A shallow depth of field creates the blurry background effect. What some people might call the vignette effect. Continuing, where I say "DOF", I am referring to SHALLOW DOF, which is the more correct term for the vignette effect.
To begin, let's just get this out of the way. I'm a Nikon fan. I know Canon fans and Nikon fans are extremely devoted, some even rabid. I won't go into which camera is better. But, I do like Nikons much better. I am going to talk about some pictures that I shot with a Canon midrange G12 and a Nikon DSLR 5200. When I bought the Canon, it was the quality that I could afford at the time. It never was really up to par. But, I am comparing apples and oranges here, so let's forget about the brands. The point is my Canon is a step up from a point and shoot and my DSLR is an entry level DSLR.
My friend's pictures are really great because her jewelry is always the center of attention- or, some point of it. Whatever she wants you to see is in sharp focus and the rest isn't. If you are really, really good, you can do this with photoshop, but it will never look quite as good as if you had done it in camera and it will take a long time.
In the simplest terms, shallow DOF is achieved with low f numbers. If I get more complicated, it just gets confusing- so, just remember- You want the lower f numbers for good shallow DOF. The lower the number, the more blur in the area outside the point of focus. But, the lower the number- the more light you will need, too. Keep reading for more on that.
(For those of you who really understand cameras- just go with me here, I'm trying to keep it simple.)
Shameless plug- All of these pieces are available in my shop.
Here are some pictures I threw together using a light tent and color correct bulbs. I manually set the white balance on each camera. (That is another subject.)
This picture of an agate piece was taken by the Canon. You can click to enlarge. It is cropped from the RAW image.
Below is the adjusted image. All I had to do was bump up the light and contrast 5 points- not much, at all. The DSLR is very good at gathering light.
You see how the rocks are now fuzzy and seem to actually slip into the background, creating a 3-d look. The agate is the most in focus. Which is what I want.
I chose to show you a few of the most difficult rocks for me to photograph. With the Canon midrange, it took forever to get the best shots, which still required lots of post processing. I don't like to do much post processing because I run the risk of the picture not looking like the piece. I always used Aperture Priority on the canon because that is the setting that allowed me to adjust the f number. I used the smallest number available, but it wasn't small enough for really great effect.
With the DSLR, it is super easy to dial in a lower f number and use manual to gather the light I need in a light tent. On manual, there is a nifty little sliding scale that tells you if your image is under or over exposed. All you have to do is adjust the f number and/or the exposure time to get the right exposure. A longer exposure time allows more light to enter the lens. It couldn't be any easier and I get consistently good results.
Here's another set of Canon pictures. This bloodstone was extremely hard to get a good picture of. Getting the exposure right turned out to be impossible with this mid range camera in a light tent.
First is the cropped RAW image, second is post processing. I like to have white backgrounds because they look best online- at least, I think so anyway.
Here are the DSLR images cropped and processed.
Notice again the DOF and how it makes the stone pop. Notice, too that the "blood" shows up much better and is much closer to the real thing.
Here are two Montana agates that were really hard to photograph.
Canon: (I even had to use a handheld light to shine on it!)
Both are in front of white backgrounds for a backdrop to the pattern in the stone. The DSLR gathers more light and does a better job of revealing the stone's true character. The DOF also helps the stone pop.
And for the last one, another Montana agate. (Never mind the dust.) :
.... and DSLR
I think this comparison was the most dramatic. I always found Montana agates hard to get, but with the DSLR, it is really easy.
So, if you are still reading and you have a camera that will allow you to select "AV" or Aperture Priority shooting mode, dial in a low f number and start shooting. You will need to bring the camera back a little to allow it to gather more light. If you have enough pixels, you can easily crop in your image.
If you can afford it and you are ready to step it up a notch, get a DSLR and don't be afraid to go full manual. It, honestly, is very easy to use. It'll take a little while to learn the buttons, but it will so be worth it.
If you are in the market for a camera, go to Ken Rockwell's site. He has, what I have found to be, the best review site online. Do yourself a favor and look for a tilt monitor. I, initially, bought the D3200 and promptly returned it for the D5200 which has the articulated monitor. You can usually find really good deals on cameras which are a few years old and are still perfectly good cameras. Remember that you need higher mega pixels to crop in without loosing definition. And, for a mid range camera, you'll want macro capabilities, though most all have it. (It is usually the setting with a flower.) With a DSLR, it is the lens which will need to be macro. However, true macro, when talking about lenses, is different from the macro function on a camera. You will likely NOT need a true, expensive macro lens. I don't have one and I have no troubles. The 18-55mm Nikkor lens bundled with my camera worked fine, but is bulky, so I got the all purpose 35mm Nikkor lens. Ken Rockwell recommends it, so I got it and it is working fine.
Hope this was helpful. I found most of my research on DOF to be daunting, so I really wanted to write something simple and easy to understand. :)