A&P shutter speed, exposure, ISO

Discussion in 'Lifestyle' started by ChosenGSR, Jul 18, 2003.

  1. ChosenGSR

    ChosenGSR Mama always said you'd be the chosen one

    Joined:
    Oct 24, 2001
    Messages:
    51,099
    Likes Received:
    241
    Location:
    HoCo, MD
    I just recieved my canon s400, looks like exactly what I wanted... anyway I am pretty much a noob when it comes to photography. I've been using a kodak easy share 4230 before, strictly point and shoot with no settings at all.

    My question is what exactly does shutter speed, exposure, and ISO do ? I understand that atleast the first 2 have to do with lighting... From what I understand ISO speed allows to take pictures of moving objects with less blur ?

    also, at what situations would I want to use these features.

    Thanks in advance :wavey:
     
  2. Jcolman

    Jcolman OT Supporter

    Joined:
    Aug 19, 2002
    Messages:
    43,133
    Likes Received:
    90
    Location:
    east coast
    Following is a quick primer for using aperture settings, shutter speeds and film speeds. For for information I recommend the book "The 35mm photographers handbook"


    Shutter speed refers to how long the camera shutter stays open, allowing light from the lens to fall on the film. A fast shutter speed (1/500 of a second or faster) is good for "freezing" action. A slow shutter (1/60 of a second or slower) requires the use of a tripod otherwise you'll end up with a blurry photo, especially if your using a long lens.

    Aperture refers to the lens opening that admits light to the camera. The aperture is marked with numbers, called f/stops, that usually read like this: f/2.4 f/4 f/5.6 f/8 f/11 f/16 f/22. The lower the number (f/2.4) admits more light while f/22 admits less light. Additionally, a smaller aperture like f/22 gives you more "depth of field" or overall sharpeness from near focus to infinity. The important thing to know is that f/stops and shutter speeds are designed to send exactly twice as much light to the film with each increment. In other words, a shutter speed of 1/250 of a second will send twice as much light to the film as a shutter speed of 1/500 of a second. Conversely, a lens opening of f/4 will send twice as much light to the film as a lens opening of f/5.6. This means that as you change shutter speed from 1/250 to 1/500 you must also open your lens aperture one f/stop to maintain the same exposure value.

    Determing the exposure value is the job of the light meter. All modern cameras have a built in meter. The meter measures how much light is coming in the lens to give you the proper shutter speed to use in any given light. The meter must also know the film speed (see below) that you are using. Most modern cameras do this automatically, however some cameras must have this step performed manually.

    ISO refers to the films sensitivity to light. The "faster" or higher ISO or ASA number on the film, the more sensitive to light. A higher speed film means that you can take photos in dimmer light conditions. However, the faster the film, the more "grain" in the negative. This means that a print made from a high speed film negative won't appear as sharp. The rule of thumb for chosing film speed is to use the slowest (lower number) film for your expected light conditions. You can use film with a rating of 64 for all daylight exteriors as long as you use a tripod and slower shutter speeds or wider apertures. Most popular films today are rated between 64-800. Use 400-800 speed film for low light levels.

    Anyway, I hope this helps get you started. Good luck and post some photos.

    Cheers
    Jim
     
  3. ChosenGSR

    ChosenGSR Mama always said you'd be the chosen one

    Joined:
    Oct 24, 2001
    Messages:
    51,099
    Likes Received:
    241
    Location:
    HoCo, MD
    yes, that somewhat helped... although I was talking about a digital camera, so the notion of film doesnt exist ?
     
  4. Jcolman

    Jcolman OT Supporter

    Joined:
    Aug 19, 2002
    Messages:
    43,133
    Likes Received:
    90
    Location:
    east coast
    Well yes it does in a way. Think of the camera as using only one film speed. That is the sensativity of the camera. The beauty of film cameras is that you can change film for different conditions, but your digital camera only has one sensativity. Now, since I don't use digital cameras I'm partial to film cameras. If anyone else uses digital cameras please correct me if I'm wrong.

    Let me give you an example of using the correct shutter speed coupled with the correct f/stop or aperture.

    Lets say you're going to take a picture of a car and the car is parked. Your camera's meter gives you a reading and it sets the shutter speed to 1/60 of a sec. at f/16. You are using a telephoto lens and the camera is on a tripod. You take a photo and being digital, you look at the photo instantly. You don't like the fact that the background behind the car is too sharp. On the next photo, you open the lens to f/4 so as to reduce the depth of field. In order to maintain the same relative exposure value (correct exposure) you must use a faster shutter speed since you're letting more light hit the film (or chip in your case). Since you opened your lens four stops (f/4 f/5.6 f/8 f/11 f/16) from your original setting you must set your shutter speed to 1/1000 of a second (1/60 1/125 1/250/ 1/500 1/1000) to decrease the time that light hits the film. This combination of 1/1000 @ f/4 will give you the same exposure as 1/60 @ f/16. The only difference is now you have less depth of field, or overall sharpness. Additionally, if the car was in motion racing down a track, you could use the faster shutter speed of 1/1000 to "freeze" the action and obtain a sharp picture while the car was moving.

    Cheers
    Jim
     
  5. mojito

    mojito New Member

    Joined:
    Mar 8, 2003
    Messages:
    62,877
    Likes Received:
    0
    You can change the iso of a digital camera. Don't kow which levels you're given on that particular model, but my D30 allows between 100-1600. That means that under bright condition I'll have it at 100-200 for the sharpest pictures since there plenty of available light. For most days here in the Pac NW under gray skys, I'll have it at 400, so that I can stillget an extra F-stop out of the available light. For night pictures, I might go to 800 or 1600 to try and get the shot, though you'll see a lot noise (digital equilavent of grain) in the picture.

    so if you were shooting iso-100 and had f/8 @ 1/60 and needed a faster shutter speed, you could either stop it down, to 5/5.6 or lower, which will slightly alter depth of field, or you could move the iso up, to 200 or 400 and then be able to hand hold the camera with decent success and a sharp picture.
     
  6. Jcolman

    Jcolman OT Supporter

    Joined:
    Aug 19, 2002
    Messages:
    43,133
    Likes Received:
    90
    Location:
    east coast
    I didn't know that. Thanks for the clairfication.

    What you mean is that you would open the aperture to f/5.6 not stop it down. Stopping down means to close the aperture to a smaller f/stop (which means a larger f/number i.e. f/8 is a smaller aperture than f/5.6)). Don't mean to jump your post, just trying to not to confuse others.

    Jim
     
  7. UncleMeat

    UncleMeat Guest

    I've noticed even on some of the more "point and shoot" like digitals, they are starting to have adjustable ISO. Even on the $200-300 models. Isn't technology grand? :)
     
  8. mojito

    mojito New Member

    Joined:
    Mar 8, 2003
    Messages:
    62,877
    Likes Received:
    0
    woops, hadn't had any coffee yet this morning
     
  9. Joe

    Joe 2015 :x: OT Supporter

    Joined:
    Apr 29, 2002
    Messages:
    116,622
    Likes Received:
    1
    Location:
    nocal
    jim said almost everything i want to say...

    just to clarify.. digital cameras will allow you to change isos.. instead of a change in grain size, you'll get what's called "noise" a quick search on google for a better definition turned up this site which explains it pretty well... http://www.binbooks.com/books/photo/i/l/541E6AF80D

    also, alot of newer cameras have easy to use bracketing... (the little +/- dial on the camera)

    what i taught my kids (did one of them jr high outreach things) was to take their cameras, pick one object, get a tripod and shoot the exact same thing... shoot a few with various fstops and find the right shutter speed for it... then start at f8, meter for the right shutter speed, then try bracketing 3 stops in each direction in half stops...

    letting them see the slides and seeing the difference between a park shot at f22 and f4 (depth of field) and somethign that's metered right and something that's one stop over exposed and one stop underexposed helped them learn so i figure it might help you too...
     

Share This Page