how to get the whole image in focus

Started Aug 28, 2010 | Discussions thread
PDine Contributing Member • Posts: 579
Re: how to get the whole image in focus

Helen wrote:

Ema2010 wrote:

Well, perhaps , I will end up getting a serious lens with smaller aperture , I doubt my furhter playing around with a kit lens can do better.

Thanks for your input,

You probably can do better (and learn more) by setting the camera to Av and comparing your results by varying the aperture to learn the effect it has, as someone suggested above. The camera will compensate in this mode by altering the shutter speed automatically to keep the exposure right (within practical limits), so it's not too difficult.

Just to clarify: smaller apertures (to give you a deeper area in focus) have LARGER numbers (e.g. f16 is considerably smaller than f4) and all lenses have small apertures available in their aperture range - more serious/expensive lenses tend to increase the scale at the large aperture end (which gives you less depth of field - the amount in focus in front of and behind the object actually focussed on). So there's no need to look for a more expensive lens to get more in focus.

Some general rules of photography are a combination of the following:

You get more depth of field with smaller apertures;

You get more depth of field with wider angle lenses (i.e. the 18mm end of your standard kit zoom gets more in focus in front of and behind the subject at f8, for example, than the 55mm end does at f8, when the subject is at the same distance in both cases);

You get more depth of field with increasing shooting distance - so if you shoot something close up at the 55mm end at f8, LESS will be in focus in front of and behind it than if the lens is used at the same settings (55mm and f8) but focussed on something 20 feet away.

Though a longer lens, or zoom lens setting (say 55mm in this example) magnifies your subject more, bringing it apparently closer in the shot taken, it will generally not be able to focus as physically close as a wide angle lens (or the 18mm end of your standard zoom). But you have to experiment to see how large you can make your subject in the frame by juggling physical distance against zoom settings.

As you have already found out, compact cameras allow you to keep much more in focus (and to shoot closer as well), due to having smaller sensors which means their lenses have shorter focal lengths for the same subject magnification (making them act far more "wide angle" when it comes to focusing characteristics, to over-simplify).

I think you've given the best explanation there Helen. As you say - no extra lenses should be required. Your advice about using Av mode and shooting the same image at 18mm, starting at F3.5 and working down towards F20 would definitely be the best place to start IMHO.

As others have said though, as your aperture gets smaller, your shutter stays open longer. If the shutter speed drops below say 1/30 of a second at 18mm, you run the risk of adding motion blur. If your kit lens is the "Image Stabiliser" version, you might be able to go much slower than that without too many problems.

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