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Pictures with a magnifying glass

The magnifying glass is the most used optical instrument. It is not the prerogative of only Sherlock Holmes-like detectives or lepidopterists. It is commonly used for precision work or to decipher details too small to be seen with the naked eye. Placed in the field of a camera, it provides surprising effects.

A simple magnifying glass provides a thousand possibilities to magnify, distort or surprise our ocular vision.
The distance between the optical center of the magnifying glass and its focus defines its focal length. It can be estimated by placing the magnifying glass in such a way that it projects on a flat surface an image of an object located at infinity (in practice, the object can be located at least 5 m away). Measure the distance between the magnifying glass and the projected image to obtain the focal length. Here the distance is 17 cm between the magnifying glass and the wall.

Biconvex Lens

The inventor of the magnifying glass is unknown. Archaeologists have found transparent, rounded and polished stones, made more than three thousand years ago. From a scientific point of view, the magnifying glass is a simple optical instrument composed of a biconvex lens, whose two faces are curved. The light rays coming from a distant object pass through the lens. They converge in a point called focus.

The distance between the optical center of the lens and its focus defines its focal length. When a magnifying glass is used, it is always placed near the object to be magnified. The object is then between the focus and the lens. The image appears right side up. If, in place of our eye, we install a camera equipped with a lens (standard or macro, it doesn’t matter), the photographed image is magnified, too, without inversion.

Still Life
Whether you place a magnifying glass of small diameter or large diameter in front of the lens in close-up shooting, it is recommended to work with the camera placed on a tripod.
Without Magnifying Glass
The shot is made with a 12-45 mm zoom lens (set at 30 mm, f/5.6 aperture) on an Olympus OM-D E-M1 Mark II camera. The light comes from a bay window. The camera is fixed on a tripod.
With Magnifying Glass
A magnifying glass of medium diameter (75 mm) is placed between the lens in macro position and the object. You can modify the position of the magnifying glass and the object to obtain different effects.

Stunning Vision

When the object is beyond the focus, at a distance greater than the focal length, the image is reversed. If a camera lens were replaced by a magnifying glass, the image would be projected onto the film or sensor in reverse after focusing, just as a camera lens would. But a biconvex lens delivers a lower quality image because of its chromatic and geometric aberrations.

At The Front Of The Lens

The upside-down image created by a magnifying glass can be photographed with a standard or macro lens mounted on the camera, by moving the magnifying glass away from the object and towards the lens. The most spectacular effects are obtained by photographing the image of distant objects observed with the magnifying glass placed in the field of the lens: everything is blurred apart from the inverted image produced by the magnifying glass.

From a practical point of view, the larger the diameter of the magnifying glass, the more it will cover the observed field. That said, interesting effects can be obtained with all kinds of diameters. Note that the colored fringe of chromatic aberrations produced by biconvex lenses provides an aesthetic touch that is undeniable.

Outside, the magnifying glass produces surprising effects. Here is a cityscape. Nikon D850 and 24-120 mm zoom.
Focusing On The Magnifying Glass
The 24-120 mm zoom is set to 120 mm (f/8). Focusing is made on the mount of the magnifying glass with a diameter of 10 cm, placed at about 70 cm from the camera. Apart from the mount, everything else in the image is blurred.
The Upside Down Image
The focus must be made between the magnifying glass and the lens in order to obtain a sharp image. As the magnifying glass is far from the observed subject, at a distance greater than the focal length of its lens, the image appears upside down.

Diopter And Focal Length

The power of a lens is technically expressed in diopters (the unit of measurement of vergence of optical systems). Spectacles for presbyopes are referenced in diopters. Commercial hand-held magnifiers indicate their magnification: 2x (4 diopters), 3x (8 diopters), 4x (12 diopters), etc. The focal length of the magnifier is determined by dividing the diopter by 1000. The result is given in mm. 8 diopters/1000 = 125 mm.

Regardless of these considerations, we see that the more the lens is curved, the more it magnifies the image. And generally, the more curved the lens, the smaller its diameter and the narrower its field of view. Magnifiers with a large diameter, about ten centimeters, with a magnification of 3x to 4x are very well suited to photographing with a magnifying glass.

Discover the photography courses at Spéos

Spéos offers various training courses ranging from simple one-week photography courses (initiation and advanced level) to 3-year courses. The long courses to become professional photographers allow you not only to master all the photographic techniques and its vocabulary (blurs, hyperfocus, sharpness zone, depth of field, backlighting, focal length, shutter release, autofocus, wide-angle, rule of thirds, etc.), but also all the stages of shooting and image processing.

Visiting the school allows you to discover the premises, the studios and the equipment, and is undoubtedly the best way to familiarize yourself with your future way of working. This is why, in addition to the open days, Spéos offers throughout the year personalized visits by appointment to come and discover the school with a member of the team.

Text and photos: Philippe Bachelier, teacher of Printing techniques at Spéos

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