Why do compact cameras quote much shorter minimum focus distances than interchangeable-lens cameras?
Asked 8/21/2016
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My Canon PowerShot SX60 HS claims a minimum focus distance of 0 cm, while Micro Four Thirds lenses—including some macro lenses—are often listed around 10–20 cm. Why do compact cameras seem able to focus much closer? Is there an optical or mechanical reason interchangeable-lens lenses rarely have such tiny minimum focus distances?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
9y ago
2 Answers
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Because most interchangeable lens cameras typically use larger-format sensors than 1/2.3"-format.
The close-focusing capability of most small-sensored compacts comes from the fact that small sensors use proportionately short lenses. Very short lenses (those under 10mm focal lengths) tend to have very deep depth of field--deep enough to have close focus capability. "Macro mode" on a P&S camera is simply changing the focal distances the camera will search through. While your SX60HS has an "equivalent" focal length of 21mm at the wide end, the actual focal length of the lens's wide end is only 3.8mm.
A four-thirds (4/3"-format) or APS-C format sensor is roughly 4 to 6 times larger than a 1/2.3" format sensor, and requires lenses that are 4 to 6 times longer. The longer a lens is, the thinner the depth of field becomes at similar aperture settings, and the larger the minimum focus distance gets. This is one of the tradeoffs of using a larger sensor. And it's why you don't see macro modes on interchangeable lens cameras.
Originally by user27440. Source · Licensed CC BY-SA 4.0
user27440
9y ago
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Mostly because the numbers are not directly comparable, and because small-sensor cameras use much shorter actual focal lengths.
Compact cameras often have tiny sensors, so their lenses are physically very short at the wide end. Short focal lengths naturally give very deep depth of field and can focus very close. A “0 cm” macro spec on a compact is usually at the wide end and may be measured from the front of the lens, not from the sensor plane.
Interchangeable-lens cameras use much larger sensors, so they need longer actual focal lengths for the same angle of view. Longer lenses generally need more extension between lens and sensor to focus close. To reach high magnification such as 1:1 macro, the lens must move significantly farther from the sensor, which makes the optical and mechanical design larger and more complex.
Also, many interchangeable-lens specs measure minimum focus distance from the sensor plane, not from the front of the lens. That alone can add several centimeters.
So compact cameras do not magically break the rules: their short quoted distances come from tiny sensors, very short lenses, wide-angle “macro” modes, and different measurement conventions.
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