Extension Tubes and Close-up Lenses for Macro Photography
A guide to using extension tubes and close-up lenses for macro photography; practical advice, and the pros and cons of these photographic accessories.
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Extension tubes and close-up lenses are accessories used in macro photography. They are often utilized by amateur photographers with a limited budget. Since a macro lens is expensive, it’s reasonable to explore this genre by spending as little as possible with appreciable results, to decide later if it’s something we want to pursue.
Let’s start with close-up lenses. These are mounted onto the camera lens to increase the magnification factor. For compact cameras, it’s necessary to purchase adapter rings.
Multiple lenses can be combined to achieve greater magnification. However, it’s advisable to mount the most powerful lens first.
The dioptric power, indicated on the edge of the lens as +1, +2, +4, etc., measures the lens’s magnifying power and affects image quality:
- Low Diopters (+1 to +3): Lenses with low diopters, like +1, +2, and +3, are generally suitable for slight magnification. These lenses induce fewer optical aberrations, making them suitable for photographers who seek a slight change in their macro capability without significantly compromising image quality.
- High Diopters (+4 and above): As the diopter increases, like in the case of +4 lenses or higher, there’s a higher risk of optical aberrations, particularly chromatic aberrations. These aberrations can degrade image quality, making the image less sharp and possibly causing color distortions at the edges.
- Lens Quality: To minimize the introduction of aberrations, it’s crucial to choose high-quality close-up lenses. The best quality lenses are made from bonded achromatic doublets, which help reduce optical aberrations and maintain image sharpness.
- Combined Use of Lenses: It’s possible to combine close-up lenses of different powers to achieve greater magnification. However, care must be taken in the sequence of mounting the lenses, as aberrations can accumulate when stacking one lens over another. Therefore, it’s advisable, if possible, to use a single lens with greater magnifying capability to avoid a decrease in image quality.
Advantages of close-up lenses:
- They do not absorb light.
- They allow for closer proximity to the subject.
Extension tubes, unlike close-up lenses, increase subject magnification and decrease the minimum focusing distance by increasing the distance between the lens and the sensor (they are inserted between the lens and the camera body). They contain no lenses and are often available in sets with different lengths, for example, 12mm, 20mm, 36mm. They can be used individually or combined for varying degrees of magnification. Using longer tubes or combining multiple elements together decreases the amount of light hitting the sensor and can affect the depth of field, so it’s necessary to balance the tube length with the specific shooting requirements.
Extension tubes are equipped with electrical contacts that allow the lens and the DSLR to communicate for maintaining exposure automation and autofocus.
The millimeters (mm) indicated on the extension tubes refer to their length. This aspect is crucial because the length of the extension tube directly influences the degree of magnification and the minimum focusing distance of the lens. The longer the tube, the greater the magnification of the subject.
Disadvantages of extension tubes:
- Using them requires detaching the lens, exposing the sensor to dust.
- There’s a reduction in brightness of about 1-2 stops.
- Focusing becomes more difficult because the scene in the viewfinder will be darker.
Comparative advantages of close-up lenses over extension tubes:
- They are less expensive than extension tubes.
- They do not cause a reduction in brightness.
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