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08/01/2006 07:59:10 PM · #1 |
my mom just got me some extension tubes, but i have no idea what they do. Can someone help me out here?
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08/01/2006 08:16:25 PM · #2 |
| Extension tubes are generally for macro photography. They can also be used on telephoto lenses to allow them to focus closer. This is especially useful for photographing smaller birds or mammals. They fit between your lens and camera body and allow your lens to focus closer than it otherwise could. You will lose some light, making your lens effectively slower, but it has no affect on image quality. Depending on the tubes and the speed of the lens attached you may or may not have AF, or metering functions. |
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08/01/2006 08:30:10 PM · #3 |
First let's talk about old-fashioned lenses. When you focused one of these lenses, you moved it in or out--closer to the film or digital sensor or further away. When you move the lens out (away from the film/sensor) it focuses on closer objects. Each lens is limited in how far out it will go--you can't move it out further to focus on something really close.
Enter the extension tubes. They go between the camera body and the lens. They move the lens further away from the film/sensor so you can now focus on something much closer. A typical lens might not be able to focus on something closer than four feet away. With an extension tube, the same lens might be able to focus on something four inches away.
Many modern zoom lens have internal focusing mechanisms so they don't seem to be moving in and out as you focus. But extension tubes have the same effect; they allow you to focus much closer. Now you will be able to take pictures of bugs and other creepy-crawly things.
--DanW
edit to add: I see that someone else has answered with a good explanation.
Message edited by author 2006-08-01 20:32:05. |
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08/01/2006 08:36:10 PM · #4 |
| Excellent! I soooo envy you. Go give your Mom a hug. She did you a big favor. Have fun with your extension tubes. |
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08/01/2006 10:07:51 PM · #5 |
Originally posted by EricMGB1974:
You will lose some light, making your lens effectively slower, but it has no affect on image quality. Depending on the tubes and the speed of the lens attached you may or may not have AF, or metering functions. |
This is not really true. The amount of light loss from extension tubes is insignificant actually. The AF and metering all work fine also. I have never had any trouble and I have stacked 3 tubes on occasion...
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08/01/2006 10:10:53 PM · #6 |
i just tried using it with my kit lens 28-55, and it wouldent focus on anything :(
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08/01/2006 10:27:00 PM · #7 |
You'll probably need to be within a few inches (at most) under bright light to focus. Try moving closer without touching the lens until you achieve focus to get an idea of the range.
Message edited by author 2006-08-01 22:27:21. |
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08/01/2006 10:27:23 PM · #8 |
Originally posted by jmsetzler:
Originally posted by EricMGB1974:
You will lose some light, making your lens effectively slower, but it has no affect on image quality. Depending on the tubes and the speed of the lens attached you may or may not have AF, or metering functions. |
This is not really true. The amount of light loss from extension tubes is insignificant actually. The AF and metering all work fine also. I have never had any trouble and I have stacked 3 tubes on occasion... |
I have a Canon camera, Canon lenses, and Canon extension tubes. The extension tubes have the electrical contacts necessary for autofocus to work and I have not had any troubles with focus. But it is possible that the contacts don't work with some lenses. It is also possible that the autofocus mechanism in some lenses can't cope with the short distances. If autofocus does not work, you may need to focus manually.
The extension tubes don't have any glass in them, unlike a filter or tele-extender, so there is nothing to reduce the light. But there is an effect that changes the exposure. As the lens is moved forward, the same amount of light is spread in a larger area and thus the apparent brightness is less. You don't have to worry about this; your light meter reads the light falling on the sensor so it compensates for this effect. Film photographers who use extention tubes with external light meters need to compensate for this by mathematically computing the reduction in light.
--DanW |
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08/01/2006 10:34:02 PM · #9 |
Originally posted by jusdino4it:
i just tried using it with my kit lens 28-55, and it wouldent focus on anything :( |
Set your lens to 55, focus on infinity, and then point your lens at something really close--like an inch away. Back up slowly and see if something comes into focus.
One of my lenses won't focus on anything when set to wide angle. It seems that the point that is in focus is inside the lens!
--DanW |
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