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How can I do Over- and Underexposure? What says me the F/Stop? If I would meter a scene at F/5.6 at 1/125. The Normalexposure would be F/5.6. What would be the 1 F/Stop by Over- and Underexposure? i cant understand this. When you can't answer me this question, please tell me a website where I can find things like this! Thank You

Mari

-- Marielle Otto (Marielle1029@aol.com), February 08, 2001

Answers

There are a few basics you need to know: 1. The F stop is calculated by taking the focal length of the lens (the distance from the lens to the film) and dividing it by the working diameter of the lens. The focal length is printed on the front of your lens. It's stated in millimeters. 2. For a fixed focal length lens (i.e., not a zoom lens), the focal length is a constant. The "standard" lens for most 35mm cameras has a focal length of around 50 millimeters. The working diameter of the lens is changed when you open or close the lens diaphragm (when you open up or stop down the lens). 3. If you have the lens diaphragm set so the working diameter is 12.5 millimeters, then the F stop is 50/12.5 = f4. 4. When you move from one F stop to the next, you are either doubling or halving the exposure. f5.6 is half the exposure of f4 and f2.8 is twice the exposure of f4. So in your example, if the light meter gives you a reading of f5.6 at 1/125 sec, you will get one stop overexposure if you manually set the lens aperture at f4 and you will get one stop underexposure if you manually set the lens aperture at f8. 5. I would recommend an introductory book on photography from your local bookstore; it would be far easier than trying to surf the web for this type of information. Good luck.

-- Larry Rudy (ljrgcr@cetlink.net), February 08, 2001.

Mari, The easy answer is if your normal setting is as you say 1/125th @ f5.6, under exposure would be 1/250th @ 5.6 and over would be 1/60th @ f5.6. You can do the same thing with your f stop instead of shutter speeds. It would look like this: with 1/125th @ f5.6 being your normal exposure... 1/125th @ f4 would be 1 stop over and 1/125th @ f8 is one stop under exposure. Every time you change your shutter speed higher, your halfing the amount of light thereby under exposing... and when you slow your shutter speed, i.e. going to 1/60th, your doubling your light. Not wanting to get to technical and confusing you more (I know it can be very confusing at first), Kodak has some pretty good books on Basic Photography and should be able to be found at your library. Cheers

-- Scott Walton (f64sw@hotmail.com), February 09, 2001.

With no change in shutter speed: A smaller f/ number gives less exposure.

A larger f/ number gives more exposure.

F/ numbers are fractions, and so a bigger number means smaller portion. (1/2 is more than 1/4, so f/2 is more light than f/4.)

-- Charlie Strack (charlie_strack@sti.com), February 09, 2001.


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