit as good/bad as these reduced size jpg images.
Here's the only example I've found that has even a hint of the bokeh issue: Garden Statue.

And here is a 100% crop of the background from a JPG created from the raw file. If you pixel-peep in a good image viewer, you just might see a hint of the tiny bulls-eyes. Or not.

Cheers

This photo, from the same collection, shows more of the type of photo I use the 70-300DO for when travelling. Close-in detail shots.

Mark,

Thank you so much. This is excellent information, and now I AM actually considering the green lens. I did not think to examin my exif data to find out what lens I would end up using more. After all, I just bought a reflex. Still, I am going to start analizing my shots to form an idea also based on data rather than just on "feeling".


P.S.: I can't see the bull-eyed centered blur.

P.P.S.: Mark, the .gz file you attached seems to be currupt or only partily there. I get an unexpected end of archive error. Size on my disk after dload is 26,596 bytes.

So, thinking about the DO lens, Fresnel Lens is a pretty old device/concept in physics.

I am guessing that the reason why it has been used for camera lens only recenty is that the number of fresnel rings needed not to compromise image quality is quite high (you mention "zillions", Mark), ergo "difficult" to build... ?

Indeed, it is really cool that a 70-300 can be so small. It is shorter and lighter than the 24-70L .

I wonoder if the f/ (quite higher than 2.8) is also affected by the fresnel lens, and if so, how...

Fresnel lenses don't operate on diffraction. They operate on the same concept of refraction as a normal lens. They just remove the mass of glass away from the curved edges that don't provide any additional refraction, and then collapse the edges towards each other.

Diffraction usually refers to interference patterns that may or may not be due to some level of refraction.

The "DO" label on this lens stands for "Diffractive Optics", and that's how it works according to Canon (diffraction). The fresnel likeness is how I prefer to describe it in laymans terms. Except this lens has little grooves on such a teensy level, they really do operate diffractively (is that even a word?).

My memory is improving a bit now, and the prime weakness I have with this lens is indeed when shooting towards bright light. Blue sky is fine, but towards the sun is difficult. The lens tends to put bloomy halos around bright spots, like the light leaking through the treed background in the sample crop above. Things get washed out easily when shooting towards very bright light.

Me, I use it to pick out architectural details mostly, but also for long distance shots -- being careful to shoot away from bright sky rather than towards it.

Cheers

This lens has a quite small front element diameter, with a small lens cap to match. Thus the f-stop range of 4.5-5.6: the opening at the front only lets in that amount of light. Not enough light for f4 or f2.8 etc.

Cheers

Okay, reuploaded it. Try again? The current file is 26611 bytes log, and gunzips to 315490 bytes. No CR chars, so use WordPad rather than NotePad when viewing on MSWin.

Cheers

This photo.net article gives a pretty good review story for the DO lens.

And here is a brief but informative page from Canon themselves.

I am guessing that if a fresnel lens has a high enough number of fresnel rings, then you may have diffraction patterns as well due to the rings very close edges. Maybe that's what Canon is using/referring to?

Edit: Photo.net article seems to give a different explanation, which I don't fully understant yet.

Size on disk is now ok, but it does not unzip using 7Zip or Winrar. I downloaded both with Chrome and IE. Weird. Usually both archivers owrk well with GZip.

Okay, here's a .zip version for the cripples.

Okay, the Canon link makes sense, and it is diffractive, but the reason that it saves weight is far different from the reason that a Fresnel lens saves weight.

A Fresnel lens trades optical linearity for a reduction in mass.

The DO lens reduces weight by swapping out the second lens of a doublet (a pair of lenses that are intended to reduce chromatic aberration), which is usually a biconcave lens with a different Abbe number from its pair, for a concave-convex refractive lens that actually has a negative Abbe number.

You can see how switching from a biconcave lens to a meniscus lens gets rid of a significant amount of mass.

I was not clear. Both RAR / 7ZIP do "open" the archive, but they report a broken file inside, and then do not extract it.

Now I can extract the .txt file inside, but it looks like a binary and not a txt file. Not a unix-dos issue. *nix text files are handled fine with textpad (or others) in Windows.

Can't zip a file under Linux?!

In any case, I don't want to waste your time on this. If it's my issue here on the win boxes, I'll sort it out later.

Yes, there's no fresnel lens in there, I seem to understand.

EF 70-300mm f/4.5-5.6 DO IS USM sells for 1100 Euros here. 700 Euros for used ones from some eBay Top Sellers. Would you guys buy a used lens on eBay?

Both Mark's files (.gz and .zip) contain a gzip'd archive named italy_2008_exif.txt. You will need to extract this file, rename it to something.gz and then extract italy_2008_exif.txt from it.

Ok. I'm an idiot. Sorry. That worked obviously. Thank you.

Oh, duh! Okay, I goofed with the double gzip!

Thanks Rod!

It doesn't actually save (much) weight. This is a dense, heavy feeling lens. But it is short, small, and fits neatly into the camera bag!

I bought a used, 60mm EF-S macro lens off of eBay. Got a good deal (60% of new) on a 10/10 condition lens.

Tack sharp, couldn't be happier with it.

But..

When I purchased the 70-300DO, new, from a dealer, I inspected all three copies that he had in the store, and one was ever so slightly, but noticeably, worse than the other two. I am very happy with the one I picked from those three.

Cheers

Did you? I often faced the same issue when de-compressing gzips, I assumed it was RAR/7Zip/WinZip/whatever sw I was using to occasionally wrongly deal with those. That's why I was naive not to think about it this time.

In any case, just to analyze your data, which is an interesting exercise for a newbie reflex owner like me trying to decide what lens to add to my newly started collection, I see this:

I wonder whether a lens is something that can "easily" be damaged. I am thinking of scratches, fo course, but the ones I saw in eBay so far are "guaranteed" not to have scratches, and can be returned. A used 70-300 DO is interesting. It is not a bright lens, but it is well built and reaches 300mm. It is a very good zoom for a learner like me, and couples well with my 24-70. And € 700 is withing my budget. Mmmh...

Just remember that it is pretty bad when shooting towards very bright light, and great otherwise.

The image quality is good, but nowhere near your 24-70L.

Yes. See, I don't see me buying a 70-200 L series of any type any time soon, given both price and size. It's a lot of moeny and I would hardly actually carry it around. From this regard, a used DO is interesting...

Yeah, I have a 70-200IS-L f2.8 here as well.

It does get carried along on some trips still, but the 70-300DO has supplanted it for overseas travel now.

The image quality of the 70-300 is not even close to that of the 70-200. I would not choose the 70-300 for portraits (the 70-200 wins big time there), but it is still very good for our travel photography.

Cheers

If they have no scratches on the lens, and no severe gouges on the body, then it's pretty difficult for there to be damage elsewhere.

One thing to look at, is whether the internal lubricants have leaked, smudging the internal glass elements and/or aperture blades. This was common with really old (1970-1980s) lenses, but I don't know if it still happens.

It comes about as a result of improper storage -- lens on its side, in hot conditions, rather than lens standing up in cool conditions.

The only real concern I have with used, recently made lenses, is that they may not be the sharpest ones available. Like I said, my own 70-300DO was hand picked by me from the three the dealer had on hand. One of the others was visibly worse when used on my own camera body (20D), and the third was probably equal to the one I bought.

Canon's quality control on highmedium-end lenses does not impress me (nor many other folk).

Cheers

A good way to check for lubricant transfer (usually from the helicoid) is to put the camera on the body and do a long exposure with the aperture set to f/16. Check and make sure the aperture blades are free of oil- any oil at all could make the aperture blades get "slow" over time.That would manifest itself in Error 99's on EOS lenses I think.