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Extension Tubes


timtom1 e2
10 26
14 Jul 2004 5:17PM
I have the Jessop's extension tubes which are 13mm, 21mm and 31mm, I have been using them with a 28 x 100mm Nikkor Lens and a 70 x 300mm lens I find that I have to get about 5cm away from my subject before it comes into focus.

Can I with these extension tubes and another lens say a 50mm lens get close up photo's of a deer for example from a distance?

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tim franklin e2
11 2.7k
14 Jul 2004 5:21PM
No. Wouldn't that be nice though!

Extension tubes reduce (as you have found) the minimum focusing distance, and hence increase the magnification of a given lens. What you lose however is infinity focus....and indeed all focus betwen infinity and the new extension-enhanced minimum.
Chris_H e2
11 1.5k 1
14 Jul 2004 6:24PM
It sounds like you are after a 1.4 or 2x converter which will if using a 2x converter double the focal length of your lens so 300mm becomes 600mm
spaceman e2
10 5.2k 3 Wales
14 Jul 2004 8:01PM
Careful though Tim - tele-converters also reduce the maximum aperture of the lens. If your 300mm has a maximum aperture of F5.6 a 2X converter would turn it into a 600mm F11. Very small.
timtom1 e2
10 26
14 Jul 2004 9:04PM
ok thanks
zippie e2
11 1.3k England
14 Jul 2004 11:49PM
Wouldn't it turn it into an f8 not an f11 ?
Pete e2
13 18.7k 96 England
15 Jul 2004 7:03AM
no, it is two stops as Michael (spaceman)says.
nikon5700ite 10 1.8k
15 Jul 2004 10:12AM
The aperture is found by dividing the focal length of the lens by the diameter of the iris while using inches [imperial]

So double the focal length and you four times the effective aperture. So f/5.6 becomes f/11 as said above.

I think to be pedantic you should describe your lens as f/2.8 100mm lens and f/7 300mm ... in which case the 300mm with a 2x converter would mean the aperture off around f/15 [without putting my thinking cap on to work it out exactly Smile] Rather restrictive but you pays your money through the nose if you want speed and focal length.
ejtumman e2
10 2.8k England
15 Jul 2004 11:27AM
Going back to extension tubes, do you have to increase the exposure at all with those?
kit-monster e2
11 3.7k 2 Singapore
15 Jul 2004 11:32AM
You do loose some light but only a little and no where near as much as with converters. Best 80 quid I spent on camera kit.
digicammad e2
11 22.0k 37 United Kingdom
15 Jul 2004 11:42AM
Yeh but Ed you only bought the extension tubes to make your lens even longer! lol

On teleconvertors. I bought myself a Raynox 1850pro, which is 1.8x. It has a massive glass area and I'm sure it doesn't cost me 2 stops, at least it doesn't feel that way when I use it.

Ian
Chris_H e2
11 1.5k 1
15 Jul 2004 3:51PM
if you get a 1.4x converter i Think you only lose 1 stop of light.
spaceman e2
10 5.2k 3 Wales
15 Jul 2004 5:22PM
Emma, extension tubes do reduce the amount of light coming through the lens but the camera meter will automatically make the necessary adjustments.
16 Jul 2004 12:06AM
80! Hehe! My Af tubes for NIkon cost me 6! It is important to note that with NIkon matrix metering the exposure will not be 100% accurate with extension tubes, unless they are Nikon ones. To matrix meter properly the camera needs to know how bright it is outside the camera. It can only work this out accurately if it knows the exact maximun effective aperture of the lens. Third party tubes don't convey the necessary info to the camera body.
lordposh e2
10 45 United Kingdom
16 Jul 2004 7:59AM
Gary thank for the advice can I offer you 6.50 for your tubes...!! LOL

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