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Understanding F-Stops and Long Exposures

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What are long exposures? These are photographs taken through a camera’s lens while it remains open for a significantly longer period than a traditional photograph requires. For example, when someone wants to document images of star trails or the Milky Way Galaxy, they are going to be obliged to use a long exposure to get the picture.

It isn’t as easy as setting up a camera to keep its shutter open for a few minutes or even an hour, however. The photographer will also need to consider the effects of the ISO and the aperture (f/stop) that the camera is set to as well. This is because the three factors are heavily connected. When one of these settings is adjusted, it is going to affect the others. Usually if one is reduced the others must be increased.

What is f/stop then? It is the amount of light that the camera’s lens allows through to the sensor (or film). The lower the f/stop number, then the larger the aperture or opening of the lens. This also affects what is known as the depth of field, and this makes anything in the foreground or background blurry, while the main subject is in focus.

So, when we have the opening of the aperture very large, such as f/2.8, we will then need to adjust the exposure to a shorter amount to get the best results? Basically, that is going to be true.

Let’s take an example – a photographer hoping to record a good image of the night time sky. They will begin by setting up a tripod, connecting the camera and mounting a cable shutter release. This is all necessary for the best results because any sort of wiggle to the camera can cause blur and even just hitting the shutter release with the finger can ruin the entire exposure. The next thing to do is take a test shot using settings that are good for the scene, but not for the final result. For instance, someone in low light can crank the ISO as high as 3200 and the aperture as low as f/2 to get a brief exposure and instant results. This image will give a somewhat accurate representation of the final shot, but will not be of very good quality.

Using these settings, the photographer can then perform some simple math to determine the appropriate settings for the best results. This is where ISO comes into the equation. ISO was once known as “film speed” but now means the amount of sensitivity the camera sensor has to light. Optimally it should be at the lowest setting possible – 100. If we adjust the other settings to match this, we would have “halve and double” the other settings to determine the right ones. For this photo the ISO is halved five times to go from 3200 to 100. This means the shutter speed is doubled five times to accommodate the change – going from 2 to 64 seconds. If we wish to change the f/stop more maths is necessary to increase exposure time.

About the Author

Amy is an multi-award winning photographer from Australia. She teaches enthusiast photographers how to take beautiful, professional photos in easy, plain English. She has a monthly photography emagazine and ebooks to help you create stunning images every time. DigitalPhotographySuccess.com

Comments (4)

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  1. Didier says:

    With your trusty digital video camera by your side you can capture all those special moments, such as your childs first steps, your birthday or wedding, or your vacation with family and friends etc.

    With so many manufacturers and models available in the digital video market, you may find it confusing trying to choose the perfect one for you. Your choice will, however, depend on the features that you want and how much you are willing to spend.

    The most important thing t…

    Keywords:
    digital video,digital video recorder,digital video camera,digital video editing,camcorder

    Article Body:
    With your trusty digital video camera by your side you can capture all those special moments, such as your childs first steps, your birthday or wedding, or your vacation with family and friends etc.

    With so many manufacturers and models available in the digital video market, you may find it confusing trying to choose the perfect one for you. Your choice will, however, depend on the features that you want and how much you are willing to spend.

    The most important thing to consider is the format in which your videos will be stored, as the video format determines the video quality. Digital 8 otherwise called D8, MiniDV, DVD and HDD are the main types of video format that digital cameras offer. Both D8 and MiniDV are tapebased formats, with the MiniDV currently offering the highest quality video format to consumers. The DVD format allows direct video recording onto a digital disk, while the HDD type uses internal hard drives where the video is recorded. As the tape format is slowly being phased out by major manufacturers, it is a good idea to invest in disk or hard drive based digital video cameras.

    Digital video cameras also come with charged coupled device or CCD imaging sensor. Digital video cameras come with 1CCD or 3CCD features. Cameras with 1CCD suffer from poor video quality, whereas 3CCD cameras produce much better quality videos. Most professional camcorders use the 3CCD technology, thus making them more expensive than the other models.

    The optical zoom feature of the camcorder lens generally ranges from 10X to 20X. The choice of zoom depends on how close you want to get to the action. Some digital video cameras also allow still photography at various resolutions, and some camcorders offer both video and still photography features. Some digital video camcorders have inbuilt flash for lowlight photography, while some video cameras come with a Night Shot feature. Other popular options include external flashlights, external microphones and external storage devices that can be attached onto the camcorder.

    Camcorders with longer battery strength is also recommended. Digital video cameras have battery life ranging from 4 to 8 hours of continuous shooting. However, using the zoom or any external devices reduce the battery strength.

    All cameras nowadays come bundled with a digital video editing software. But if you are not satisfied with the one provided, you can always buy a better and more expensive editing software from Adobe or any other reputable brand.

    Video camera prices today vary from $500 to $4000, with Sony, JVC and Canon being the more popular brands.

  2. Bob Johnson says:

    A great piece – thank you so much for posting it. I would definitely recommend thet every one else should have a look at it.

  3. Mariel says:

    It’s always nice to brush up on the basics of digital SLRs. I’m always trying to improve my photography skills so that I can make my personal blog even better! It’s nice to have sites like this to come to for great information. Keep it up, you’re helping lots of people!

  4. George says:

    Marc….Did you not write the same reply to the colour wheel article…Try to be a bit less boring please.

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