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Why is 1:1 desirable for a macro lens? I know it means that you can print a picture of something and it will be the same size on paper as it is in real life, but why is this such a desirable feature over, say, a lens that magnifies even more?

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In addition to the magnification (1:1), the focal length is important. 50mm and 65mm lenses are fine for still-lifes, but if you try sticking that lens next to a creature you're likely to see it leave quickly. My favorite length is Nikor's 105mm "micro". It's not a super-fast focusing lens, but it lets you stay a foot away, which gives you a fighting chance to get butterflies and spiders. If you're after more skittish things, then you'll probably want something with even longer reach, like a 200mm. That's especially important if you're after dangerous things like rattlesnakes. –  Greg Jan 31 '11 at 21:57
    
I love my Canon 100 Macro: It allows multiple settings for .3-.5 M, .5-infinity, and Full. It is a 2.8, and if you don't mind the price, it is a wonderful lens for various macros ! –  Clinton S. Boze Jun 28 '11 at 13:14

3 Answers 3

up vote 19 down vote accepted

You're close on what 1:1 means but slightly off. A 1:1 macro lens means that the size of the subject is projected onto the sensor (or film) at the exact same size it is in real life. You can blow up the print as large as you like :)

The ability to go to 1:1 is just a metric and there are a lot of compromises that come with being able to enlarge a subject to 1:1 the most obvious one being focusing speed since there is a larger range (distance) over which the lens can focus. There are lenses that go even closer, the MP-E 65 goes from 1:1 to 5:1 magnification, its a manual focus only lens though :)

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The biggest compromise new macro users notice is normally the limited depth of field. The larger the magnification the less depth of field you get. So while you might be tempted to grab the MP-E 65 because of the 5:1 number, it's a very specialised lens. Great for flat subjects :) –  Мסž Jan 31 '11 at 22:46
    
Yea, there are a lot of complications with macro photography in general and the closer you get to the subject the more those issues are an issue :) –  Shizam Jan 31 '11 at 23:12
    
Thanks for the great answer, Shizam. –  Daniel T. Feb 1 '11 at 8:36
    
Actualy, the MP-E 65 isn't a manual focus lens, it's a fixed-focus lens. The mechanism you adjust is a zoom. The zoom operates "backwards"; that is, the distance between the film plane (sensor) and the lens node is fixed, and when you change the focal length of the lens what would normally be the backplane of the optics (which is now pointed at the subject) changes very little while what would have been in front in a normal design changes quite a bit. You change the size of the image on the sensor by zooming; focus is almost entirely by camera position (which is critical). –  user2719 Feb 1 '11 at 14:06
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Doh, Stan is right. Its manual focus like a prime lens is manual zoom, you gotta move it :) –  Shizam Feb 2 '11 at 17:35

The 1:1 designation means that the image of a subject projected onto the sensor (or film) is the same size on the sensor as real life, and is the minimum magnification to classify as true macro. There are lenses that do magnify more, such as Canon's MP-E 65 which can magnify images between 1 and 5 times their real-world size.

The benefit of 1:1 magnification is that you can truly enlarge and enhance real-world detail in print. This is in contrast with normal lenses, which often only magnify 0.15x, or 1:6. A print would need to be enlarged six times to present the same amount of detail as a 1:1 lens...assuming you could resolve that amount of detail in the first place.

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It's amazing the first time you do an enlargement from a 1:1 macro shot and see the detail the lens and sensor are capable of catching. –  Greg Jan 31 '11 at 21:52
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This answer doesn't address the question. What is so special about 1:1? Is it a special milestone? If so, why? If not, do people treat it as one? –  Oddthinking Jan 31 '11 at 22:06
    
@Oddthinking Not sure what you mean there -- the 1:1 is the classification of true macro, as it says in the answer... –  Rowland Shaw Feb 1 '11 at 7:52
    
Sure, but why is "true macro" so special? Imagine 1:0.9 or a 1:1.1 lenses. Both could "truly enlarge and enhance real world detail in print". 1:1 = True Macro seems to be an arbitrary metric, and not intrinsically any more desirable than nearby and/or even more powerful magnifications. –  Oddthinking Feb 1 '11 at 11:58
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@Oddthinking You have to draw a line in the sand somewhere - 1:1 is verifiable in the days of film (overlay the real object on the film - if it's the same size or larger on film, then it's a true macro), any other figure would involve measuring, and calculating. –  Rowland Shaw Feb 1 '11 at 12:49

There is nothing specifically desirable in a 1:1 magnification for macro. This is just a convention, where, as pointed out in Rowland's answer, to designate a "true" macro lens.

This does not mean that a lens with 1:0.9 max magnification cannot do a good macro work (if you can find such lens). I guess it depends on what exactly is it that you want to shoot. Depending on your subject's size, relative to the sensor's size, you can choose lenses with different max magnification.

Generally speaking, for insects, a 1:1 is a good bet. For insect eyes or sugar grains (...) an MP-E 65 may be better. For flowers, OTOH, a non-"real" macro lens can do decent work as well.

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65mm is seriously pushing it for insect eyes because you'd be right on top of them. Insects I tried shooting with a 105mm were nervous because I was too close. Maybe chilling them so they are sluggish would allow the 65mm, but for field work I think something longer is needed. –  Greg Jan 31 '11 at 22:00
    
Don't let the 65mm f/2.8 specification of the MP-E fool you. Both are measured at infinity. The lens cannot actually focus at infinity. It cannot focus at anything like infinity, so both numbers are actually rather meaningless for practical purposes. At 5:1 magnification it accordions to almost nine inches in length. It is not your typical 65mm setup! –  Staale S Jan 31 '11 at 23:36
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@reg - LOL, my only experience with shooting bug eyes are eyes of a dead fly... –  ysap Jan 31 '11 at 23:44
    
@Greg: I would dispute the fact that insects get nervous with the MP-E 65mm. I know several photographers on DeviantArt.com and 1x.com who use the MP-E 65mm to GREAT effect with insect portraits, some of them right up to 5x magnification. Of all the lenses used by insect macro photographers, Canon's MP-E seems to be the king for those truly fantastic extreme-magnification shots. It just takes the right technique and skill to use it without scaring off every insect you go to photograph (i.e. using honey to bait bees and keep em around for a while while you photograph them.) –  jrista Jun 28 '11 at 15:51
    
@jrista, From personal experience, not based on what others have done, in the field trying to work with butterflies and spiders, a 105mm has a lot better chance of success than 65mm. You can't get on top of a butterfly, except in the early hours when they're cold because they are skittish. All the photos I've taken of them were from several feet away and took a lot of patience and very slow movement. Flies, beetles and other insects might be happy to cooperate with a 65mm lens next to them but active flying ones don't like it. –  Greg Jun 28 '11 at 17:13

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