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Thread: Qns regarding len's f-stop

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    Default Qns regarding len's f-stop

    lets say a len is f2.8. Does it means this len will always operate at f2.8? Only way to change the amount of light is through the camera's aperature and exposure?

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    When mounted (presumably on a Nikon/Canon body) the aperture will be opened to f/2.8. Based on the selection on the camera body, when the shutter is released, the aperture will be released to the selected value.

  3. #3

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    Quote Originally Posted by espn
    When mounted (presumably on a Nikon/Canon body) the aperture will be opened to f/2.8. Based on the selection on the camera body, when the shutter is released, the aperture will be released to the selected value.
    err.....i dont understand....

  4. #4

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    i think you're talking about some lens like say err... 28-70mm f2.8 smthing like that isit? If it is, then answering your question, the largest aperture is f2.8. Most 35mm SLR lenses will be able to reach f22.
    When i was a newbie i thought abt this qn too. (maybe it's only me) but for all 35mm lenses the f-stop nomenclature (name) is just the largest aperture size of the lens.

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    When mounted (presumably on a Nikon/Canon body) the aperture will be opened to f/2.8. Based on the selection on the camera body, when the shutter is released, the aperture will be released to the selected value.
    yep... if you dial in the aperture at 2.8 on your camera it'll be at 2.8, if f/4 then it'll be 4... then 5.6 etc... smaller the aperture the slower the shutter speed to compensate for the exposure.

    Shooting at the widest aperture - f/2.8 (presuming ur lens is a f/2.8) will allow a lot of light in, so you can shoot at higher shutter speeds. When your aperture is smaller (bigger number) you'll have to slow down the shutter to let more light hit the sensor - the smaller the aperture the less light is allowed through the lens.
    Last edited by ParkertR; 9th March 2005 at 10:53 PM.
    Budget wedding photographer :)

  6. #6

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    Quote Originally Posted by kensh09
    lets say a len is f2.8. Does it means this len will always operate at f2.8? Only way to change the amount of light is through the camera's aperature and exposure?
    okie.. to answer ur queries.. with a lens with aperture rated as f2.8.. it simply means the biggest aperture is f2.8...for lens that have aperture rated f3.5-4.5... it means that, at the wide angle end, its f3.5 biggest but it will gradually be smaller to f4.5 to the tele end.. the camera does not always opeerate at the max aperture.. u input the aperture size in case of Av or A mode..in e case of the TV or S mode.. the camera will then select an apporiate aperture to match the selected shutter speed to get a balanced exposure..

    (but for the case of the nikon 60mm micro.. its rated as a f2.8 lens.. but at the marco range.. the max aperture will drop to ard 3.5 or thereabts...I'm not sure abt the others, thats just based on my own experience)

    when u dial in the aperture setting in the camera.. u are actually changing the size of the aperture.. in the old days of manual camera.. u have to manually adjust the lens aperture on the lens itself...with the amount of electronics.. we can then do the adjustments via the camera..

    when u set a particular aperture.. it will not reflect in the viewfinder... u have to depress the DOF button to actually see the difference..

    advantages of a f2.8 lens.. to many its the bokeh.. to some, its the focusing speed.. wat do i mean.. since f2.8 is bigger then f3.5 in size.. it simply allows more light.. this will affect af speed too.. bigger aperture also allows us the benefit of shooting in low light.. by using a bigger aperture.. we can gain shutter speed which sometimes, its a difference of getting a sharp pic or enough speed to freeze an action..

    anyway, hope I have managed to answer ur question

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    Quote Originally Posted by kensh09
    lets say a len is f2.8. Does it means this len will always operate at f2.8? Only way to change the amount of light is through the camera's aperature and exposure?
    Almost all lenses have an range of aperture within which they operate. The number stated on the exterior of the lens (e.g. f2.8) is typically the maximum size aperture for that lens. The typical minimum aperture sie is from f22 to f32.

    For most modern automatic SLR bodies, you will dial in an aperture setting on the body. The body will then communicate this information to the lens. However, the lens DOES NOT close down to the set aperture until you PRESS the shutter. For instance, you set f8 on the body, and look through the lens, but the view through the lens hasn't dimmed because the lens is still at f2.8. The camera does this to maximise the amount of light coming through the lens for focussing, metering and for the viewfinder. When you press the DOF button, now you can see the view dim noticeably, 'coz the lens has closed down to the set aperture. When you press the shutter release button, a few things happen; the lens closes down to the set aperture, the mirror flips up, the shutter opens....and voila.....light hits the sensor/film.

    Cheers,

  8. #8

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    Oic.....thanks all for your kind help...
    1 more qns.....What does the 'G' stands for, e.g Nikon's AF70-300G or 'ED' for some lenses?

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    Quote Originally Posted by kensh09
    'ED' for some lenses?
    Erectile Dysfunction? Another word for a soft lens I guess.....

  10. #10

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    Quote Originally Posted by kensh09
    Oic.....thanks all for your kind help...
    1 more qns.....What does the 'G' stands for, e.g Nikon's AF70-300G or 'ED' for some lenses?

    G in Nikon Stands does not stand for anything except it is the letter after F .... but G lens in Nikon are the ones without aperture ring, thus would not work with manual cameras like other non-G lens

    ED standard for "Extra-low Dispersion" a technology to help eliminate secondary chromatic aberration

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    Quote Originally Posted by kensh09
    Oic.....thanks all for your kind help...
    1 more qns.....What does the 'G' stands for, e.g Nikon's AF70-300G or 'ED' for some lenses?
    Nikon uses the designation "G" for lenses that do not have the aperture ring on them. Lenses like the 18-70mm, 70-300mm or 24-120mm are built as such.

    ED is used to designate lenses that contain glass that promotes "Extra low Dispersion" Let me see if i can explain this as simply as possible:

    Light travels into the lens. The glass in the lens focuses the various colours on a line. If you put a source of light through a prism, you'll see the dispersion of light which is also the spectrum of light ROYGBIV. Dispersion is the cause of Chromatic Abberation, which is in turn caused by the different wavelengths of ROYGBIV (hence ROYGBIV all focus at different spots). Zoom lenses are affected more, and are thus harder to produce than prime lenses because of this phenomenon. So, to minimize dispersion (and the resulting chromatic abberation), manufacturers have started inserting glass to "force" the spectrum of RGB to focus as close as possible. Hence you now get lenses that advertise APOChromatic (three lens elements to achieve the same focal length for three wavelengths-RGB) properties etc.

    I think i got this right. Anyone care to read through?

  12. #12

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    Quote Originally Posted by Reflection
    manufacturers have started inserting glass to "force" the spectrum of RGB to focus as close as possible.
    ED elements dun actually "force", its more like when light passing through a "denser" medium causes the dispersion. So its more like deterring as the ED is a better medium for the light. Its mostly flourite based and extremely brittle thus hard to manufacture. Therefore, its price. May it be L in Canon, APO in Sigma/Minolta, ED in Nikon, they are pretty much the same.

  13. #13

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    Quote Originally Posted by tan131
    advantages of a f2.8 lens.. to many its the bokeh..
    Bokeh is the term to describe the rendering of out of focus area, I think it has nothing to do with f/stop of the lens. A 50 mm at f/1.4 may or may not produce a better bokeh than a 105mm at f/2. Personally I felt that this is a rather subjective term since as far as I know there isn't a way to quantify good bokeh. Its always a "relative" comparison of this lens' bokeh is more "pleasing" than the other.

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    Quote Originally Posted by litefoot
    ED elements dun actually "force", its more like when light passing through a "denser" medium causes the dispersion. So its more like deterring as the ED is a better medium for the light. Its mostly flourite based and extremely brittle thus hard to manufacture. Therefore, its price. May it be L in Canon, APO in Sigma/Minolta, ED in Nikon, they are pretty much the same.
    My apologies for the lack of a better word.

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