For newbies in the photographic world: Petapixel.com published a very good article: Depth of Field Explained. In fact it is so good that it leaves nothing for me to add. 🙂 Just read the article and you will know everything you need to know about Depth of Field.
It is up to your own creativity and photo equipment to experiment with it. Just shoot and review. When the results are up to your taste, you have figured it out.
The article is not only about DOF. It gives you in insight how to work with Aperture and explains those F numbers on your (kit)lens.
In general it works like this: Set your camera to A (Av on Canon) mode. With one of the selection dials you can now scroll to the F number of your desire. On your lens you can read what the minimum and maximum F numbers are. On many kit lenses, like the Canon 18-55mm, the F numbers ar F3,5 – F5,6. Meaning at 18mm you can go as low as F3,5 and zoomed out to 55mm you have F5,6 as minimum aperture. The lower the F number, the more shallow DOF. So at F1,2 (Canon 50mm F1,2 L) you can have a serious small DOF, creating that blurred background that we call ‘Bokeh’.
The picture below is shot with an Canon 70D and a 18-135mm lens. The lens has an aperture of F3,5 at 18mm and F5,6 at 135mm. To get better object isolation you can use a ‘longer’ lens. Meaning: 50mm and up. The wider your lens, the more you get in the photo (frame), the longer the lens you get less in the photo (frame). The shot below was shot at 135mm at F5,6. If I used a different lens, for example my 70-200mm F2,8, I could have managed to get more and/better Bokeh. (background blur). If I have moved back a bit but keeping the same focal length on the camera lens (135mm) I get a bit more in the frame and more of the white flowers were in focus.
These are all things that you can experiment with. Up to your likes. So go out a try, shoot some photos. Shooting is practice, reading is learning.
There are lenses in various price ranges. In general Prime lenses, especially the ‘fast’ ones with an aperture of F1.2 up to F1.8, can give you a very nice blurred background. Many of these lenses are used in Portrait Photography. Zoom lenses are general not that fast, the fastest are the 24-70mm F2.8 and 70-200mm F2.8. (and they cost quite some money). You have some lenses that are faster like the Sigma 18-35mm F1.8 but is build for a cropped sized sensor.
If you want to learn how to use background blur and play with DOF, get yourself a standard 50mm F1.8 or F1.4. They are not breaking your bank account and offer good image quality.
The original article was written by Alexander J.E. Bradley and is the founder of Aperture Tours