5 replies to this topic

[Jeremymwilson]

Hi everyone, I have tried to find the answer to this question using google but no luck.

So I bought the Nikon 50mm 1.8g for my D90 (I love it already) but I thought that the 1.8 meant that the lens was always at that aperture so why am I able to change the aperture in camera? For instance if I set the camera to auto it will change the f stop depending on available light, just like my old kit lens.

I know this is very basic stuff...thanks for your kindness and patience 😊

[TKC_TX]

The listed aperture on a lens is the maximum it will go to. Other than some very specialized lenses, the aperture can always be adjusted.


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[Merco_61]

The f/1.8 designation is the widest the aperture can go, you can stop it down as needed. In fact, it is sharper and has better contrast closed down a bit to the f/2.2-f/2.8 region. As you get to know your new lens, play around with the aperture some and learn to see how a change of aperture changes the depth of field. Previsualizing both field of view and DOF comes with learning each lens and makes it much more enjoyable to use. Being able to open the aperture up for a shallower DOF is one of the nicer things about these fastish prime lenses. Making this previsualization instinctive is a big part of the good things about my One week, one camera and one focal length exercise over in the mini-challenges subforum.

[TKC_TX]

I guess I should add that when a lens has two apertures listed it means that the maximum aperture available Changes as the lens zooms in or out. The aperture cans still be changed at any focal length, only the maximum available is reduced as you zoom to the longer focal lengths.


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[Jerry_]

Something else to add is that the (auto-)focussing is done with the widest aperture open, in order to have a max of light coming in to determine the best contrast. Then the aperture is closed to whatever it is set when the capture is taken.

Thus having max aperture (wide open) with a value as small as possible, i.e. 1.8 is better than 4, will allow to have better focus results in low light situations.

[Jeremymwilson]

The f/1.8 designation is the widest the aperture can go, you can stop it down as needed. In fact, it is sharper and has better contrast closed down a bit to the f/2.2-f/2.8 region. As you get to know your new lens, play around with the aperture some and learn to see how a change of aperture changes the depth of field. Previsualizing both field of view and DOF comes with learning each lens and makes it much more enjoyable to use. Being able to open the aperture up for a shallower DOF is one of the nicer things about these fastish prime lenses. Making this previsualization instinctive is a big part of the good things about my One week, one camera and one focal length exercise over in the mini-challenges subforum.

Great, thanks it's a lot clearer now.