|Simple DoF Calculator|
Back in the days of manual 35mm SLR cameras, the lens manufacturers printed various colored lines on the barrel of the lens that matched up with similar lines on the focus ring. On each particular focal length lens, you could instantly see, based on the distance to the subject and the f/stop you selected, the distances where everything would be in focus. Say you were shooting a close-up of a flower you could see if the leaves in front or behind would be in or out of focus and, depending on what you wanted to achieve in the picture, either change the f/stop or to go to a shorter or longer focal length lens. Similarly, if you were shooting a landscape and wanted everything from almost at your feet out to infinity to be in focus, the lines on the lens barrel would tell you what f/stop adjustments you had to make to achieve the depth of field that you wanted.
Honestly, I shoot probably 25% of my pictures off of a tripod or a "bean bag" filled with foam peanuts. And, I Manual focus my D90 almost all of the times when it is on a support. I was going crazy trying to calculate depth of field to see what would be sharp (for me the Depth of Field preview button is worthless for finding precise DOF). I would shoot a picture and zoom it larger on the screen to try to see what was in focus; if I needed to change something I would have to recompose the picture with the new settings. That was until I discovered Depth of Field apps for my smartphone!
Depth of Field apps are available for Droid and iPhones - they sure make life easier. And they are usually free so you can try several and see which you like best. How they work is: you select your D90 from a list of cameras and select the focal length of the lens you are using. Then you select your f/stop and distance to the subject and the app tells you the closest and farthest distance that will be in sharp focus. And you can then make any changes to the camera/lens settings to achieve your desired results.
One more thing - like I said, these apps are almost all free. So, if you don't really understand Depth of Field, go ahead and get an app and just play with it. You don't have to pay for film or pay for the app, so shoot a bunch of pictures and switch lenses, f/stops, focus distances, shutter speeds and ISO and use the DOF app on your phone - before long it will all begin to make sense how all of these things work together and you'll begin to see your photographs moving to a whole new level.
Written By BayDogs