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    Gringo's Avatar
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    Default Is the difference between F1.8 and F2.8 noticeable?

    Hey,
    I've been eyeing a purchase of a 50mm F1.8 lens for my Sony Alpha. I'd like to know if the difference of the amount of light that enters at the setting, in comparison for example with a F2.8 lens. Is the difference noticeable? Currenty I'm stuck with the basic 18-70mm F3.8 lens that came with the camera, so I'm sure more light is going to enter the lens, but I want to be sure if the F1.8 is worth the extra dollars (specially since it's a a fixed 50mm portrait lens, no zooming). I tend to take shots in dark environments, with low intensity light sources (like concerts, theater, etc).

    Thanks for the help!

    GRINGO.
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    Your F 1.8 lens lets in twice as much light as a 2.8-I stop difference,and four times as much light as your F3.8-2 stops difference.Regards.Ken

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    skatingzooyork is offline dPS Forum Member
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    I have a 10.5mm 2.8 fisheye and the 50mm 1.8 lens and there is a noticable difference when is comes to low light shooting. And the 50mm 1.8 is great for concert, theater, and portraits expecially for the price.

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    Yes but the question is do you need it, especially if money is a concern. You can boost the ISO from 200 to 400 which is equivalent to that one f-stop.
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    Just to be anal-retentive (and yes, I spell it with a hyphen), the difference between f/2.8 and f/1.8 is one-and-a-third stop.

    f/2 would be twice the light. (1 stop)
    f/1.8 is 2.5 times the light. (1.33 stops)
    f/1.4 would be 3 times the light. (1.66 stops)
    f/1.2 would be 4 times the light. (2 stops)

    It's a power-of-two thang.
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    And perhaps equally important for actual portrait work. Wide open, a 2.8 lens at 5 feet has a depth of field of roughly four inches. A 1.8 lens at 5 feet has a depth of field of just over an inch.

    Whether you WANT to be able to control depth of field that much is something to consider, and doing it by accident and having the tip of the nose in focus and the eyes and ears fading out is a real possibility.

    It's not quite what you asked, but it is a difference!

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    Quote Originally Posted by inkista View Post
    Just to be anal-retentive (and yes, I spell it with a hyphen), the difference between f/2.8 and f/1.8 is one-and-a-third stop.

    f/2 would be twice the light. (1 stop)
    f/1.8 is 2.5 times the light. (1.33 stops)
    f/1.4 would be 3 times the light. (1.66 stops)
    f/1.2 would be 4 times the light. (2 stops)

    It's a power-of-two thang.
    I was approximating, but,Whatever blows your dress up! Ken

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    crunch's Avatar
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    Quote Originally Posted by inkista View Post
    Just to be anal-retentive (and yes, I spell it with a hyphen), the difference between f/2.8 and f/1.8 is one-and-a-third stop.

    f/2 would be twice the light. (1 stop)
    f/1.8 is 2.5 times the light. (1.33 stops)
    f/1.4 would be 3 times the light. (1.66 stops)
    f/1.2 would be 4 times the light. (2 stops)

    It's a power-of-two thang.
    Sorry inkista, I'm the same.

    The "1.4" in f/1.4 is approx sqrt(2), which is a whole stop number. So the list is:

    f/2 would be twice the light as f/2.8. (1 stop)
    f/1.8 is 2.5 times the light. (1.33 stops)
    f/1.6 would be 3.2 times the light. (1.67 stops)
    f/1.4 would be 4 times the light. (2 stops)
    f/1.3 would be 5 times the light. (2.33 stops)
    f/1.1 would be 6.4 times the light. (2.67 stops)
    f/1 would be 8 times the light. (3 stops)

    f/1.2 is a half-stop, so that would be 5.7 times more light than f/2.8 (2.5 stops).
    Last edited by crunch; 11-20-2008 at 07:32 PM. Reason: correction on f/1.2

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    Quote Originally Posted by Mr Guy View Post
    And perhaps equally important for actual portrait work. Wide open, a 2.8 lens at 5 feet has a depth of field of roughly four inches. A 1.8 lens at 5 feet has a depth of field of just over an inch.

    Whether you WANT to be able to control depth of field that much is something to consider, and doing it by accident and having the tip of the nose in focus and the eyes and ears fading out is a real possibility.

    It's not quite what you asked, but it is a difference!

    May be a silly question but what happens at lets say 10 feet? Would the depth of field be larger? Like if your shooting a concert and you can't get 5 feet away, would you be safer at a further distance from getting a sharp nose and blury eyes?
    Nikon D700, Nikon D200, 50mm f1.8, 28-80mm, 28-75mm f2.8, 70-300mm 5 speedlights, some stands, umbrellas etc.
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    crunch's Avatar
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    Quote Originally Posted by sarahgirl777 View Post
    May be a silly question but what happens at lets say 10 feet? Would the depth of field be larger? Like if your shooting a concert and you can't get 5 feet away, would you be safer at a further distance from getting a sharp nose and blury eyes?
    The further the lens is focused (10 ft vs 5 ft), the greater the DoF (more will be in focus), for a given aperture.

    So yes.

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