Tom, the original version of the lens is a "push/pull" zoom... a single ring serves both for focus and for zooming. Not my favorite design so I only borrowed and used it a little. Some people really like the push/pull design, especially for things like birds in flight, air shows, etc. The original version is about a half lb. lighter than the II, though it's still a fairly hefty lens.

The original 100-400 has quite good image quality... so long as you don't put any filter on it. For some reason, it "goes soft" when any filter is on there... even good, high quality ones. More than one person who felt the need to "baby" and protect it with a filter were stunned to see how much sharper it was when they removed the filter! I honestly can't say about how the II works with filters... I've been shooting with it for a couple years and have yet to need to use a filter on it.

Both versions of the lens use fluorite, along with some other exotic glass. They both also have fast, accurate USM. The original is one of five Canon lenses that require the IS be manually turned off when it's locked down on a tripod.... or the IS will "freak out". No problem like that with the II... it has some of the most advanced IS Canon makes.

The original lens' tripod mounting ring is more fully removable, reducing the weight for hand-holding it a bit more. In fact, one thing I didn't like about the II is the design of the foot used on the tripod ring, which is held on by a thumbscrew. I replaced that with a foot that Hejnar Photo makes for the 100-400 II and it's a significant improvement, especially for anyone using it on a tripod with a gimbal or on a monopod or anything else with an Arca-Swiss quick release system. RRS and Kirk Photo both also offer replacement tripod feet for the II, slightly different designs. These are largely unnecessary for the original version, though. A standard Arca-style lens plate can be used on it's tripod ring without problem, if needed.

The clearance pricing of the original is a very good value. There must have been a lot of them in stock around the world, it's still so widely available brand new.

Interesting the both Tamron and Sigma introduced 100-400s of their own, shortly after the Canon was intro'd. Both of those third party lenses are much cheaper... also a little lighter and smaller. However, they also are slower... the Sigma, in particular, is 2/3 stop slower than the Canon through much of it's range. I have not had any hand-on time with either of them, but it appears the Sigma may be a wee bit sharper than the Tamron... but either Canon is sharper still. The Sigma also doesn't have a tripod ring or means of adding one. The Tamron doesn't come with one, but there's an optional ring that can be fitted. Personally, I wouldn't want a 100-400mm that didn't have a tripod ring!

Please elaborate. Are you saying the III version is made for both versions of the 100-400L? When I read up on the version II lens, there was an indication that it was paired to the III version converter. When I read up on the earlier lens, I thought I saw where the II version converter was recommended............confused here. It may work with either. Could be the III works better but was not available when the initial lens was made??? If I do purchase a lens, I also want the best converter available for it. Converters, while not cheap are not nearly as expensive as lenses as you know. Any possible clarification is appreciated and thanks! Tom

I just received a new Canon 100-400L II today from Adorama. After opening the lens, I was looking at all of the sliders for stabilization, etc. and I noticed there is not a way to lock the lens for traveling. Am I missing something? The lens is not stable, as it telescoped out as I was putting it into the case. To be honest, I haven't even attached it to my camera, and I'm a little disappointed in it. There are raves over this lens, and I cannot imagine having to deal with the lens telescoping every time it faces the ground.

The version III converter was made for the newer lenses with the glass being designed to the newer glass in the new lenses. It is also said that the connections are better for all the electronic signals that go through from the body to the lens. Check the Canon info charts and see what they recommend as to what converter for what lens. The older converters could be stacked and if done right you could get great results, not so with the series III, you can not stack them because of the new design. I don't know if you could see any difference between a series II and a III with the naked eye. Either one would will fit, not a problem but if I was buying new lenses I'd be buying the series III, I have a 1.4 and a 2X both series III.

Please elaborate. Are you saying the III version is made for both versions of the 100-400L? When I read up on the version II lens, there was an indication that it was paired to the III version converter. When I read up on the earlier lens, I thought I saw where the II version converter was recommended............confused here. It may work with either. Could be the III works better but was not available when the initial lens was made??? If I do purchase a lens, I also want the best converter available for it. Converters, while not cheap are not nearly as expensive as lenses as you know. Any possible clarification is appreciated and thanks! Tom

Please elaborate. Are you saying the III version is made for both versions of the 100-400L? When I read up on the version II lens, there was an indication that it was paired to the III version converter. When I read up on the earlier lens, I thought I saw where the II version converter was recommended............confused here. It may work with either. Could be the III works better but was not available when the initial lens was made??? If I do purchase a lens, I also want the best converter available for it. Converters, while not cheap are not nearly as expensive as lenses as you know. Any possible clarification is appreciated and thanks! Tom