In focus?

If you have been photographying for a while you might have come back after a nice trip only to find that that brilliant landscape shot has been ruined because either the things in the foreground or the distant background is out of focus! And you wonder because everything looked alright on the LCD screen when you took it. Hehe. Well everything looks fine on the LCD, and generally you cant judge an image by looking at the LCD - except the histogram to see if you have overexposed or underexposed.

So what you need is to know how you get everything in focus - from the little flower in the foreground to the snow-topped mountain in the background. As most of you know, stopping down the lens to e.g. f/22 will do the trick, but you are still not guaranteed to have what you want in focus. Its because the focus point needs to be correctly placed to get optimum depth of field (DOF). Normally this means you need to manually focus. The focus point you are looking for is called the Hyperfocal Distance and will ensure you the longest distance in focus. Naturally this changes based on the focal length (mm) and the f-stop. Fortunately this is pure math and no magic involved, and some people have been so nice to make an online tool for calculating the hyperfocal distance. Try the link below and enter focal length and f/stop, then press the Calculate DOF button. The Hyperfocal distance will be shown. You can enter this in the Focus Distance and see that it will show you the closest Near Depth you get with Infinite Far Depth (thats where the snow-topped mountain is).

http://www.dudak.baka.com/dofcalc.html

For my 17-40mm, while shooting at 17mm, if I focus at hyperfocal which is 0.525 meters, I get everything from 0.263 meters to infinite in focus! Now that should bring everything in focus. Of course you also need a tripod for shots at f/22 or your images will be all blurry from camera shake. No point in fuzzying with hyperfocal distance then.

Note however that many lenses have a sweet spot where they perform best, that means that image quality is generally best at this f stop. On most lenses this is around f/8 and f/11. So if my foreground starts at around 1 meter you dont need to shoot at f/22 to get everything sharp. Actually, if I shoot with my 17mm at f/11 at the focus distance of 1 meter I get everything from half a meter in front all the way to the back in focus.

I've ruined one too many shot by relying on autofocus so now I am keeping a table for reference so that I can quickly find the hyperfocal distance at each f-stop at the most used mm ranges (usually this is 17mm).