Example of short depth of field
This picture might look a bit crazy, but I just wanted to point out how using a shallow depth of field can make a much more dramatic image. The reason I decided to blog this, I had a client the other day asking me why in my pictures the background is really blurry and some other photographers had everything in focus including the background, and he of course liked my look. So I thought I would briefly explain what is happening. The effect you are seeing in this image is called a shallow depth of field. As you see only a very small area of the image, ideally the eyes are in focus, and as you move into the foreground or background the focus quickly blurs. A short depth of field is typically considered to be very desirable in a portrait because it highlights the subject and can make for a beautiful out of focus background or bokeh.
This image was taken with a Nikon f2.8 ED lens that zooms from 24-70mm. This lens cost about $2000 and it’s very large and heavy, so it’s not something that the average person that doesn’t do this for work is going to want to buy and carry around. I can’t explain to you all the physics of how a lens works, but all you really need to know if the lower the f-stop number, in the case of professional portrait zoom lenses it’s almost always f2.8, the wider the aperture and the shorter the depth of field. The aperture is similar to our pupil, it expands and contracts to control the amount of light entering a lens. If you want to learn everything about the aperture you can visit wikipedia. Typically the larger a lens is the bigger this aperture opening can be and the more light the lens can focus on the sensor that records the image.
Diagram from Wikipedia of lens aperture
To get the effect you see in the image above, you need either a really expensive zoom lens like I was using, or a prime lens. A prime lens is fixed, it doesn’t zoom. For example a $100 50mm prime lens has an aperture of f1.8. That means it can let in much more light and has even a shallower depth of field than my expensive zoom. There are other features of a good lens that make the out of focus area or bokeh look nice, but you can get a fantastic looking image out of even a cheap prime lens as long as you don’t mind zooming with your feet. I tend to prefer zoom lenses most of the time because weddings and family pictures can be so hectic and I’ve got to get the shot very quickly, but if you have the time and flexibility a prime lens will give some of the best images possible.
To sum it up, if you want beautiful images for cheap, get a DSLR and a 50mm f1.4 or f1.8 prime lens depending on how much you want to spend. You will have a camera that can take images that rival just about anything. If you’re a pro you really need to invest in the Nikon 70-200mm and 24-70mm ED prime lenses like I have in addition to primes. This gives you the flexibility to zoom and get a short depth of field and low light sensitivity. I think as my client mentioned, some photographers just don’t have the budget for good lenses, or if they have them they don’t know how to use them. I hope this helps explain a bit how good lenses benefit an image.
