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I've read a few threads on here that mention some elementary descriptions of macro lenses and found some marketing fluff in the box for my Canon about them as well, but being a complete novice I was left a bit confused.

Can someone please provide me with a top-to-bottom explanation of what a macro lens does?

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4 Answers 4

up vote 26 down vote accepted

True macro lens gives you a 1:1 magnification -- that is a ratio of size of the subject and its image on the sensor. With 1:1 magnification on APS-C sensor (22×15 mm), you can fill whole picture with area of this size.

Other properties of macro lenses include that they have fixed focal lengths, usually very low distortion (see distortion figures of Canon EF 100mm macro at photozone.de for example). Also, macro lenses tend to have non-rotating and non-moving front elements which is useful since you put them very close to the thing you're shooting.

Mostly due to marketing reasons, term macro is now used for lenses with 1:2 or even lower magnification. (Tamron AF28-200mm F/3.8-5.6 XR Di Aspherical (IF) Macro has 1:4, which means on APS-C body the smallest area you'll focus on is 88×60 mm.)

On compact cameras, macro means "setting where you can focus a bit closer". (Although, as Roddy points out, this can sometimes get you close to actual macro range: Panasonic TZ5 can capture a 63×47mm area, which gives results similar to lens with 1:3 magnification on APS-C DSLR -- image quality aside)

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4  
Good answer. One other point to add is real macro lenses tend to have flat-field focus, which means the plane of focus is parallel to the sensor. Other lenses have curved-fields, which make it more difficult to get what you want in focus, even in non-macro situations like photographing pictures. This is not the same as geometric distortion. This is also why some lenses have much lower edge-sharpness scores. –  Eruditass Aug 7 '10 at 21:06
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Capturing the same area with a smaller sensor doesn't get you the same (or even comparable) magnification. The results can certainly be similar, but dragging in magnification clouds the definition a little. –  ex-ms Aug 7 '10 at 21:32
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I don't think that having a fixed focal length is a defining property of a macro lens. They almost always happen to be, but one could in theory have a true macro zoom lens. –  mattdm Nov 26 '10 at 18:59
    
@mattdm: And are there any 1:1 macro zooms? –  che Nov 26 '10 at 20:51
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@khedron: The idea is to fill the entire picture frame with an in-focus subject of your sensor size (e.g. 22x15mm). That is 1:1 Macro. As for flat-field focus, it isn't assumed, nor explicitly stated all the time. Many zooms with the "MACRO" designation do not feature this. –  Eruditass Feb 17 '11 at 4:41

Che wrote...

On compact cameras, macro means "setting where you can focus a bit closer".

On some compacts, macro mode can be incredibly effective. My Panasonic TZ4 focuses down to a couple of inches. Mayflys are big, but not this big.

alt text

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Thanks for pointing this out, I added a bit to my answer and linked to your. The problem with comparing compacts is that most of the specifications only mention how close to the subject you can stick the lens, and not how small things can you actually capture. –  che Aug 7 '10 at 21:24
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Note that a big part of this, for compacts, is that they tend to have much smaller sensors, and thus have shorter focal-length lenses, which by their nature allow for a greater depth of field, which is highly useful for close-focusing -- the ones that make use of this can sometimes be "better" than an SLR giving you an image of the same sized subject, because you have greater depth of field with a lower aperture number. The trade-off is that you tend to be much closer to the subject -- perhaps even touching it with the barrel of the lens! (Not always great for photographing living things.) –  lindes Dec 9 '10 at 5:07

A macro lens is a lens that you can use to protograph on a relatively short distance, to take extreme closeups.

For a short focal length, that means as close as a few centimeters, for a long focal length it can be several decimeters.

The classical definition is that the image on the film plane should be close to, or larger than, life size. With digital cameras with smaller sensors it's hard to reach that definition, so some manufacturers uses the definition that a regular 10x15 cm print should be close to life size.

There are special macro lenses, but you can also use a extension tubes or close-up lens to give a regular lens macro capabilities.

Examples of macro photos; a bottle neck and a rowan flower. Notice the blurry background, which is common for macro photos as the background is so far away compared to the subject:

Bottle neck Rowan flower

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I believe that, at least in the DSLR space, the 1:1 ratio still exists. Some lenses have either a 'macro' mention on the distance scale, or a specific 'macro' setting, that are not 1:1 macro lenses, but that's just marketing. –  Dave Van den Eynde Aug 7 '10 at 14:36
    
@Dave: Good point. I changed the answer so that it's clear that the classical definition is not obsolete. –  Guffa Aug 7 '10 at 14:50

A macro lens is capable of focusing on things that are really close.

How close? (Magification ratios explained)

A 1:1 magnification means that a lens can focus on something so close, its image on the film/sensor is the same size as the subject itself, so you can imagine that's probably about as close to the lens as the lens is long (depending on the lens design). A lens with a 1:1 magnification ratio or greater is clearly a macro lens. Just to give you an idea, this level of magnification should allow you to get close enough to a 50 cent coin so it fills the frame, and still focus on it correctly.

As with all lenses, the closer you focus, the narrower the depth of field becomes in real terms. Macro photography is often characterised by a very narrow depth of field, creating a lot of background defocus (blurred background).

Macro lenses don't only do macro

Macro lenses are designed to be able to focus close, but that doesn't mean they can't focus out to infinity as well, and they may serve as a good portrait lens too. With very few exceptions, they can focus all the way to infinity. You don't have to use them for actual macro photography (that's something I never realised when I was new to SLRs).

Properties of macro lenses in general

A macro lens of a similar quality and design will typically be more expensive, because its ability to focus so close requires a few design considerations. It may also be slightly more bulky. It may, however, have better image quality in some respects, and not just when taking macro photographs. These are generalisations only and each lens is going to be different.

Lenses for portrait photography

As mentioned above, macro lenses can sometimes be used for portrait photography too. They often exist in focal lengths that would also be attractive to portrait photographers, and are often good quality lenses with low distortion and fixed focal length.

Traditionally, portrait photographers tend to like to minimise perspective distortion ("big nose effect") so they choose longer, rather than shorter, focal lengths and stand further away. For this reason, 100mm/105mm and 135mm primes are popular focal lengths for lenses marketed as "portrait" lenses, but this won't stop you using something as wide as a 35mm or as long as a 300mm for a portrait - it's about the look you want to achieve.

This is one example of a Macro lens that should be good for portraits.

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There is at least one current macro lens that does only macro, the Canon MP-E 65mm 1-5x Macro. That's not to say that you aren't generally right, most 50mm/100mm macros make pretty nice portrait lenses. –  Chinmay Kanchi Jul 31 '13 at 5:40
    
Thanks @ChinmayKanchi –  thomasrutter Jul 31 '13 at 6:10

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