EF 12 II Extension tube vs. EF 25 Extension tube

You will lose AF using a 1.4x on a 100-400 IS on a Rebel XT. If you tape the pins then you can get the camera to attempt to AF. This is unlikely to be very acceptable (similar tricks lead to disappointing behaviour on my 20D and that has better AF than a Rebel XT) but might work if you have a lot of light and a high contrast subject.

Without knowing what you want the extension tube for I can't say which is better. The EF25II is longer than the EF12II. Both feature new digitally optimized air ;) Actually the only difference with the original versions is that the new versions let you mount EF-S lenses. I use a set of three Kenko tubes and they work fine for me with light lenses but will not mount EF-S lenses.

AF quits on most Canon bodies if the camera detects that the maximum aperture is slower than 5.6. The net result is using a 1.4x on any lens slower than f4 you will lose AF. Certain high end bodies will AF at f8 using the centre sensor.

Autofocus is useless for macro work, unless you're one of those bug hunters with the 180mm lens and a ring flash. Get the extension tube you need for the magnification you require. Since it's hard to know in advance what magnification you will require, it's best to have both tubes.

Autofocus is useless for macro work, unless you're one of those bug hunters with the 180mm lens and a ring flash.

Oddly, I find AF quite useful with a 100 mm macro lens, in quite a few situations other than insect photography (although it is often useful for that, too).

In case you didn't know, extension tubes are also stackable, meaning you'll be able to focus even closer still, meaning even greater magnification. So if the 12 doesn't cut it for you, get the 25 in addition to it, and then you can choose between 12mm, 25mm, and 37mm of extension. For what it's worth, I have 2 25's and a 12 that I use in various combinations.

Oh, and I think it's Kenko that puts out a set of tubes of various sizes that I believe were a lot cheaper than Canon's. While I ended up with the Canon's before I found out about the Kenko's way back when, extension tubes are probably the only accessory I'd have no qualms about using a 3rd party vs a genuine Canon.

Unless you are only planning to use the tube with very shot lenses you will want both. I have two 25mm and one 12mm, I might use them in any combination or all together, there is no problem with this despite Canon not recommneding it.

You can calculate the magnifiction the tubes will give with the lens focussed at infinity as M=E/F, where E is the total of the tubes length and F is the lens focal length. The magnification will increase further when the lens is focussed closer but this is tricky to calculate with moder internal focus lenses.

The 100mm macro gives about 2.2:1 with the stack of three tubes and set to clossest focus.

If you won't ever need to mount them to an EF-S lens, the Pro-Optic set of 3 EOS mount extension tubes can't be beat for value. Cheap price, but unlike some cheapies they have full electronic coupling plus they're nice and solid too.

Hi,

Extension tubes in various lengths are very handy to have in your camera bag. They will improve the close focus of a long lens, or make for macro capabilities when used on many "non-macro" lenses. I always have a set with me and have used them on many different lenses and cameras over the years.

For my Canon system, I currently have two 25mm, three 12mm and a Kenko set with 12, 20 and 36mm in it (these are approx. lengths, without actually going and looking ;-). Singly or in combination these give a lot of options.

Basically, the longer the lens' focal length, the more tube length you will need to get into true macro territory (say 1:2 or greater magnification, which is 1/2 life-size) if that's your goal. But, to some degree this depends upon the lens and the camera being used. For example, some lenses already focus quite closely, or some D-SLRs have effective magnification built into them (1.6X lens factor on Rebel/10D/20D/30D etc.) And, you can use the tubes in combination with the 1.4X extender to get even greater magnification.

When an extension tube is installed on a lens it will no longer focus to infinity. This is okay, since the whole point is close-focus or macro. Nice thing about extension tubes is that they have no optical elements. Adding optics to the front or rear of any lens will nearly always degrade the image in some respects, a little or a lot depending upon the quality of the optics and how well they are matched to the lens being used. Extension tubes leave the lens' optical formula intact and simply can't cause these sorts of problems.

To give you some ideas, I've used 12mm on an EF 20/2.8 and had flower petals in focus while they were actually touching the front element of that lens. A 50/1.4 becomes a neat close-focus or macro lens with 12 to 25mm of extension. EF 85/1.8 also works well with 25 or more mm of extension. (Another approximationi is that to get to 1:1, or life size, you need total extension equal to the focal length of the lens. I.e., use 50mm of extension on a normal 50mm lens. However, again, it depends upon the actual lens & camera in use.)

It's been pretty well addressed already. But, the 1.4X Extender "costs" you one stop of light, which is lost when light is passing through that lens' optics. When installed on lenses that are already only around f5.6, your camera will have trouble AFing with the 1.4X installed and only effective f8, thus the hunting. Plus, the 1.4X can only be installed and is designed to work with longer lenses. In your kit, likely only the 100-400, but it sounds like that's the lens you want to use it on. Be prepared to manually focus the lens when racked out to 400mm with the 1.4X installed. (I hope you have it on a tripod, too, even with I.S., since this is the equivalent of nearly 900mm telephoto on a full-frame camera! 400mm x 1.4 x 1.6 = 896.)

Note, there is some light fall-off when using extensions, too. So, a tall stack of them might cause similar difficulty with AF. However, a lot of folks don't use AF with macro photography, anyway. I.S. is likely to be less than effective when very close-up, too.

Stacking a bunch of extension tubes together will likely slow AF and/or I.S. due to all the extra electrical connections being made. The tiny trickle of power passing between lens and camera body has to cross those connections. The more connections there are, the less efficient it is, so communication and power functions slow down.

Canon's tubes are very well made, mostly metal and I think the electronic contacts are gold plated. Kenko's seem fine, too, but are polycarbonate bodies, and probably not gold plated contacts (Hey, they gotta save $ somewhere, to sell them so much cheaper). Besides the 3-tube set offered (which is a sort of traditional way these tubes have been offered) Kenko also makes 12mm and 25mm individual tubes, which might be higher quality in some ways, aren't much cheaper than the Canon tubes.

You can get into all kinds of math and calculations of magnifications with various combos of tubes and lenses. However, I just suggest experimenting and learning what to expect with a few key combos. This might be more practical out in the field.

If it's an area of high interest to you, there are some really good books out there about using many methods to shoot macro or near-macro close-ups. If I recall, Tim Fitzharris has written one or two specifically about the subject. John Shaw's "Close-Ups in Nature" is excellent. And George Lepp's "Beyond the Basics" gets into the subject in some detail.

Cheers!

Alan

Danny, if I were you I would just return the Canon extension tube and get the Kenko extension tube set. For the same price as the Canon, you get 12, 20, and 36mm Kenko tubes in the set. These tubes don't have glass like the Canon tubes. Therefore, you won't be compromising IQ by going third party. Are you intending to use the extension tube w/ your 100-400 IS to do some macro photography?

As far as putting tape on the TC, I used regular scotch tape, and it worked fine. Again...AF will work, but it will hunt...meaning it will have a hard time focusing...and it's possible it may not find the correct focus at all.