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Very basic aperture question....

Discussion in 'Panasonic Cameras' started by Hugo, Oct 18, 2011.

  1. Hugo

    Hugo Mu-43 Regular

    Sep 28, 2011
    I have a very basic aperture question. It is my understanding that:

    Lower F-stop (wider aperture) = more light to come in > which allows a faster shutter speed (assuming to achieve same exposure) > which will result a shallower depth.
    On the other hand

    Higher F-stop (narrower aperture) = less light to come in > which requires a slower shutter speed (assuming to achieve the same exposure) > which will result a lager field depth.

    The following websites seems to contradict to each other….

    According to Camera Exposure: Aperture, ISO & Shutter Speed which states

    “How it Appears. A camera's aperture setting is what determines a photo's depth of field (the range of distance over which objects appear in sharp focus). Lower f-stop values correlate with a shallower depth of field:”

    According to Aperture Value and Expression*|*DIGITAL CAMERA LUMIX*|*Customer Support*|*Panasonic which states
    “A brighter lens with a large aperture (F) value has a shallower depth of field, thus producing greater blurriness.”

    Am I missing something :confused: ? And which one is correct?
  2. winx14

    winx14 Mu-43 Regular

    Dec 1, 2010
    Brooklyn, NY
    Large aperture = lower aperture number (f-stop).

    ex.- f/1.4 is a large aperture; f/16 is a small aperture

    Confused me at first also.
  3. Wasabi Bob

    Wasabi Bob Mu-43 All-Pro

    They are both saying the same thing, just using different terms.
    "Lower f-stop values correlate with a shallower depth of field." In other words, an F2 aperture = shallow depth of field.

    “A brighter lens with a large aperture (F) value has a shallower depth of field"
    By "brighter" they are referring to a "faster" lens (one that is capable of a large lens aperture (like F2). In this case "large aperture" does not mean a large "F" number <like F16>, but rather a physically large aperture, like F2.
  4. The f-stop is (or should be) expressed as ratio i.e. f/2, f/8, f/16, etc. In this case, f/2 IS a larger numerical value than f/8 (1/2 > 1/8). Often though, f-stops are expressed simply as the denominator only i.e. f2, f8, f16, etc, which is where the confusion comes from.
  5. sprinke

    sprinke Mu-43 All-Pro

    Apr 5, 2011
    Pasadena, CA
    Just want to nitpick ... the shutter speed has absolutely no relevance to the depth of field. DOF is controlled by aperture.

    However, a larger aperture does mean more light coming in and therefore a faster shutter speed can be used to collect the same amount of light that would require a longer shutter speed when using a smaller aperture.

    It all comes down to algebra, basically. Imagine that you need L amount of light in order to make a well-exposed picture.

    Assuming constant ISO in this case (which is a big assumption),

    The amount of light L = aperture (f ) x length of time the shutter is open (s)

    Let's pretend that to get your well-exposed picture you need the amount of light you would get if you used f/2 for 1/400s. In this case:

    L = f/2 x 1/400s

    Now let's say that you "stop down" your aperture to f/4. The way that apertures are designed, f/4 lets in HALF as much light than f/2. Therefore in order to keep the amount of light L constant, you must DOUBLE the shutter speed.

    L = f/4 x 1/200s
  6. scarbrd

    scarbrd Mu-43 Regular

    Jul 1, 2011
    Houston, TX
    When they refer to "larger aperture" that mean the size of the opening, not larger number. The larger the opening, the smaller the number.

    Luckypenguin is correct in how it should be stated, but it rarely is stated that way, hence the confusion.
  7. GaryAyala

    GaryAyala Mu-43 Legend

    Jan 2, 2011
    Hey Hugo, like Bob stated, they are basically saying the same thing, just using slightly different examples.

    The first stated is correct and is more of an overview for all lenses.

    The second statement is a bit more specific and is a comparison for like lenses. The second statement is stating that a fast lens with a large aperture - low f/number the more shallow the DOF over a slower lens with a smaller aperture - high f/number. This is where the confusing lies (I think).

    So let's say we are comparing two 50mm lenses, one with its widest aperture being f/1.4 and the other having its widest aperture at f/4.

    A 'fast' 50mm lens at f/1.4, f/2, f/2.8 will have significantly less DOF than the 'slower' f/4 50mm lens.

    Both lenses at f/4 and equivalent smaller apertures will have identical DOF.

    In the second statement substitute "Faster" for "Brighter" and "shallow DOF" for "blurriness".


    PS- The f number is a ratio between the focal length of the lens to the diameter of the aperture (FL/D). So a lens at F/2 the focal length is twice as long as the diameter. The f number should be written as a ratio, (in this case), f/1:2 but is abbreviated to f/2.
  8. DDBazooka

    DDBazooka Mu-43 Veteran

    Sep 3, 2011
    The thing to keep in mind is that f-stops are fractions. F/2, F/4, etc so the BIGGER the denominator the SMALLER the value.
  9. Hugo

    Hugo Mu-43 Regular

    Sep 28, 2011
    I probably shouldn't compare two different lenses but here's where I’m struggling.

    I have two lenses; a f2.5 14mm pancake and f4-5.6 45-200mm telephoto. Judging by the f stop, I’d assume that the pancake lens will generate a picture with less/narrower DOF due to the higher f-stop. However, I believe the pancake lens is better for taking landscape and architecture because it won’t bound background and objects together. Does that mean it has a wilder DOF? :confused: 
  10. DDBazooka

    DDBazooka Mu-43 Veteran

    Sep 3, 2011
    When taking landscapes/architectures you set the F/stop to a bigger number anyway (like F/16) so what the MAX f/stop is (2.5 in this case) is irrelevant.

    Just because the lens is a 14mm f/2.5 doesn't mean it has to stay at 2.5.
  11. Luke

    Luke Mu-43 Hall of Famer Subscribing Member

    Jul 30, 2010
    Milwaukee, WI
    and not to further muddy the water here, but DOF is also affected by the focal length of the lens one is using.
  12. GaryAyala

    GaryAyala Mu-43 Legend

    Jan 2, 2011
    It is tough to compare the DOF of different focal length lenses without a DOF chart, due to the differences of perspective, in this case a wide angle verses a telephoto.

    Technically speaking, I believe the 14 is a superior lens optically to the 45-200 and will deliver a higher resolution image (the higher the resolving power of the lens the greater the detail in the image). The perspective of a wide angle (14mm) is to widen the spatial gap between objects (an object behind will seem much further behind than normal) and the perspective of a telephoto (45-200) is to compress the gap between objects (a shot of multiple buildings will merge them together making them appear very close and much more densely situated than normal).

    But, (the big but), the difference in perspective is so great between the 45-200 and the 14 that I wouldn't worry about which lens to use. After you frame the shot with the 14mm, you would have to back up a considerable distance to attain a similar point-of-view with the 45mm. I would use whichever lens gave me the image I desired in my mind's eye.

    In application, the 14mm due the nature of it having a wide field of view, would be used more often for landscape and architecture that a 45-200 telephoto due to the telephotos narrow point of view.

    Remember, that Field-of-View is independent and different than Depth-of-Field. I can have a wide angle lens which has a wide Field-of-View that if shot wide open has a very shallow Depth-of-Field and by adjusting the aperture that same lens can have a very deep Depth-of-Field.

    Examples (Canon 5D with Sigma 20mm)

    Subscribe to see EXIF info for this image (if available)

    @ f/2 w/20mm

    Subscribe to see EXIF info for this image (if available)

    @ f/8 w/20mm

  13. Aniseedvan

    Aniseedvan Mu-43 Regular

    Sep 25, 2011
    An easy practical way is to line up a load of items diagonally going away from the camera, say fromle to right, front to back - beer bottles is a good one (and you have something to drink at the end!)

    Say line up 5 or 6. Focus on the middle one. Set the camera to aperture priority, take one at the smallest f number your lens will go (say f2.8) take a picture, set it to f8 take another, and take another at say f16.

    Hopefully the change in the number of bottles in focus will be sufficient for you to see what effect it has to the depth of field in that simple example.

    Then try and repeat the same experiment from twice as far away and see what the depth of field looks like.

    I have to see these things in practical terms; I hope that might help?
  14. Hugo

    Hugo Mu-43 Regular

    Sep 28, 2011
    Thank you guys. It helps a lot!!
  15. Wasabi Bob

    Wasabi Bob Mu-43 All-Pro

  16. LovinTheEP2

    LovinTheEP2 Mu-43 Top Veteran

    Feb 15, 2011
    The quoted F value of a lens is usually the maximum aperature size. So a 20mm/1.7 ... the biggest aperature is 1.7 but it can be stopped down to F4, F8 etc. Usually, the maximum aperature of a lens isn't the ideal setting for sharpness etc. Usually stopping it down 2-3 stops achieves it's sweet spot.

    For zoom lens, it depends on the lens but you can either have a Constant F zoom where the Aperature doesn't change based on telephoto setting .. or a variable which is the most common. The maximum aperature in that case is at the shortest end of the lens and the aperature gets smaller (larger f) towards the longest end. Typically, the same holds true that stepping down a bit helps with sharpness. So a 14-42mm lens, at 14mm.. step to F5.6 is usually sharper then F4.0 etc.

    IMO; based on the exposure you are trying to achieve, it's usually best to use the F-value that is the sweet spot for the lens at a given focal.. versus wide open unless you need the extra light trying to keep iso down or shutter speed above the 1/focal to keep from motion blur etc. or shallower DOF.
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