stop down

[pixiegirl]

I have very very beginner questions... about terminology. If someone says take a pix at f/16 and open up the aperture that means say take it at f/11 (or f/8, that direction) correct?

What does the term stopping down mean, going the other way? Is "open up" and "stop down" sort of like opposites?

What do you say when your shutter speed goes from say 1/125 to 1/250? is there a term for that?

Thanks, you have to start somewhere!

[ianpinion]

Hello pixiegirl and welcome to the forum.

First things first, a stop is a unit of exposure or a measurement of light. When you adjust either the size of the aperture or the length of time the shutter is to open this is measured in stops of light.

You will notice that when you're shooting in Aperture Priority Mode and you go to adjust the size of the aperture, each click of the control wheel is the equivalent to a third of one stop. So every three clicks of that wheel will adjust the aperture by one stop. Likewise, when you do this, you will also see the shutterspeed change by the same amount in the opposite direction to balance the exposure, because your camera will decide how much light needs to pass through the lens and on to the sensor to correctly expose the image. This is a set amount, so by opening the aperture wider you let more light into the lens and it takes a shorter length of time for that amount of light to hit the sensor.

The other influence on exposure is the sensitivity of the sensor itself. This is termed the ISO. ISO is also measured in stops of light and again it is calibrated in third of a stop incriments. So again every third incriment you click to will be one stop higher or lower than where you started from.

I hope that is now a little clearer for you. The next step is understanding whatelse happens when you decide to open up the aperture from a very small hole to a very large hole!

[pixiegirl]

ok it was your last line I think that answers my question! I "think" I get generally, how exposure works, its just the terminology that confuses me.

My aperture... if it has a smaller number is open wider and has a shallow depth of field.... right? And if it has a "higher" number ( I guess they are really fractions so in reality and mathematics its not really a bigger number but I don't want to make it more confusing then it already is!) then it has a longer depth of field and the hole in the aperture is small.

But it was more how to use the terminology: Lets say I take a meter reading and the aperture reading is f/2 and for whatever reason I decide to take the pix at f/4 do I say I stopped it down to f/4?

[ianpinion]

You're correct that both aperture values and shutterspeed values are expressed as fractions. The term stopping down, simply describes that you're trying to lessen the amount of light reaching the sensor to prevent it from over-exposing the image. You might want to do this because the highlights in the image are too bright, causing you to lose all the detail in them. This is because a camera can only handle a limited range of light values from light to dark, so anything above or below it's range is 'clipped'. Highlights that are out of it's range are termed as 'blown highlights' and photographers will often adjust their camera's settings so they just avoid 'clipping the highlights. The same goes for the opposite end of the scale with shadows.

This is why you will see a large number of landscapes are shot as HDR (High Dynamic Range) where photographers take a series of photographs of the same scene to capture all the light values from the highlights to the shadows and blend them together.

[chris-p]

Ian has basically summed it up for you here, so it's mostly redundant when I say "come and have a look at the tutorials on my website..."