However they do not have a means of reducing the amount of light coming into the binoculars and the amount that comes out for your eye to see. It has a constant f-ratio of, let's say f4. Do you have a binocular at home that you use? It is just a lens. This is why you may see a photograph with f/9 on the EF 24-105mm f/4L IS USM in your sample picture or an f-stop of f/22 on the EF-S 18-55mm. If you are using a shooting mode that allows the camera to select an f-stop for you, then the camera may select larger f-stops for your lens in brighter scenes like outdoors on a sunny day. This is more commonly known as a variable aperture lens. The first f-stop in the lens name corresponds to the minimum focal length of that zoom lens and the second f-stop in the lens name corresponds to the longest focal length for that lens. At 18mm, that lens has an f-stop range of f/3.5 to f/22 and at 55mm, that lens has an f-stop range of f/5.6 to f/38. Your less expensive EF-S 18-55mm f/3.5-5.6 lens is named that way because at 18mm, the smallest f-stop is f/3.5 and at 55mm, the smallest f-stop is f/5.6. Since the EF 24-105mm f/4L IS USM can have an f-stop as small as f/4 throughout its entire focal length range, you only see one f-stop in its name. The name of the lens only includes the smallest possible f-stop for the entire range of focal lengths the lens can cover. This entire range of f-stops is available at any focal length on that lens. When you are zoomed out to 55mm, the maximum setting is only f/5.6.Ī constant aperture zoom does not change the maximum available aperture as you zoom from one end of the range to the other end of the zoom range.įor Glenn, your EF 24-105mm f/4L IS USM has an f-stop range of f/4 to f/22. At 18mm, the maximum aperture can be set as wide as f/3.5. This means that the maximum aperture changes as you zoom from 18mm to 55mm. Sometimes you will see the aperture expressed on a zoom lens as two values like the EF-S 18-55mm f/3.5-5.6 IS STM. Apertures can be set to narrower sizes than maximum, which is also known as "stopping down" the aperture. Sometimes you will see the aperture described as a ratio, Instead of seeing " f/4 ", you might see " 1:4 ". The smaller the number, the smaller the ratio, which means the wider the aperture.Įvery lens should have its' maximum aperture printed on it somewhere. The aperture values that you see in the model number is the widest aperture setting that the can provide. help?Īperture describes a ratio of certain physical dimensions within the lens. On my amature DSLR camera that has lens 18-55mm f1.5-5.6 when using aperture priority, I can set the f-stop to f/22 for instance. As you can see the author took the picture are f/9 while the lens itself has a max aperture of f/4. so my expectation when I look at the info through my viewfinder I should see f/4 all the time, but this is not the case. For instance, lens like EF 24-105mm f/4 L, my understanding is the aperture is constant at f/4 regardless whether it is zooming or out. I do not understand how can the f-stop inside the camera can be set to bigger than the max value of the lens' aperture. I am confused with the relationship between the constant aperture number found in some luxury lens and the f-stop/f-number that is shown in the camera itself. So, here hopes some experts can demistify this fog. Another beginner's question that confused me alot.
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