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Thread: Faster lens are brighter...BUT HOW? :O

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    Default Faster lens are brighter...BUT HOW? :O

    Can anyone explain this phenomena?
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  2. #2

    Default Re: Faster lens are brighter...BUT HOW? :O

    Quote Originally Posted by machiavellian View Post
    Can anyone explain this phenomena?
    To understand this, its very simple. You take 2 lens:

    a) Your kit lens 18-55mm F3.5-5.6.
    b) 50mm F1.8

    1st Step: You mount ur kit lens 18-55mm F3.5-5.6 onto ur camera.
    2nd Step: Zoom ur kit lens all the way to 55mm. The apeture of the lens is now at F5.6.
    3rd Step: Look through ur camera viewfinder. You should find that it looks quite dark.
    4th Step: Remove ur kit lens 18-55mm F3.5-5.6 & mount ur 50mm F1.8 lens
    5th Step: Look through ur camera viewfinder. You should find that it looks much brighter.

    This is the meaning of Faster lens are brighter.

    Faster Lens = the apeture of the lens is very big to allow tonnes of light to fall through = brighter view in the viewfinder.

    Now you get it?

  3. #3
    Senior Member sinned79's Avatar
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    Default Re: Faster lens are brighter...BUT HOW? :O

    this will speed up your understanding.



    peep at the hole and imagine you are light entering this hole.

    small hole = ?
    big hole = ?

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    Member makolit's Avatar
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    Default Re: Faster lens are brighter...BUT HOW? :O

    Quote Originally Posted by sinned79 View Post
    this will speed up your understanding.

    peep at the hole and imagine you are light entering this hole.

    small hole = ?
    big hole = ?
    perfect.
    is using a digital camera that works ...

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    Moderator daredevil123's Avatar
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    Default Re: Faster lens are brighter...BUT HOW? :O

    Quote Originally Posted by machiavellian View Post
    Can anyone explain this phenomena?
    Bigger aperture let in more light. More light means brighter.

  6. #6

    Default Re: Faster lens are brighter...BUT HOW? :O

    What have you been doing all these while ??

  7. #7

    Default Re: Faster lens are brighter...BUT HOW? :O

    F stop = focal length / aperture diameter
    Canon 6D | Canon 450D + Grip | EF 28 F1.8 | EF 85 F1.8 | Nissin 866 Flash

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    Senior Member Override2Zion's Avatar
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    Default Re: Faster lens are brighter...BUT HOW? :O

    Quote Originally Posted by machiavellian View Post
    Can anyone explain this phenomena?
    If your camera features a DOF preview button, set to various apertures and use that preview button while looking through the viewfinder, you will see for yourself.
    Nikon D200/D700/D800 User :)
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  9. #9

    Default Re: Faster lens are brighter...BUT HOW? :O

    This is on true if same exposure time is applied.

  10. #10

    Default Re: Faster lens are brighter...BUT HOW? :O

    Quote Originally Posted by ismokeweed79 View Post
    What have you been doing all these while ??
    i been smokin weed man!
    --

  11. #11

    Default Re: Faster lens are brighter...BUT HOW? :O

    Quote Originally Posted by devilry View Post
    To understand this, its very simple. You take 2 lens:

    a) Your kit lens 18-55mm F3.5-5.6.
    b) 50mm F1.8

    1st Step: You mount ur kit lens 18-55mm F3.5-5.6 onto ur camera.
    2nd Step: Zoom ur kit lens all the way to 55mm. The apeture of the lens is now at F5.6.
    3rd Step: Look through ur camera viewfinder. You should find that it looks quite dark.
    4th Step: Remove ur kit lens 18-55mm F3.5-5.6 & mount ur 50mm F1.8 lens
    5th Step: Look through ur camera viewfinder. You should find that it looks much brighter.

    This is the meaning of Faster lens are brighter.

    Faster Lens = the apeture of the lens is very big to allow tonnes of light to fall through = brighter view in the viewfinder.

    Now you get it?
    mm so would it be the same if the 50 f1.8 is stopped down to f5.6 as with the kit lens at 55mm, f5.6?
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  12. #12

    Default Re: Faster lens are brighter...BUT HOW? :O

    Quote Originally Posted by machiavellian View Post
    mm so would it be the same if the 50 f1.8 is stopped down to f5.6 as with the kit lens at 55mm, f5.6?
    I think u are understanding it already, it would be the same

  13. #13

    Default Re: Faster lens are brighter...BUT HOW? :O

    Quote Originally Posted by devilry View Post
    I think u are understanding it already, it would be the same
    thank you.
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  14. #14

    Default Re: Faster lens are brighter...BUT HOW? :O

    Quote Originally Posted by sinned79 View Post
    this will speed up your understanding.



    peep at the hole and imagine you are light entering this hole.

    small hole = ?
    big hole = ?
    thanks man!
    --

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    Default Re: Faster lens are brighter...BUT HOW? :O

    Quote Originally Posted by machiavellian View Post
    mm so would it be the same if the 50 f1.8 is stopped down to f5.6 as with the kit lens at 55mm, f5.6?
    The view finder is still as bright as f/1.8 for the 50mm prime eventhough you stop down to f/5.6. It will only affect the picture you took, not the amount of light entering lens for view finder or focusing. Correct me if i'm wrong.

  16. #16

    Default Re: Faster lens are brighter...BUT HOW? :O

    Quote Originally Posted by Jamesf View Post
    The view finder is still as bright as f/1.8 for the 50mm prime eventhough you stop down to f/5.6. It will only affect the picture you took, not the amount of light entering lens for view finder or focusing. Correct me if i'm wrong.
    I don't think so. T-stops (not f-stops) for lens of different constructions are different. The number and type of lens elements will affect the amount of light reaching the view finder. Maybe not visually very significant, but it will be there.

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    Default Re: Faster lens are brighter...BUT HOW? :O

    Quote Originally Posted by sinned79 View Post
    small hole = ?
    big hole = ?
    Sorry, but this is incorrect. Well, not entirely correct.

    Consider a 300/2.8 versus a 50/1.0. By the bighole/smallhole logic, which would be brighter? The 300/2.8 has a physical aperture of 107mm. The 50/1 has an aperture of 50mm. So the bigger hole (107mm) is brighter? No. The 50/1 is brighter in the viewfinder, and by a full 3 stops. Again, a 300/2,8 and a 50/2.8 have the same brightness, despite the huge difference in physical aperture.

    The viewfinder is brighter when the f-stop number is (numerically) smaller. This is independent of the actual physical size of the aperture.

    The f-number is a *relationship* between the external aperture and the focal length. This relationship, or ratio, determines the brightness of the image, and counter-intuitively, is independent of aperture size. A f2.8 bright lens means that every point in the output image has a brightness of f2.8, no matter if the lens is 16/2.8 or 400/2.8.

    So why is a faster lens brighter? It has to do with the amount of light (physical aperture size) per unit angle of view, which varies with focal length. A long lens, say 400mm, needs a lot of surface glass (143mm!) to collect enough light for f2.8 from a very small angle of view, while a wide angle lens, collecting light from more directions, need only 7.5mm of physical glass surface to achieve the same f2.8 brightness. This is best explained with diagrams, but i don't have one. Maybe you should just google it.

  18. #18
    Senior Member sinned79's Avatar
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    Default Re: Faster lens are brighter...BUT HOW? :O

    Quote Originally Posted by ST1100 View Post
    Sorry, but this is incorrect. Well, not entirely correct.

    Consider a 300/2.8 versus a 50/1.0. By the bighole/smallhole logic, which would be brighter? The 300/2.8 has a physical aperture of 107mm. The 50/1 has an aperture of 50mm. So the bigger hole (107mm) is brighter? No. The 50/1 is brighter in the viewfinder, and by a full 3 stops. Again, a 300/2,8 and a 50/2.8 have the same brightness, despite the huge difference in physical aperture.

    The viewfinder is brighter when the f-stop number is (numerically) smaller. This is independent of the actual physical size of the aperture.

    The f-number is a *relationship* between the external aperture and the focal length. This relationship, or ratio, determines the brightness of the image, and counter-intuitively, is independent of aperture size. A f2.8 bright lens means that every point in the output image has a brightness of f2.8, no matter if the lens is 16/2.8 or 400/2.8.

    So why is a faster lens brighter? It has to do with the amount of light (physical aperture size) per unit angle of view, which varies with focal length. A long lens, say 400mm, needs a lot of surface glass (143mm!) to collect enough light for f2.8 from a very small angle of view, while a wide angle lens, collecting light from more directions, need only 7.5mm of physical glass surface to achieve the same f2.8 brightness. This is best explained with diagrams, but i don't have one. Maybe you should just google it.
    i think at this stage i dun want to go too technical. hence i give a very brief general idea for TS to ponder.

    small hole = ? is actually to let TS thinks about it. small hole means less light and small hole means small aperture (eg f16 and above).

    big hole =? is actually to let TS thinks about it. big hole means more light and big hole means wide aperture (eg f1.2,1.4 etc).

    I wun want to bring in the focal length + aperture comparison, cos that will makes TS confuse further. So I am only talking about just aperture.
    Last edited by sinned79; 17th December 2010 at 03:10 PM.

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    Default Re: Faster lens are brighter...BUT HOW? :O

    Quote Originally Posted by sinned79 View Post
    i think at this stage i dun want to go too technical. hence i give a very brief general idea for TS to ponder.

    small hole = ? is actually to let TS thinks about it. small hole means less light and small hole means small aperture (eg f16 and above).

    big hole =? is actually to let TS thinks about it. big hole means more light and big hole means wide aperture (eg f1.2,1.4 etc).

    I wun want to bring in the focal length + aperture comparison, cos that will makes TS confuse further. So I am only talking about just aperture.
    Understood, hopefully TS starts thinking about it a little deeper on his own.

  20. #20
    Senior Member giantcanopy's Avatar
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    Default Re: Faster lens are brighter...BUT HOW? :O

    Quote Originally Posted by Jamesf View Post
    The view finder is still as bright as f/1.8 for the 50mm prime eventhough you stop down to f/5.6. It will only affect the picture you took, not the amount of light entering lens for view finder or focusing. Correct me if i'm wrong.
    yes for most of the slrs, the lens has a lever that the camera can mechanically/electronically stop down the lens aperture only while taking the photo or depressing the dof ( or the liveview i think at least for my canon )

    In that way, you get the brightest possible image from the viewfinder to ease in shooting / composition.

    Quote Originally Posted by CamInit View Post
    I don't think so. T-stops (not f-stops) for lens of different constructions are different. The number and type of lens elements will affect the amount of light reaching the view finder. Maybe not visually very significant, but it will be there.
    I think Jamesf was referring to the stop down aperture happening during the snap

    Ryan

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