![]() You’ll most likely have to use whatever lenses you already have. In normal usage I would regard this very same lens to be one of the sharpest EF lenses that Canon have ever made, so it just goes to show that not all lenses take well to being operated outside of their designed parameters.įor many people, the whole point of using extension tubes is so that you don’t have to buy a new (macro) lens. Close examination of my 24-70mm images showed considerable distortion and loss of fine detail. The “nifty fifty” actually performed much better in terms of overall sharpness with extreme extension. Extension tubes have the effect of magnifying these imperfections on the sensor, so if you start with a lens that performs poorly at the MFD, you’re going to notice it pretty quickly once you start using the tubes.Ī great example of this is found in the section further down this guide where I tested the $130 Canon 50mm f/1.8 STM with extension tubes, and the $2300 Canon 24-70 f/2.8 L II with the same tubes. What all this means is that every lens performs differently at the MFD, and you can’t necessarily trust that an expensive, well regarded lens is going to be super sharp at the MFD. Conversely, super telephoto lenses tend to be used for focussing on objects that are quite some distance from the lens, so the opposite is true. Often a macro lens is at its absolute sharpest when used at the MFD. Take a macro lens for example The designers know that it’s going to spend much of its time being focussed at the absolute closest focus point, so they correct distortions for that point. The result is that some lenses are sharper than others when they are used at the minimum focus distance. Lens designers try as hard as they can to correct for distortion at the most important points in the focal range of a lens. Focusing a lens does move the optics inside a lens, so that usually means that the amount of distortion varies depending on how far away your subject is from the lens. When manufacturers design the optics inside a lens, they take into account distortion and try to correct for it as much as possible. The tricky thing about this point is that every lens reacts very differently to using extension tubes, so it’s hard to deliver a sweeping answer to this question. This means that in most circumstances they have very little effect on image quality. ![]() Unlike teleconverters, extension tubes have no optics in them at all. How Do Extension Tubes Affect Image Quality? Instead it’s something you need to carry in your bag and use when it makes sense to do so. It’s for this reason that you should generally not leave an extension tube in place all the time. This has few practical implications because most people are using extension tubes to try to focus on something at a very close distance, but it’s worth knowing so that you don’t think your lens is broken when you find it’s no longer able to focus on something further than a few feet away. Later in the article I will discuss the knock-on image quality issues caused by extension tubes, but the other important thing to realise is that when extension tubes are in place, you can no longer focus all the way to infinity. What all this means is that you can turn a normal lens into something with much a much higher magnification factor to achieve macro-like images, without needing a dedicated macro lens. ![]() The thicker the extension tube used on a lens, the higher the lens magnification becomes as you’re able to move the lens much closer to the subject and still achieve focus. If a subject is closer to the sensor than a lens’ MFD, you cannot focus on that subject. The MFD of a lens is a measurement of the closest point a subject can be from the camera’s sensor, whilst still being able to focus. Extension tubes can turn any lens into a macro lens.Īn extension tube is a spacer that sits between your lens and the camera body to alter the MFD (minimum focus distance). ![]()
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