Newbie: Aperture v. Shutter Speed

[drguitarum2005]

I am brand new to photography other than your occasional disposable camera shots. Ive been workin on the whole idea of aperture and shutter speed but there are a few things I don't quite understand. If I am shooting a shot in medium light (indoor light) and I want to open the aperture all the way (smallest f number, i htink it was f2.8) and also use a high shutter speed (1200), how come the picture is dark? What is the relation between the two that makes it dark and that when not in manual mode, when you open the aperture, it lowers the shutter speed and vice versa? Thanks.

[ohenry]

It's dark because it is underexposed. Cameras require the proper amount of light to expose the CCD/film.

http://www.photo.net/learn/making-photographs/exposure

http://www.luminous-landscape.com/tutorials/understanding-series/understandexposure.shtml

[drguitarum2005]

alright ive been reading those things but i still have a basic question to ask:
with the aperture as wide as itll go (2.8 in my case), it hsould be letting in maximum light, but with a fast shutter speed, is it as if the shutter going that fast is not allowing enough light to hit the CCD or what?

[ejwebb]

Just because the aperture is open as wide as it will go does not mean there is enough light for a proper exposure. The length of time the shutter is open also determines how much light hits the sensor. The longer the shutter is open the more light hits the sensor.

If I am shooting in the house at night with normal lights I regularly need an aperture of f/1.8, ISO 400 and shutter speed of 1/30 of a second to get proper exposure. For each "stop" change you double or halve the amount of light. If I were to change any one of those variables I would have to make an opposite change in one of the others. For instance, if I moved the aperture up to 3.6, I would have to either move ISO up to 800 or shutter speed down to 1/15 of a second to maintain proper exposure.

Hope this helps.

[drguitarum2005]

ah, yes it does, thanks. I guess its pretty logical really, if you have the shutter open longer, more photons can get through to the CCD, and aperture is just a second mechanism for controlling the light coming through.

[cmM]

even though you have the lens wide open, 1/1200 of a second is not enough time to expose properly. That's where your built in light meter is handy, it tells you how to expose correctly. Also, use the histogram. It helps a lot.