What is a macro?

[ant_nio_marques]

Terribly naive question here.

 

We're told a macro is something that is able to focus at very small distances. I don't even know if there is something technical behind the

actual result (being able to focus closely). But then we also here a that macros have to be long so as not to have to photograph too

closely. What is it then? Ability to focus closely and then you're told to stay far from the subject?

 

Also, what is there in the lens that actually earns it the name 'macro'? Is it a rank attributed to a certain performance, or there is some

underlying property of the design?

[ellis_vener_photography]

Generally it is the ability to photograph at 1:1. Which is to say that that the length and width of the object on film or on the

sensor is the same as the length and width of it in the real world.

[Alan Marcus]

<p>Macro in photo jargon translates to a lens capable of imaging at life-size. This is magnification 1 (one) often called “unity” or expressed by the ratio 1:1 (one-to-one). Often a lens will be advertised as a “macro” however it may fall short of “unity”.</p>

<p>To understand you need to know that a typical camera lens is optimized to image objects at a far distance (infinity symbol ∞ meaning as far as the eye can see). When ordinary camera lenses are tasked to image at near distances they are slightly compromised. The degradation is minuscule so you may not notice.</p>

<p> Worse, at distances closer than 1 meter (1 yard), the f-numbers engraved on the standard lens barrel become invalid as you close focus. Should the ordinary camera lens be tasked to image at “unity”, the f-number error is 2 stops (4x less light transversing the lens). As to the standard lens being optimized for distance, it is figured to image a curved world and project that image on flat film or the surface of a digital imaging chip.</p>

<p>To close-focus, the camera lens must be moved forward increasing lens-to-film or digital chip distance. At ‘unity”, the lens extension will be one complete focal length. Since many cameras will not allow close-focusing, a workaround is to dismount the lens and use a spacer called a ring to increase lens to film or chip distance. Ring sets are sold with various size spacers to allow several close-focus magnifications. Often the standard lens is reversed. This points the back of the lens at the subject. The idea is, the back of the lens is optimized to focus on a flat surface and most close-up subjects are nearly flat.</p>

<p>Still the photographer must compensate for the f/# error. This problem is moot in a modern camera that meters exposure through the lens.</p>

<p>Macro lens to the rescue: The macro is optimized to image flat subjects at “unity”. The macro is slightly compromised when tasked to image distant subjects. This compromise is likely too small to be noticed. Most important, the macro design solves the problem of the f/# error (called bellows factor). The macro design uses a strong front lens element that magnifies the size of the lens aperture as seen from the front. This element moves as you focus -- thus the apparent size of the aperture is made adaptable; it compensates for light loss as the lens is close-focused. The modern macro is a marvel of technology. </p>

<p>The distance lens to subject at any given magnification is a matter of geometry. At unity, the subject is 4 focal lengths from the film or digital chip. The lens is extended and rests in the center. Thus a 100mm lens focused to unity, the subject to image plane is 400mm in separation, the lens is 200mm forward of the image plane and 200mm from the subject. Measurements are taken from a point within the lens barrel called the rear nodal.</p>

<p>Nobody said this stuff is easy. Hats off the modern opticians who now use computer software to design. Not too long ago it took years to do the math by pencil and paper using a slide rule and math tables</p>

[JDMvW]

<p>Under the learning tab, here, there are lots of resources.<br>

Although the one on Macro is old, it's a goodie.<br>

http://www.photo.net/learn/macro/primer </p>

[ant_nio_marques]

Thanks! I think Alan's detailed reply will be a nice google result in the future when someone else has the same question. I

know very little about optics but following the explanation was great!

 

As to the page in the learning section, it's nice but I was unable to find it by browsing.

 

It's very good that it explains the subject without photos of bugs. I simply can't stand looking at insects or arachnids. Other

bugs also give me an electrical shock to the spine, but then I can keep looking. But not those ones. I know no one else

with the same issue, but it is very serious for me.

[q.g._de_bakker]

To expand a bit, it may perhaps not help to point out (but maybe it does) that if a lens is to project a sharp image of a subject, there is a strict relation between the distances from lens to subject and lens to film and the focal length to fullfill.<br>It is expressed in the lens maker's formula: 1/focal length = 1/subject distance + 1/image distance.<br>So when the distance to the subject gets smaller, the distance to the film or sensor has to get bigger, or else there's no in focus image.<br><br>Is your subject infinitly far away (or close enough), 1/subject distance will be 0, and thus 1/image distance will be 1/focal length. So when set to infinity, the distance from lens to film or sensor is exactly the same as the focal length.<br><br>This also involves the relative sizes of the subject 'in real life' and of the image of the subject on film or sensor. The size in the image of such a subject infinitely far away will be infinitely (or close enough) small.<br>While reducing the lens to subject distance, the lens to image distance will increase. The ratio of the size of the subject in real life to the size of the image of the subject will reduce too: the two sizes will become more equal.<br><br>Gradually coming closer, there will be a point of symmetry, at which the distance from lens to subject is the same as the distance from lens to image, and the size of the subject and the size of the image of the subject will be the same too (1:1 scale, 1x magnification). And that is when both subject and image distance are 2x the focal length (1/f = 1/2f + 1/2f, right?)<br>From that point onwards, things are a mirror image of what went on before reaching the point.<br><br>What keeps getting worse is light loss. When you move the lens away from the film or sensor, the light leaving it will be spread over increasingly large areas, i.e. gets spread out thinner. The image will get dimmer.<br>Alan mentioned modern macro lenses, and what they do instead of increasing the distance from lens to film is what the lens maker's formula also allows: reduce the focal length. That way the relative lens to image distance increases even though the real, physical distance does not. It's a trick made possible by modern computer power.<br><br>What makes a true macro lens is not (!) that you can get to 1:1 without aids or trickery.<br>It is that it projects an image of high quality when used in the range where both subject and image distances aren't that unequal as they are when taking pictures of subjects at a moderate to large distance away from the lens. So the fact that you may need "rings" (they are called "extension tubes" most of the time) or bellows extension (a variable version of extension tubes) does not mean a lens cannot be a macro lens.<br>Calculating a lens formula such that the result is a lens that projects a high quality image is a lot of work. Now that computers have taken over, it is possible to calculate complexer lenses than before (took too much time without computers), so that such tricks as ever changing lenses, i.e. lenses that do change their focal length when focussing, are possible. The bits of glass shifting relative to each other do not just do that to reduce focal length, but also to maintain image quality as high as possible when doing so.

[dhbebb]

<p>Traditionally photomacrography has involved photographing objects at magnifications from around 1:2 (half life size) to 10:1 or so. In the laboratory cameras like this<br>

<a href="http://4.bp.blogspot.com/-hc9eQZMsiDY/TsCMPG_9p0I/AAAAAAAAD-o/Xw0FogPHNj8/s1600/P1010441.jpg">http://4.bp.blogspot.com/-hc9eQZMsiDY/TsCMPG_9p0I/AAAAAAAAD-o/Xw0FogPHNj8/s1600/P1010441.jpg</a><br>

are used, the essential features being a long bellows, a lens corrected for high magnifications and, most important, a macro rack which allows focusing by moving the whole camera. To allow reasonably close focusing on 35mm size cameras without a bellows, lenses have traditionally been made in 50 or 60 mm focal length, since these require only 50 or 60 mm extension (achieved with a helical focusing mount) to photograph at 1:1. For certain special purposes, such as medical photography, designed to take pictures during operations, a longer focal length is essential to keep the photographer out of the surgeon’s way:<br>

<a href="http://cameraquest.com/nf200med.htm">http://cameraquest.com/nf200med.htm</a><br>

but in general a macro lens these days is a prime lens designed to photograph at up to 1:1 OR a zoom lens that focuses closer than usual (very often up to 1:2). </p>