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I own this (mechanically and optically superb) lens since quite some time and was wondering why the blue marks that say 1:1, 1:1.5 and 1:2 don't actually correspond to the reproduction ratio that the lens produces on my full frame sensor.

enter image description here Photo courtesy of Erik Haak / Chasa Imago / Flickr - https://www.flickr.com/photos/chasa-imago/

Here are (resized) jpegs from untouched raw files from my Nikon D750 showing a metric ruler at about the closest focusing distance (shot at f/11).

I get to 1:2, not 1:1.

enter image description here

I can get to 1:1, but only by adding the PK-3 extension ring:

enter image description here

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After doing some more research, I found out that indeed the markings tell the reproduction ratio that can be achieved when an extension ring is mounted along with the lens.

From the lens manual:

M2 Ring distance and reproduction ratio scales - For focusing when M2 Ring is used

Source: Micro Nikkor 55 Manual (page 2 and 3)

There were several versions of the extension ring for Nikon F mount:

  • M - from 1963 to 1968
  • M2 - from 1969 to 1973
  • PK-3 - from 1976 to ?
  • PK-13 - from 1977 to 1979

Source: Accessories Close-up Extension RIngs

They all provide 27.5mm extension and allow to reach 1:1 reproduction ratio.

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These are marks which tell you what magnification ratio you will get when focusing on object on this distance. For example 1:1 mean you will have the same size projection of object to the film or sensor. 1:2 means projection would be half the linear size of the object.

Based on the comments you can reach 1:1

if coupled with the PK-3 or PK-13 extension rings

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  • \$\begingroup\$ That is what I thought too in the first place but this lens does not produce a 1:1 (lifesize) image on a FF sensor (Nikon D750 in my case). Only 1:2 at the closest focusing distance. \$\endgroup\$
    – MrUpsidown
    Sep 1, 2022 at 13:00
  • \$\begingroup\$ @MrUpsidown, this is odd, usually these signs are quite precise and the lens is for FF sensor. \$\endgroup\$ Sep 1, 2022 at 13:08
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    \$\begingroup\$ I found from various sources that this lens can achieve 1:2 and 1:1 if coupled with the PK-3 or PK-13 extension rings. I also tested it by taking a picture of a ruler at minimum focusing distance and I get about 70mm in the frame. \$\endgroup\$
    – MrUpsidown
    Sep 1, 2022 at 13:25
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The blue markings indicate the reproduction ratio that will be yielded by the lens when used in combination with Nikon's PK-3 or PK-13 extension rings.

Both of these extension rings add 27.5mm to the distance from the lens flange to the camera's flange ring. The additional distance between the lens and the camera allow closer Minimum Focus Distance, which increases the reproduction ratio compared to using the lens attached directly to the camera.

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  • \$\begingroup\$ OK, but isn't that a bit weird? I am surprised the lens itself would read 1:1 when it can only reach 1:1 with an extension ring. Or is this common practice? \$\endgroup\$
    – MrUpsidown
    Sep 1, 2022 at 18:21
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    \$\begingroup\$ @MrUpsidown I don’t know how common it is, but I can tell you that the Canon EF 50mm f/2.5 Macro also has 1:1, 1:1.2, 1:1.5, 1:2, and 1:4 markings on the barrel even though it is only 1:2 max magnification on it’s own. Canon has a matching “Life-Size Converter” which has a 4-element optical element and acts like a teleconverter to bring it up to 1:1 Macro. \$\endgroup\$ Sep 1, 2022 at 20:53
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    \$\begingroup\$ My 55mm macro came new with the M2 extension which gives 1:1 (and it operates the aperture opening tab). Guessing you may have bought yours used, missing the ring. It is a 27.5 mm extension ring. Ebay might have one. \$\endgroup\$
    – WayneF
    Sep 2, 2022 at 15:34
  • \$\begingroup\$ @MrUpsidown It seems to have been more common in the manual focus era with 1:2 lenses often bundled with extension rings or other attachments that gave them 1:1 reproduction ratios at the expense of infinity focus. Once Autofocus got going at the end of the 1980s, attachments that required manually focusing an AF lens got much less popular very quickly. \$\endgroup\$
    – Michael C
    Sep 2, 2022 at 20:08

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