what are the disadvantages for using an extension tube?
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kelster said:
I believe he is refering to an extension tube for macro work, not a teleconverter.
Depends on what your requirements are. If u want to shoot macro but don't want to buy a specialised macro lens, an extension tube is a good budget choice. Your working distance is very short however, and characteristics vary depending on the lens you are using with.
no, you wont loose stop. The extension tube is just pulling your focus distance closer to your object. BUt use it with tc can have different magnification depending on how you combine them.
Another way to take macro pic is by coupling two lens, it will definitely look different. But beware of the glasses contact distance with your object! And dont let the ratio of the coupling lens be too large because you might having situation the object touching your lens' glass.
Another way to take macro pic is by coupling two lens, it will definitely look different. But beware of the glasses contact distance with your object! And dont let the ratio of the coupling lens be too large because you might having situation the object touching your lens' glass.
finkster said:
The purpose of having extension tube is to reduce minimum focusing distance. For example if you can only focus at 2 meters with a 300mm lens, with extension tube you will be able to focus at a shorter distance, probably 1 meter or 1.5 meter depanding on which tube you are using.
Ok guys, back to my question : what are the disadvantages for using extension tube?
shorty said:
Yes. There's some light lost when using extension tubes.
50mm extension tube can decrease your exposure by one full stop. The longer the extension tube length, the greater the light lost. But you dont have to worry about this, the built in TTL metering of you cam can recognise the presence of extension tube and adjust the meter reading accordingly.
The best part is that, you'll not degrade the image quality.
From http://www.web-nat.com/bic/ont/tips41.html
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There are a few disadvantages of using extension tubes. First, the addition of the tube does reduce the amount of light reaching the film, so like teleconverters; they do cost you some light. The amount of light lost however, is much less than when using TC's. The amount can be approximated by the following formula. Extension tube length / focal length of the lens used. Therefore 25 mm of extension divided by a 400mm focal length lens gives 1/16 of an f-stop of light loss.............relatively insignificant compared to a full stop lost with a 1.4x TC.
The second disadvantage concerns electronic coupling of the light meter and autofocus systems with the extension tubes. Depending upon your camera manufacturer, you may lose some light metering modes such as matrix/multi-segment metering. The autofocus capability may also be lost.
Another disadvantage of the tubes concerns the magnification itself and the mechanical connection of the tubes. Since the magnification has been increased, any vibrations will also be magnified necessitating the need for good technique and higher shutter speeds. Aggravating this vibration problem is the mechanical coupling of another device. There is always some "play" or looseness when a camera and lens are mounted together. The addition of an extension tube adds two more connections to create instability/movement to the system. The end result is increased vibration and blurry photographs.
The last disadvantage of using extension tubes is that you lose the ability to focus at infinity. The lens is limited to a much smaller zone that it can be focused upon. For bird photography this is not really an issue since a bird 50 feet away will be too small in the frame to photograph anyway. How far away the lens will focus with a given extension tube is related to the focal length of the lens. The shorter the focal length of the lens, the greater the loss of the lens's far focusing ability.
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************* START OF QUOTE *************
There are a few disadvantages of using extension tubes. First, the addition of the tube does reduce the amount of light reaching the film, so like teleconverters; they do cost you some light. The amount of light lost however, is much less than when using TC's. The amount can be approximated by the following formula. Extension tube length / focal length of the lens used. Therefore 25 mm of extension divided by a 400mm focal length lens gives 1/16 of an f-stop of light loss.............relatively insignificant compared to a full stop lost with a 1.4x TC.
The second disadvantage concerns electronic coupling of the light meter and autofocus systems with the extension tubes. Depending upon your camera manufacturer, you may lose some light metering modes such as matrix/multi-segment metering. The autofocus capability may also be lost.
Another disadvantage of the tubes concerns the magnification itself and the mechanical connection of the tubes. Since the magnification has been increased, any vibrations will also be magnified necessitating the need for good technique and higher shutter speeds. Aggravating this vibration problem is the mechanical coupling of another device. There is always some "play" or looseness when a camera and lens are mounted together. The addition of an extension tube adds two more connections to create instability/movement to the system. The end result is increased vibration and blurry photographs.
The last disadvantage of using extension tubes is that you lose the ability to focus at infinity. The lens is limited to a much smaller zone that it can be focused upon. For bird photography this is not really an issue since a bird 50 feet away will be too small in the frame to photograph anyway. How far away the lens will focus with a given extension tube is related to the focal length of the lens. The shorter the focal length of the lens, the greater the loss of the lens's far focusing ability.
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