My two photography questions...

robert33823 · Oct 25, 2013

Hi everyone,

Was wondering if anyone could give me some insight into these questions:

1. How do shutter speed and aperture affect the amount and intensity of light that reaches the image sensor in a digital camera (or film in a film camera)?

2. When would you want to use a higher film speed, and what does the photographer risk by using a higher film speed?

Thanks,
Robert

rexbobcat · Oct 25, 2013

Aperture affects the actual amount of light hitting the sensor. The shutter speed affects how much time that amount of light is hitting the sensor.

And generally, the higher the film speed the more grain and less detail you get in your photos. However. High speed film allows you to use higher shutter speeds to stop action easier.

Big Mike · Oct 25, 2013

Welcome aboard Robert.

An analogy I often use for cameras & exposure, is filling a bucket of water with a hose.
The shutter is a curtain that opens and closes, the length of time that the curtain is open, is the shutter speed. Think of it as turning the water on and off with a valve. The longer the valve is open, the more water you get in the bucket. In the same way, the longer the shutter is open, the more light you allow onto the sensor.

The aperture is basically an adjustable iris (hole) in the lens. In the water analogy, think if it as using a larger hose or a smaller hose. If you use a larger hose, you will get more water into the bucket, a smaller hose would mean less water (during the same length of time). So if you use a larger aperture (lower F number) you will more light onto the sensor...and if you use a smaller aperture (higher F number) you will get less light onto the sensor.

Of course, these two things have to happen at the same time. So a larger aperture with a short (fast) shutter speed could give you the same exposure as a smaller aperture and a longer (slower) shutter speed.

The 'film speed' is the ISO. With film, it was how sensitive the film was to light. Higher number film was more sensitive and thus needed less light to make a proper exposure. That meant that with a higher ISO, you could in turn, use a smaller aperture or faster shutter speed (to get the same exposure).

With digital cameras, the ISO is basically the same, except that instead of being more sensitive to light, the ISO setting amplifies the 'signal' from the sensor. It's very much like turning up the volume on your stereo.

So there you have it. Three different settings, each has the ability to change/control the exposure of the photo. The manipulation of these three things is really the essence of what photography is.

The 'trade off' of using a fast or slow shutter speed, is how motion is captured. A fast (short) shutter speed will be more likely to freeze motion, thus you get less motion blur, thus your photo looks sharper. A slow (longer) shutter speed will allow motion (either by camera or subject) to be recorded as blur. Sometimes we want that blur, but usually it just means a less sharp looking photo.

The aperture controls the depth of field. (since you didn't ask about it specifically, I'll leave it for now).

The ISO has some consequences as well. Just like turning up the volume on your stereo will give you distortion (that you can hear)....turning up the ISO will give you distortion that you can see. We call it digital noise. It usually shows us as pixels having either tone or color that are incorrect. https://www.google.ca/search?safe=o...2.0....0...1ac.1.29.img..3.14.952.xqJgS1vUHoc

The higher the ISO, the more of that digital noise you will tend to get. There are other factors, like the design/technology of the camera, the size of the sensor, the processing etc.

So why would you ever want to use a higher ISO? Well, it comes back to the three exposure controls. By using a higher ISO, you can in turn, use a faster shutter speed which would reduce motion blur and give you a sharper photo.

limr · Oct 25, 2013

You can also shoot in lower light conditions with higher ISO.

ISO figured in much more prominently, I believe, when film cameras had more limited settings to account for different conditions. I've got a camera, for example, whose shutter speeds are 1/500, 1/250, 1/125, 1/60, 1/30, and B. In bright outdoor conditions, I can only go to f16 and 1/500 to reduce the amount of light. If I'm shooting a fast film (more sensitive to light) then my pictures are probably going to be overexposed, so it would be more important to me to have a slower film in those conditions.

These days, most digital cameras have so many more options and you still have to make a lot of choices that will effect the ultimate look of the image, but there's a lot more fine-tuning you can do. Plus, you're not 'stuck' with a certain ISO for 36 frames until the roll of film is finished. (If I were skilled at changing film mid-roll, I wouldn't be stuck either, but I can live with that

)