Conversely, it is easier to use more powerful close-up lenses on shorter focal length lens. A +4 diopter lens will provide more additional magnification on a 105 mm lens than on a 50 mm lens. Short focal length lenses will require more power to get the same added magnification when compared to a longer focal length lens. The amount of magnification achieved with close-up lenses tends to be modest and varies with the focal length of lens and the power of the close-up lens. A +4D lens will have a focal length of 250 mm. The diopter measurement can be converted into a focal length by dividing 1000 by the power in diopters. The power of a close-up lens is measured in diopters (D), the same unit of measurement that eyeglasses are measured. Either of these situations leads to increased lens aberrations and a potential decrease in image quality. That means that you should be able to resolve smaller details on your images with close-up lens than you would have by just increasing the magnification by the use of increased extension.Īgain, this improvement is all predicated on the assumption that the lens is of a high-quality and that the power of the close-up lens is not too high for the lens it is being added to. The end result is that the resolution you will see at the detector is similar while the magnification increases. The f/number decreases because the focal length shortens, while the entrance pupil is slightly enlarges. In order to get increased magnification at the same effective aperture, the f/number of the lens needs to decrease. That means that the effective aperture is completely unaffected. The exit pupil size and its distance from the detector are unchanged. Close-up lenses only affect the amount of glass in front of the aperture, i.e. Increased effective aperture means more diffraction and less image quality. With most other methods, increasing the magnification will cause the effective aperture to also increase. So, longer focal length macro lenses and higher power close-up lenses will tend to make the image quality worse.Ī big benefit of using an close-up lens is that the image magnification increases but the effective aperture doesn't change. Lens aberrations become a bigger issue as the power of the lens is increased or if the focal length of the lens being modified is increased.
This increase in aberrations is at least partially counteracted by the benefits of adding one of these lenses. The added glass of the close-up lens does tend to cause increased aberrations within the system, potentially decreasing the resolution capabilities of the lens it is being added to. A shorter focal length with the same extension causes the image to be more magnified. The amount of extension has not changed (actually there is a slight change as the principal planes will move a little with the added lens, but we'll ignore that). They primarily work by shortening the focal length of the lens. How do close-up lenses work?Ĭlose-up lenses work in a couple of different ways to increase the magnification and potentially the resolution of a lens. I find this to be a win-win situation for adding modest amounts of magnification. Since these lenses don't cause the effective aperture to rise (worsen), a sufficiently high-quality lens you will get the added magnification with very similar image quality. Most other methods of adding magnification cause the effective aperture to increase which will negatively affect the resulting resolution capabilities of the lens. The advantage of adding magnification this way is that the close-up lens doesn't affect the effective aperture of the lens. Need to match the size to the lens you are mounting it on, you may need adaptersĬlose-up lenses work by shortening the focal length of the lens which will allow for closer focusing and more magnification.
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