This past weekend I went to a show with my friend, who was competing, so that I could take pictures of her. When I got there I found out the classes were being held in an indoor arena. I love my camera (it is a NikonD40X), but as soon as it begins to become even a little bit dark, the pictures turn out very blurry. So, of course, almost all of the pictures I took in the indoor were crap. If I use the flash, my camera can take very crisp pictures in the dark, but I did not want to turn the flash on because I was afraid it would be inappropriate and scare the horses.
Does anyone have any suggestions?
When shooting in low light there are three things you're going to want to look at on your camera/lens.
1) What is your maximum aperture?
2) What is the maximum USABLE ISO?
3) What is the minimum shutter speed to ensure non-blurry/soft pictures.
Lets talk about apertures first.
In a digital camera the aperture basically controls the amount light that reaches the sensor. In a film camera it controls the amount of light that reaches the film. (Aperture is also a major factor in depth of field, but that's not too important right now.)
Aperture is usually referred to in "F-stops". An f-stop is basically a factor, it is the ratio between the diameter of the aperture in the lens and the focal length of the lens. The smaller the f # the LARGER the opening, the more light you get in, the faster your shutter speed can be. The larger the f # the SMALLER the opening the less light you get in, the slower your shutter speed has to be. Your lens will have the max aperture printed on it.
Your lens is what determines how large or small your aperture can be. Since you have an SLR you can change lenses. If you have a point and shoot, you can't. A common lower priced zoom is the 70-300 f/4-5.6. This means it is not a fixed aperture; that zoomed out to 70mm you can have a max aperture of f/4; zoomed in to 300mm you can only get a max aperture of f/5.6. More confusing than you have to know right now is that the difference between f/4 and f/5.6 is one whole stop. This means that at 300mm you're only getting half of the light to the sensor that you could get in the same about of time at 70mm.
Lenses with large max apertures are called fast lenses because they allow for faster shutter speeds.
So, you want that largest aperture possible (smalled f #) so that you can have the fastest shutter speed and lowest ISO.
Now, what is ISO?
ISO in your digital camera tells you how sensitive your camera's sensor is to light. In film cameras the film is what had the ISO (or ASA) rating and this was commonly called "speed". But, a more correct definition is "sensitivity". The higher the ISO rating the more sensitive your camera is too light. Most SLRs have a low ISO setting of 100 or 200. Most SLRs have a high ISO rating of 1600, 3200, or 6400. It's rare in consumer or prosumer cameras to find usable ISO of 3200 or 6400 as you just get too much noise. ISO 1600 is quite usable from most cameras IF the image is properly exposed.
You want to use the lowest ISO needed, but upping the ISO and getting a well exposed shot is better than have lower ISO and an underexposed shot.
Shutter Speed
The shutter speed determines how long the shutter stays open and consequently how much light hits the sensor. Longer shutter speeds allow more light. Shorter (faster) shutter speeds allow in less light. Unless you're using a tripod and/or shooting stationary objects you'll want to use faster shutter speeds as you'll want to "stop motion" and prevent motion blur.
If you take a picture and the horse is blurry but the background is in focus you are holding your camera steady, but the horse is moving too fast for the shutter speed you've set. If your whole image is blurry either you didn't focus correctly or you moved your hand while taking the picture. Shutter speeds like aperture and ISO increase and decrease by halves or doubles.
So, using the 70-300 mm f/4-5.6 lens in an example if a properly exposed shot with your camera and lens was a shutter speed of 1/500 and an aperture of f/4 @ 70mm when you zoom in to 300mm your lens will automatically stop down to f/5.6 and you'll have to slow your shutter speed down by half, to 1/250.
Additional Stuff
I prefer fast lenses with a max aperture of 2.8 or larger. However, these are generally large and expensive. You'll have a difficult time in most private indoors with anything slower than that.
To stop action for horses I prefer the fastest shutter speed possible for lighting conditions. In an indoor this could mean 1/320 (I wouldn't go slower or I'd risk motion blur.)
