Extension Tubes

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st599

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I've been offered the chance of tagging along on a safari camping trip.

I have a fairly OK 250mm telephoto zoom that can open up to f/5.6 but it sounds like 400 mm may be more appropriate.

Can you get a 2x extension tube like you can for video cameras? I've seen some but they are claiming to be for Macro work. Will these work? Will auto focus still work?

Thanks
 
You actually mean a 2x teleconvertor, not extension tubes
Teleconvertors do in effect increase the focal length but don't work well with all lenses and you lose f stops
 
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You don't actually mean extension tube as these are for making lenses focus closer; what you really mean is teleconverter. These are available in 1.4x and 2x but a 1.4x would make your f5.6 lens f8 and the 2x would make it f11. AF is very unlikely to work.

You can't start with a 'fairly OK' lens if you want to use a teleconverter; you have to start with 'good' at least or you're just wasting time and money.
 
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Extension tubes are for macro. To increase the focal length of your lens you need a converter. Canon make a 1.4 and a 2 times. Nikon make a 1.4, 1.7 & a 2 i think.

To find the focal length you multiply the focal length of your lens by the conversion factor. e.g 200mm with 1.4 = 280mm. This does not take into account any crop factor affecting the field of view.

Whether you can still AF with a convertor depends on the max aperture of your lens. With a 1.4 you will lose a stop of light so a 200mm f4 with a 1.4 attached will be a 280mm f5.6. Most cameras will still be able to AF at f5.6 but if you use a x2 converter and the aperture becomes f8 then you will need, with Canon, a 1 series body or a 5d MkIII with the latest firmware to be able to AF. I dont know which Nikon or other brand cameras can AF at f8.
 
st599 said:
I've been offered the chance of tagging along on a safari camping trip.

I have a fairly OK 250mm telephoto zoom that can open up to f/5.6 but it sounds like 400 mm may be more appropriate.

Can you get a 2x extension tube like you can for video cameras? I've seen some but they are claiming to be for Macro work. Will these work? Will auto focus still work?

Thanks
Click to expand...

You mention video cameras - did you have something like this in mind? http://www.raynox.co.jp/english/dcr/dcr2025pro/index.htm

This is not an extension tube or converter in the traditional sense, but might work for you. However all the comments about an 'OK' lens will still apply, and you may be better off trying to find a used 400-500mm lens.
 
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