Macro

Macrophotography (often called "macro-photo" or "macro") represents, in the minds of many photographers, the close-up photo.

Definition

Magnification is the ratio of the size of the image on the camera sensor to the actual size of the subject being photographed.

The magnification M = Image / Object

Examples:

  • A 2 in photographed object with an image measuring 1 in on the sensor will give a magnification ratio of ½ (often noted as 1:2) or a magnification factor of 0.5x
  • If the image of this object measures 2 in on the sensor, the magnification ratio will be 1/1 (1:1) or a factor of 1x

The scientific definition of macro photography

A true macro lens will have a fixed focal length that achieves a magnification factor of at least 1.

Many standard zooms are called "macro" but in reality they are not macro objectives in the strict sense of the term because they do not achieve the magnification of 1. With these objectives you can do only the proxy-photography.

How to increase the magnification factor of your lens?

There are photo accessories that can increase the magnification factor of a lens. We will see 2 here.

1) Lens close-up

A close-up lens is a converging lens that adds to a lens, increases the deviation of light rays and thus brings the focus plane closer together. We can get closer to the subject to photograph and therefore enlarge it further (increase the magnification).

Depending on the power (expressed in diopters) of the close-up lens, you can approach more or less close to your subject and thus more or less enlarge the image obtained.

The first time you use a close-up lens, you may be surprised by its particular mode of operation: once screwed to your lens, you will not be able to focus on even a few distant subjects (the focus will not be beyond 40 inches and even well before in most cases). You do not have alternatives, you must use the close-up lens for its first and only function: to do close-up photography, proxy-photography or macro photography.

The table below gives the magnification obtained with a close-up lens according to the power of the lens in diopters and the focal length of the lens used.

The calculated focus distance and magnification are those obtained with the focus ring set to infinity. This means that with the ring set to the minimum focus distance of the lens, you can get even closer to your subject and thus achieve a magnification even greater than that shown in the chart.

Attention, the calculations are theoretical and the result, even if it gives a good order of magnitude, remains approximate (they are based on the assumption of a simple optical formula to a lens).

2) Extension tube

The extension tube is a hollow tube devoid of optical elements that is placed between the optics and the housing. It allows (by lengthening the distance to the optics) to reduce the minimum distance of focus and thus increase the magnification. It keeps the autofocus and the measurement of the light. Be careful not to confuse them with zoom magnifiers, which allow them to increase the focal length of your lens, but does not affect the minimum focus.

There are several thicknesses and the thicker the ring, the closer you can get to the subject and get it enlarged on the picture. It is also possible to mount several rings on top of each other for even greater magnification.

The big disadvantage of the extended rings is that the depth of field will be reduced.

Comparison of magnification with a lens close-up and with an extension tube

Use

Close-up lens

1. Choose the desired unit for the results

2. Set the focal length, the value of your close-up lens and the focus distance you want by turning the wheel or by clicking to enter the value

In the bottom area

3. You get:

  • The diopter value of your set (lens + close-up lens)
  • The minimum focus range in relation to the subject
  • The magnification value that will be obtained
  • The size max. of the object so that it remains visible in full on the image

Extension tube

1. Choose the desired unit for the results

2. Adjust the focal length, the value of your extension tube and the focus distance you want

In the bottom area

3. You get:

  • The value of the diopter of your set (lens + extension tube)
  • The minimum focus range in relation to the subject
  • The magnification value that will be obtained
  • The size max. of the object so that it remains visible in full on the image