Extreme Macro Photography. Greater than 1:1. by Meyer Franklin. Extreme Macro Photography. What is 1:1? Macro image magnification is often defined in terms of a ratio (a.k.a. fraction).
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Greater than 1:1
by Meyer Franklin
What is 1:1?
Macro image magnification is often defined in terms of a ratio (a.k.a. fraction).
A ratio of 1:1 is considered the standard minimum magnification for true macro images. These images are also called "life size", where the size of the image of a subject on the sensor (numerator) is the same as the actual size of the subject (denominator).
How are images of 1:1 or greater achieved?
A reversing adapter can mount to your camera body, then a lens can attach to the adapter via the filter thread. A wide angle lens is designed to capture a huge landscape that is at infinity focus onto the camera image sensor. When reversed, a tiny subject at about 1 - 2 inches away is projected out to that huge landscape sized image... but it is cropped by the image sensor.
Example: A reversed 28mm f2.8 lens can get better than 2:1.
The Tamron 90mm, Sigma 105mm, Nikon 105mm, Pentax 100mm, etc. are examples of macro lenses that are capable of 1:1 macro images. The design of a macro lens builds in sufficient extension to attain the capture of 1:1 images without any additional components.
There are other ways to increase extension of any lens.
Extension Tubes and Bellows are common components for increasing extension of a lens.
Extension tubes are simply fixed length spacers that fit between your camera and lens; they contain no optics. They may be stacked together to provide more extension for longer focal length lenses and can also be used in conjunction with teleconverters to provide closer focusing than possible with a lens/teleconverter combination.
Reproduction ratio = focal length of lens/amount of extension
Example : 100mm lens/50mm extension = 1:2 (or half life size) - the same extension for a 200mm lens would yield 1:4.
Extension tubes generally come in fixed lengths. Bellows by there very nature provide variable amounts of additional extension. Due to their construction, most do not mate electronically with the attached lens, limiting functionality on many camera bodies.
Diopters (Closeup lenses)
A diopter is a magnifying lens element that mounts by screwing it into the filter ring of your existing lens. They are inexpensive and easy to use. Diopters may be stacked on top of each other for added magnification. When stacking diopters, always place the strongest diopter closest to the lens. Diopters involve the addition of extra layers of glass so they may marginally affect image quality, but on the bright side they do not cost you any light loss.
Stacking Lenses (Macro couplers)
Lens stacking has the same effect as using diopter or closeup lenses. A longer focal length lens is mounted on the camera and a shorter focal length lens is reverse mounted to it's filter ring using a lens stacking ring (macro coupler).
Magnification factor = Focal length of main lens / Focal length of reversed lens
200mm / 50mm = approx. 4X magnification (4:1)
Depth of Field
The greater the magnification used, the shallower your depth of field becomes. The old rule of choosing the smallest aperture possible stands true, but only to an extent. At apertures of f/22 or f/16, a loss of general image sharpness can occur through diffraction.
DOF = (2cf (M+l)) M2
c = circle of confusion (0.026mm for 35mm format * )
f = aperture and;
M = magnification
The distance from the end of the lens to the subject is known as the working distance. The working distance can be increased by using higher focal length lenses. It is decreased by adding extension (tubes or bellows). A reversed lens will set the working distance to a fixed (very short) working distance.
Most techniques for increased magnification will also result in a huge loss of available light. In addition, to improve depth of field, you will need to set a higher f-stop, which further reduces the available light reaching the sensor or film.
For proper exposure, you will need to reduce the shutter speed or increase the light on the subject. When your subject is moving, adding light is your only choice. The quality of the light will make a difference on the quality of the images.
Putting it all together
Teleconverter + extension tube + lens +stacked lens
Bellows + reversed lens
Try different combinations to see what works best for each image opportunity.