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Extension Tubes

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timtom1  1026 forum posts
14 Jul 2004 - 5:17 PM

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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14 Jul 2004 - 5:17 PM

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tim franklin
14 Jul 2004 - 5:21 PM

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  101472 forum posts1 Constructive Critique Points
14 Jul 2004 - 6:24 PM

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  105166 forum posts Wales3 Constructive Critique Points
14 Jul 2004 - 8:01 PM

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  1026 forum posts
14 Jul 2004 - 9:04 PM

ok thanks

zippie  101329 forum posts England
14 Jul 2004 - 11:49 PM

Wouldn't it turn it into an f8 not an f11 ?

Pete Site Moderator 1318443 forum postsPete vcard ePz Advertiser England96 Constructive Critique Points
15 Jul 2004 - 7:03 AM

no, it is two stops as Michael (spaceman)says.

15 Jul 2004 - 10:12 AM

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  102756 forum posts England
15 Jul 2004 - 11:27 AM

Going back to extension tubes, do you have to increase the exposure at all with those?

kit-monster e2 Member 113685 forum postskit-monster vcard Singapore2 Constructive Critique Points
15 Jul 2004 - 11:32 AM

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  1121988 forum posts United Kingdom37 Constructive Critique Points
15 Jul 2004 - 11:42 AM

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.


Chris_H  101472 forum posts1 Constructive Critique Points
15 Jul 2004 - 3:51 PM

if you get a 1.4x converter i Think you only lose 1 stop of light.

spaceman  105166 forum posts Wales3 Constructive Critique Points
15 Jul 2004 - 5:22 PM

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 - 12:06 AM

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  1045 forum posts United Kingdom
16 Jul 2004 - 7:59 AM

Gary thank for the advice can I offer you 6.50 for your tubes...!! LOL

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