what is the difference between shutter speed and ISO?

Question by katanini: what is the difference between shutter speed and ISO?
and also, what is shutter speed shown in?
i want to know because i have a canon power shot and i want to know how to increase shutter speed to reduce motion blur without increasing ISO, which makes pictures noisy.

Best answer:

Answer by fhotoace
Shutter speeds are measured in from seconds to fractions of a second.

ISO is the measured sensitivity of the film or sensor

Blur is caused by camera movement.

Shooting at shutter speeds of at least 1/250th of a second can reduce noticalbe blur

Since the shutter speed is dependent upon the amount of light falling on the subject, adjusting the ISO is sometimes the only way to produce a high enough shutter speed in low light conditions

You have a choice. You can either have image blur or you can have image noise. Sure you can spend $ 5,000 on a Nikon D3 and get amazing low noise at high ISO shots, but you will have to learn how to use the fully adjustable camera to do that (and of course spend the big bucks)

What do you think? Answer below!

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2 Responses to what is the difference between shutter speed and ISO?

  1. FritoLay says:

    Shutter speed -> Measured in time
    ISO -> Measured in imaginary brightness boosting, noise inducing, electronic stuff. (As gateway pointed out, this is technically not really what ISO is.)
    Aperture -> That other thing that controls the volume of light that passes through the lens.

    You would have to increase the aperture opening (smaller f/#) to decrease the ISO and increase the shutter speed. Which is just dazzling, because I’m guessing your camera is already fully opened (referring to the aperture), since cameras normally automatically do that before they increase the ISO. This is (partly) why people buy super duper expensive lenses with large apertures.

    PS: Straight from the D40 manual (page 37):
    “ISO sensitivity is the digital equivalent of film speed.” ISO sensitivity is a digital/electronic thing then right? Right.

    But seriously though, haha, you’re technically right as I have film with ISO ratings on them. I just had to find a way to bend my argument… where better to look than a user manual for a digital camera? =)

  2. gatewaycityca says:

    ISO is a standardized unit of light sensitivity, and it applies to both film and the sensor in a digital camera. A higher ISO number means more light sensitivity, and a lower ISO number means lower light sensitivity.

    By the way, ISO is not some “imaginary, brightness boosting, electronic stuff”…it’s an international unit of light sensitivity and it existed LONG before there were digital cameras. It started with ISO ratings on film. And before that, there was another rating called ASA.


    With a film camera, the ISO rating is sometimes called the “film speed” (although that isn’t really a good term to use). A film with a higher ISO rating would be more light sensitive. So 400 ISO film is more sensitive than 200 ISO film.

    With a digital camera, you can adjust the sensor’s light sensitivity. You can turn up the sensitivity by increasing by ISO setting, but like you said the drawback is that it will generate more noise in the picture. So you should keep the ISO as low as possible.

    The shutter speed determines how long the shutter stays open when you press the button. It applies to both film cameras and digital cameras. It’s usually measured in fractions of a second, like 1/100 for example. But on some cameras, you can also do long exposures, like several seconds, several minutes, or even up to several hours on some cameras.

    The overall exposure of a picture depends on the ISO rating (how sensitive the sensor or film is), the shutter speed, and the aperture. If you want to use a low ISO, and with a fast shutter speed, then you will need to use a bigger aperture (by using a different F-stop setting).

    Here’s the other catch. If you change the aperture, it will affect the depth of field. With a wider aperture, you will have a more shallow depth of field and the background will start to look blurry.

    So you will have to find a compromise between ISO, shutter speed, and depth of field.

    Also, I don’t know about your particular camera, but if all you have is a digital point and shoot camera then you might not even be able to change the F-stop manually. Most digital point and shoot cameras are completely auto exposure and you have very little control. To have total control over the exposure, you would either need a manual film camera (35mm rangefinder or SLR) or a digital SLR camera.

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