So I bought a Kiron 105mm f2.8 1:1 lens recently to be used with my Sony a6000. I know that the difference between a 50mm macro and a 100mm macro is how close you can get to your subject, that is with 100mm you can back up a little bit and still get the same magnification.

But when I tried getting some pics with my Kiron lens at 1:1 setting I still have to get pretty close to the subject (probably about 15cm or so from the front end of the lens) to get it in focus. Although I have heard people say 100mm macro is good for insect/bug photography as you can get pics without scaring them off, my working distance is still pretty small at 1:1, which probably isn't a practical distance.

Can someone explain what I'm not getting here? At 1:1 magnification ratio is there a real difference in using a 50mm or a 100mm in terms of the working distance?

  • A 15cm working distance for a 100mm macro lens is about standard. 50mm is usually about 10cm. – ElendilTheTall Jul 20 '15 at 9:35
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    so it's all for the 5cm difference..? – samsamara Jul 21 '15 at 1:59

When a macro lens has a reproduction ratio of 1:1 an object with a given size will be reproduced at the image plane at the same size. This is irrespective of the focal length. The only difference is that a longer focal length will afford you the ability to achieve that reproduction ratio at a greater distance than the shorter focal length.

The precise working distance (distance from the front of the lens to the subject) is dependent on more than just the focal length. The specifics of the optics used in a particular lens will dictate the working distance. Focal length is the distance from the rear nodal point of the lens to the image sensor. The location of the nodal points shift depending on the optical formula and can in some cases be in front on the front element or behind the rear element. Generally, however, a shorter lens of a particular focal length will have a greater working distance than a longer one at the same reproduction ratio.

  • i think your answer makes sense. So if my Kiron lens was not extending physically when I'm going for the 1:1 (which it does now) i would be getting more working space. I see in this case, it's a limitation of the lens design right? – samsamara Jul 21 '15 at 5:22
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    I'm not familiar with that particular macro, but the lens design will impact the working distance. I'm not sure how the working distance of Kiron compares to other brands but I wouldn't expect it to be incredibly different. – agf1997 Jul 21 '15 at 5:25

As agf1997 says, minimum focus distance for macro lenses varies somewhat with lens design, however as a rule of thumb you can expect the minimum focus distance (i.e. minimum working distance) to be roughly the same as the focal length of the lens (assuming 1:1 magnification here). Hence a 300mm lens with a whole lot of extension tubes (as a silly example to illustrate the point) should give you 1:1 magnification and a working distance of about 300mm from your subject, compared with approx. 50mm working distance for a 50mm macro lens at 1:1 magnification. In my experience, longer macro lenses are much more useful for most subjects unless you are copying flat smallish documents on a copy stand that will only accommodate a shorter focal length. Another practical example is one of perspective; if you fill the frame with a person's face using a 50mm lens, the resulting 'peephole' perspective is quite distorted (because the subject>focal plane distance is short), whereas framing the face the same way with a 105mm lens will give the face a much more realistic appearance. This example isn't quite macro photography per se, but the concept applies equally.

  • The perspective and depth of field will be identical regardless of focal length at a particular aperture at 1:1 though the distortion may be different. – agf1997 Jul 21 '15 at 17:49
  • By perspective I mean 'viewpoint', which is obviously closer at 1:1 with shorter focal lengths. This is especially important in scientific photography. – HamishKL Jul 21 '15 at 22:03
  • I'm not following what you mean by "viewpoint". Can you explain? – agf1997 Jul 21 '15 at 22:38
  • @agf1997: I mean the point in space relative to the subject from which the camera views the subject. – HamishKL Jul 21 '15 at 22:48
  • A couple of problems with this answer: MFD is measured from subject to the sensor plane. Working distance is measured from the subject to the front of the lens. Working distance will always be the flange focal distance+lens length shorter than MFD. Also, extension tubes aren't very effective for long lenses. By the time you add enough extension tubes to give a typical 300mm lens a 1:1 reproduction ratio, the focus distance needed is shorter than the lens (i.e. inside the lens). – Michael C Oct 13 '15 at 2:33

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