Trouble w/ Focusing

[A Khun]

on christmas eve was the first event i used my 450d for. and i noticed that whenever i took a picture of more than 3 people, it would really only focus on the people in front of the camera, and i was wondering if there was a setting or anything for the camera that FOCUSES ON EVERYTHING! i really am a beginner at this type of stuff, so i really need some tips. my next event is new years, so i need to learn this quick, and thanks in advance!

[Franglais]

on christmas eve was the first event i used my 450d for. and i noticed that whenever i took a picture of more than 3 people, it would really only focus on the people in front of the camera, and i was wondering if there was a setting or anything for the camera that FOCUSES ON EVERYTHING! i really am a beginner at this type of stuff, so i really need some tips. my next event is new years, so i need to learn this quick, and thanks in advance!

There are two concepts here:

1. Depth of field. At a given aperture and focal length the image is only in focus between a certain range of distances. Say you're focussed at on something at six feet, there may only be sharp focus between 5 feet and 7 feet. There are two determining factors

1a. The longer the focal length (more telephoto) the smaller the depth of field. If you zoom in on just people's heads then you may find the person standing behind is out-of-focus. Stick to a normal (30mm) or wide-angle (20mm) focal length and a distance of 6 feet or more and most of a group will be in focus

1b. The smaller the aperture the greater the depth of field. I imagine you're using the camera's built-in flash at less that 10 feet. If you use 100 ISO then the camera will probably set the aperture automatically to f5.6 which gives you some depth of field. If you set the camera to 800 ISO you probably won't notice any difference in the picture quality but the camera might set the aperture to f11 which gives you much more depth of field

2. The focus zone. I don't know the 450D but it is probably set up to focus on the closest thing in the frame. You can take control and tell it to focus on something else for instance a person at mid-distance in a group

One final thought if you have come from a point and shoot - the focal length of the lens on a P&S is much shorter that on a DSLR (smaller sensor) so this is why you haven't had the problem up till now. But then you moved up to the DSLR to be able to get more control, have greater artistic effects like out-of-focus backgrounds - didn't you?

[Frog]

Franglais said it all.
The easiest thing for you to do is to use a smaller aperture to get more depth to the focus.
Another trick is to focus on something the same distance as your subject and then, move the camera to the composition you want. To use focus lock, you focus and then hold the shutter half way down while you compose.

[A Khun]

Thanks for the tips, i just tried doing some tests, and i can tell how much of a difference it makes. But i was wondering, people usually use 'aperture & depth of field' to help explain things. Ive been googling those terms, but what ive come across is never really the direct definition of what these mean. could someone explain more in detail what they mean, and give examples to help me understand better ?

[Dylan8i]

Check out this recent thread, its about bokeh, but has some very good explanations about DOF, and how to measure it and what controls it etc. bokeh, is the OOF background areas, where as you want the subject to be in focus, but they go hand in hand and use the same concepts.

Secret to Bokeh?


im a nikon guy, so it might not be the same, but my d200 has a focus mode where it focuses on the CLOSEST object in the frame... your camera may have a similar mode that you have turned on to....

[mn shutterbug]

Follow this link to a depth of field calculator. It's very informative.

http://www.dofmaster.com/dofjs.html