f / stop confusion

Discussion in 'Photography Beginners' Forum' started by Captain Ahab, Jun 27, 2007.

  1. Captain Ahab

    Captain Ahab TPF Noob!

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    I have been studying and I am learning quite a bit (still don't have my camera yet-but in no hurry) I know some of this will come to me when I finally do start really taking shots - I understand the f-stop or aperture for allowing light, and also for depth of field- but when you go shopping for lenses they may say 2.8-5.8 (or something there abouts) what is that telling me? Is that the only stops I will be able to use even though the camera itself will have more of a range? I am probably waaaaay off here. Help me out a little. Thanks in advance.
     
  2. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    The description of the lens lists the MAXIMUM aperture of the lens. So if it is a 50mm F1.8...the maximum aperture is F1.8. The minimum aperture is something like F22 or F29...and isn't really important.

    When they say something like F3.5-5.6...that means that there is a range of maximum aperture. The range will follow the zoom of the lens. For example, with the EF-S 18-55mm F3.5-5.6 lens...the max aperture at 18mm is F3.5 and the maximum aperture at 55mm is F5.6.
     
  3. jeremyboycool

    jeremyboycool TPF Noob!

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    Now I am confused! :lol:

    How does aperture affect the picture?
     
  4. deanimator

    deanimator TPF Noob!

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    There are 2 things which control how much light hits the film/sensor
    1) aperture = the size of the hole
    2) Shutter speed = how long the hole can be open
     
  5. Soocom1

    Soocom1 TPF Noob!

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    Ok.
    As you know, the f-stop involves the amount of light coming in.
    Now. The smaller the number..(1.2, 1.7, etc) the larger the hole. This is a narrow depth of field, and only what is directly focused on will come out in focus. In addition, the larger aperture means that the shutter can be set to a faster setting with a given ISO setting. (A setting of 1/125th at an f 1.8 with an ISO of 200, vs. a setting of 1/60th at an f 2.3 also at ISO 200). Thus, a 'faster lens'.

    Now if you have for the sake of argument the lens set at f22, that means that anything the camera is focused on as well as everything behind the subject will also be in focus as well. This allows for tremendous depth of field. There is actually groups that are devoted to f32. (mostly large format crazies like myself). But they shoot almost exclusively f22 and higher. This is also a situation mostly for landscape purposes.
     
  6. jeremyboycool

    jeremyboycool TPF Noob!

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    Thanks for clearing it up guy!

    How do I tell the the min f # that a lens supports?
     
  7. Digital Matt

    Digital Matt alter ego: Analog Matt

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    It is usually written in the description of the lens, for example.

    Canon EF 50mm f/1.8

    If it is a zoom lens with a variable maximum aperture, then it will read something like:

    Sigma 70-300mm f/4~5.6

    This means at 70mm, the max is f/4, and at 300mm, the max is 5.6. As you zoom, the max aperture gradually scales down to 5.6
     
  8. jeremyboycool

    jeremyboycool TPF Noob!

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    Thanks, Digital Matt!

    Let me see if I got this straight.

    Canon EF 50mm f/1.8

    The EF is the mount?
    50 mm is the foucal length?
    f/1.8 is the max aperture?

    But I need a large f # for landscape right? Like f/13? So how do I determine that?

    Sorry for all the questions, I did try reading up on it on the internet but got lost with all the technical terms.
     
  9. deanimator

    deanimator TPF Noob!

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    There´s no "rule" that says you must do this or that.

    Important to know is : the smaller the aperture = the more Depth of Field

    DOF is how much of the view is sharp...in focus

    Think about this:
    20mm lens. Set f 22. Set focus at say 8m. Everything is in focus from 1m to infinity.
    200mm lens. Set f 4. Set focus at 8m. Only stuff between 7.5 and 8.5m is in focus.

    Depends what you are are shooting...it´s possible to create wonderful landscapes in either situation.
    The traditional thinking is: landscapes look best with a long DOF...that is, they look sharp from near the camera to far.

    How much DOF you set up is your decision...and you have to think about the exposure and the type of lens you are using...and the effect you want.
     
  10. Digital Matt

    Digital Matt alter ego: Analog Matt

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    Aperture can be a confusing subject, but if you think of it as opposite, it will make sense. A large aperture has a small f#. F/1.4 is very large, or "wide". The actual opening of the aperture opens very wide. F/22, while the number is larger, is actually a very small aperture. The hole closes down very small.

    The minimum aperture of a lens is not given in the description. Most modern lenses go to at least f/22, while some macro lenses will go to f/32 or even f/64.
     
  11. jeremyboycool

    jeremyboycool TPF Noob!

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    Thanks for explaining it, deanimator and Digital Matt!

    It is starting to make senses now. Never realized how technical photography is.
     
  12. Mad_Gnome

    Mad_Gnome TPF Noob!

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    I like to think of exposure like a math equation. I think very technically by nature, so it makes sense to me. And photography is only technical in the sense of the equipment specs. Once you learn how to use them to create the image you want, you've moved beyond technical into artistic. The technical stuff takes up a much smaller portion of photography than the artistic, trust me.

    Understanding aperture, ISO and shutter speeds will come a lot faster once you pick up the camera and start experimenting. All of it can make some amount of sense in explanation, but once you change a setting in-camera and SEE what happens, you'll have an "AAAAHHH! NOW I get it!" reaction. That's how I've learned half of what I know: simple experimentation.
     

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