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I'm looking for a macro lens. I have 28-105mm Nikkor which gives me "1:2 Magnification Ratio" (whatever that means). I found another lens, Tamron 90mm Macro, which has magnification ratio of 1:1.

Would the Tamron 90mm give me a more close-up shot than my Nikkor? I guess I don't understand what the 1:1 or 1:2 numbers mean.

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...Or this one, which is exactly the same question in disguise and (therefore) contains the answer: photo.stackexchange.com/q/6026 –  whuber Jun 14 '11 at 18:19
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1 Answer

1:2 means the image projected on sensor (or film) is up to half the size of real subject; 1:1 means it's up to exactly the same size as the real subject. So yes, 1:1 means you can take a more close-up shot. The ratio in technical specifications means the maximum magnification, you can magnify less by focusing from further away (or zooming out, if the lens is a zoom).

Approximate minimum size of subject that you can fill a frame with (using minimal focusing distance for the lens, and longest focal length for a zoom lens):

  • magnification ratio 1:1 - 24 x 36 mm on full-frame, 16 x 24 mm on APS-C
  • magnification ratio 1:2 - 48 x 72 mm on full-frame, 32 x 48 mm on APS-C

You can get even higher magnification by adding bellows or extension tube(s) between your camera and lens.

A serious macro shooter may want to consider a Canon system, because they have the MP-E65 lens with insane 5:1 ratio - subject is magnified 5 times compared to its real-life size.

The greater the magnification ratio you use, the thinner will be your depth of field.

As @jrista commented, many people consider only 1:1 or higher magnification lenses to be true macro lenses, while marketers will happily stick "macro" on any lens that will focus closer than lenses of similar focal length usually do.

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It should probably also be noted that "true" macro requires at least 1:1 magnification. A lens with 1:2 magnification can take close-up shots, but they are not truly macro shots, in which the scene is projected life-size onto the sensor. –  jrista Jun 14 '11 at 16:35
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@jrista I doubt there is any "official" definition of "macro", but yes, such line is drawn quite often; added a note on that. –  Imre Jun 14 '11 at 16:59
    
@jrista - I second @Imre on that. A 1:1.1 is just as a macro as 1:1. –  ysap Jun 14 '11 at 18:23
    
The definition of a macro lens is one that produces a life-size or larger image on the sensor (or film), with a minimum of 1:1 projection. As such, 1:1.1 would NOT qualify, although it would qualify as a close-up lens. The term macroscopic refers to things that can be seen by the naked eye...or "life size" elements of the world, vs. microscopic or smaller than life size. Ref: bing.com/Dictionary/… –  jrista Jun 14 '11 at 20:01
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The reason I tend to be a stickler on the point is that to a new buyer who gets into a discussion with an experienced macro photographer an hears that "macro" means "life size", then goes out and buys one of the third-party "macro" lenses that only focus to 1:2, are kind of getting shafted. Nikon and Canon are pretty clear that their macro lenses are full 1:1 magnification, but other manufacturers are sketchy on the point, and they use the term as a marketing ploy rather than as a proper description of the lens. I think new buyers should, ad the very least, be ware. –  jrista Jun 14 '11 at 21:58
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