Nikon and Canon 50mm f1.8 Prime Lens

For around $100, you can buy a great lens for low light situations. It's a 50mm f1.8 prime lens and is available for both Nikon and Canon.

The 1.8 maximum aperture allows a ton of light to get to your digital sensor and makes it possible to get a good exposure for low light sitations such as dawn, dusk, and indoors. The aperture is essentially the hole in your lens. Think of the number like a fraction, so 1.8 is like 1/1.8. The smaller the number on the bottom of the fraction, the larger it is. For example, if you have a 28-70mm f4-5.6 lens, the biggest your aperture can get is f4 at 28mm and f5.6 at 70mm. F1.8 allows in more than double the amount of light than F4.

There is a side effect of having a large aperture, which is the depth of field. The larger the aperture (the lower the number), the more narrow your depth of field is. Depth of field is how much of the picture is blurry from the point where you've focused it. This is great to bring the focus to your subject and is often used for portraits, images of birds, and macros.

Also, keep in mind that your ISO plays a part in how your picture is exposed. Typically in low light, even with your aperture set at f1.8, you'll need to increase your ISO number. On my camera, the maximum ISO is 1600, so I'll set the camera to that, use aperture priority, and manually set the aperture to f1.8. That way, the camera will figure out the best shutter speed to use. You'll need a shutter speed of at least 1/80th of a second to shoot a sharp image with your 50mm lens (since there's a 1.5x modifier when dealing with DX style DSLR cameras.)

Dealing with aperture, shutter speeds, and ISO to get a good exposure is often confusing at first. Once you figure it out though, it really opens up your possibilities. To recap, for low light, make the f-stop or aperture use the smallest number possible, the highest ISO possible, and your shutter speed as slow as you can without compromising sharpness. For this lens on my Nikon D50, the settings then would be f1.8, 1/80th second or faster, ISO 1600. Modify it from there to your particular situation.

For another example of dealing with these three exposure components, see my review on a 500mm Sigma Telephoto lens.

I used this lens to capture images of wildlife such as deer, moose, and elk.  500mm was enough to get a close up shot of several large animals, while allowing me to keep my distance.  This made it possible to photograph the animals without disturbing them.  I used it in combination with a monopod for stability since the lens is bulky and heavy. 

Having the ability to go from 50 to 500 mm was a nice feature.  It gave me a lot of room to adjust to a situation, although to be honest, I was almost always using it at it's full 500mm focal length. 

To give you an idea of its magnification, the normal human eye sees at 50mm.  My digital camera has a natural 1.5x magnifier, which makes 500mm really 750mm.  In other words, objects become 15 times closer than normal.

The biggest the aperture can get at 500mm is f/6.3.  Typically, to shoot a sharp image, a person should shoot at a fraction of a section that is faster than the relative focal length.  In other words, at 500mm (really 750mm), to shoot a clear image, you should shoot at 1/800 second or faster.  I had a monopod, so I pushed it to 1/640 second on some shots, but even then I could tell the difference.  1/800 second at f/6.3 doesn't leave a lot of light for the camera, therefore, I was almost always shooting at my camera's highest ISO which is 1600.  This makes the shots a little grainer, but it's a price I had to pay to expose the image correctly.  Even still, some of the images required a little post production in Photoshop to get the exposure to the correct levels.

Here are two examples of photographs taken with the Sigma 50-500 on a Nikon D50:

Jumping Deer
Bull Elk

The lens costs around $1000 and I'd recommend it to anybody looking for a telephoto lens in that price range.