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Old May 19, 2004, 3:47 PM   #1
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like EF12 II or EF25 II - what do they do? I'm buying myslef my first SLR (d70 or 300d) and I don't know what these extension tubes do? It seems to be such a trivial question that I can't find an explanation on the www. If it says it's going to add 0.5× - 0.9×magnification (I don't know exact numbers now) does this mean that 18-55mm lens become (1.6+0.5)×18mm - (1.6+0.9)×55mm?

What do you think about these extension tubes? Is it ok to use them?
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Old May 19, 2004, 4:23 PM   #2
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Extension tubes sit between the lens and the camera - pushing the lens further away from the film/sensor.

They're for macro work, they change the nearest-focus point and effitive magnificaton if you're taking pictures of ants or wasps. They're not for "everyday" use. I'm after a set - but I wouldn't suggest they'd be near the top of everybody's "must have" accessory list.

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Old May 19, 2004, 4:39 PM   #3
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Thanks, ccomley. So they're only for macro work. That's all I wanted to know.
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Old May 20, 2004, 9:30 AM   #4
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While I generally agree with what ccomley said, I wanted to add that it isn't exactly correct.

While you can use it to shoot wasps or ants (but there are better ways to do that), tubes are also useful for other things. The close focusing distance of my 100-400L is 1.6 meter (about 6 feet or so.) Anything close than that I can not focus on. Of I wanted to get a picture of a small frog or toad, I might not be able to get close enough to fill the frame with it (get any close & I can't focus!) An extension tube will allow me to get closer and still focus (but not focus at infinity.)

If I had one of the big prime lenses (500mm or 600mm) they have a minimum focusing distance of something like 15 or 20 feet. That is far away! With some birds, I can get much closer to them than that... but I wouldn't be able to focus on them. Extension tubes are the answer.

The way to view a tube is this (at this, this is how I do it.) When you use a specific lens, there is a region in space that the lens can focus. It start at some distance in front of you, and goes really far out (usually to infinity.) For some lenses the start of that region is really close (a macro lens, for example) and in others is really far away. The job of an extension tube is to bring that region you can focus in closer to you. That means the more extension tube you use (i.e. the further you move the lens away from the body) the closer you can focus, but the less you can focus further away.

If I ever buy a 600mm lens (really expensive) I will definitely buy a set of extension tubes.

Two other things to note. 1) There is nothing special about an extension tube. Don't get the Canon tubes, get the Kenko set. Much cheaper... and heck, probably exactly the same (i.e. Canon probably contracts with Kenko and rebrands them.) 2) You loose a little light the more extension tube you use. It's around 1/3 of a stop or so, but it's more with more tube. Metering will correct for this, but you'll loose a little shutter speed.

I hope that wasn't too much info and confused you. Feel free to ask a question if you need.

Eric
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Old May 20, 2004, 4:52 PM   #5
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I don't disagree with your more detailed version.

But I think Trdi was thinking that tubes might increase the effective focal length of his lens like a teleconverter, so I hope he's now clear that's not it at all.

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Old May 20, 2004, 10:38 PM   #6
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Well, by allowing you to get closer to the subject to take a picture it is kinda like magnifying them. But I guess that is a stretch.

Eric
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Old Jul 7, 2005, 4:51 PM   #7
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I'm thinking of getting the Canon Extension Tube EF 25 II to use with my 85mm 1.8 lens. Minimum focusing distance is 2.8ft. What would it be with this tube? Also, what does it mean on Canon's lens chart when they say that this combination would have a magnification of 0.44–0.32? Why a range rather than a single number?
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Old Jul 7, 2005, 8:29 PM   #8
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FYI - http://www.shutterfreaks.com/Tips/ExtensionTube.htm

I believe eric s got it right... the magnification varies with the distance of the object
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Old Jul 8, 2005, 6:09 PM   #9
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OK, I got it and I get it.:idea: With the 25mm extension tube, the 85mm can only focus within a very narrow range, described by the range of 0.44–0.32 magnification.
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