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I have a Nikon 105mm macro VR lens and I am quite happy with it. This is a true macro and gives me 1:1 magnification. If I put an extension tube with this macro lens, will the image magnification increase? I am asking this question because most of the manuals of extension tubes details only for 50mm lens.

Thanks, NN

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It's worth noting that the 105 VR will accept teleconverters, which will also let you increase magnification. –  Dan Wolfgang Feb 27 at 13:22

1 Answer 1

up vote 2 down vote accepted

Well, the principle of extension tubes it to shift the focussing distance range closer : just for the sake of example, instead of say [1m, infinity] you'd get [0.5m, 5m] (because you're shifting the focal plane of your lens farther away of the imaging plane - sensor or film -, but I won't dwell on the optics/maths | EDIT : actually already available here on Photo.SE).

So you can put your lens closer than its "normal" minimum focussing distance, therefore you'll get a higher than 1:1 magnification.

However, there are some points to note (possible issues... or not ?) :

  • depending on the length of the tube you'll lose some light in the process, around 1 stop for ~12mm, 2 stops for ~20mm.
  • the depth of field is reduced also, because you're closer to your subject (if at the same aperture), getting your subject in focus might become tricky (without specific/heavy/inconvenient gear)
  • the gain of minimum focussing distance effect decreases as the focal length increases (less "efficient" on 100mm than on say 50mm)
  • you risk blurring because of camera movement (even very small movement at high magnification ratio, even on a tripod)
  • you risk squishing your subject (if it's an insect) because the distance between your front lens and subject becomes smaller (and see Nick Miners's comment below)
  • on a low quality (low price) tube you may lose AF (although it doesn't really matter for macro...), aperture because the lens contacts are not passed through
  • although no additional glass is involved, using the lens to focus closer than it was intended can degrade iamge quality
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Although the front element on the Nikon lens doesn't extend, it should be noted that on some macro lenses (e.g. those from Sigma) the lens gets considerably longer when close-focusing, so adding an extension tube may push the front element out further than the focusing distance. Something to be aware of. –  Nick Miners Feb 27 at 8:50
    
@NickMiners I have never seen this issue, but that's an excellent point ! –  FredP Feb 27 at 8:57

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