The other day I was asked to take some pictures of snails which got me thinking about the perils of close-up photography in general.
The first problem we need to look at is, how close the lens will focus. Lenses have a minimum focus distance which varies considerably from lens to lens, some longer zoom lenses have a 'macro' setting and will focus quite close but most lenses will not focus close enough to take the picture on the right.
If the lens you are using will not focus close enough there are a couple of ways to make it do so. If the lens is detachable from the camera, you can use 'extension tubes'. These usually come in a set of three which can be used separately or together. They fit between the lens and the camera body and, as the name suggests, there is no glass in them, they merely serve to move the lens further away from the film plane (or CCD on a digital camera). The lens will now focus on closer objects than it would before but will no longer focus on infinity.
Extension tubes are a good solution as you are still using the quality lens that you paid so much money for and so the picture quality will be the same as for any other shot. The downside (there's always a downside, you never get anything for nothing) is that you need more light (the inverse square law works just as well behind the lens as it does in front), either a longer shutter time or a wider aperture. Your meter will automatically compensate for this but it can lead to severe depth of field problems which we will discuss in a couple of paragraphs.
Close-up lenses are a bit like reading glasses, they are attached to the front of the lens and their strength is measured in diopters. So a +2 diopter lens will focus closer than a +1 etc. Using close-up lenses solves the problem of needing extra light but now you have something on the front of your lens. The front element of your lens and the beautiful multi coating on it, that you paid a fortune for and have lovingly looked after, are not being used. The quality of your photo is now, to some extent at least, in the hands of your close-up lens. So make sure you buy a decent make, they are not expensive so there is no need to buy the cheapest.
Depth of Field
Whichever method you choose to get your close-up, the mere act of focusing on close objects narrows the depth of field down to problematic levels. Any kind of wide aperture setting becomes out of the question if you hope to get the whole object in focus. If your subject is static and you have a tripod you have the option of shooting at a slow shutter speed and therefore a small aperture, but if not, you need a lot of light. Either sunlight or flashlight will do (I used a small studio flash for the snails), but you must get the aperture ring closed down to f22 or whatever your smallest aperture setting is. Even then you will find that sometimes this is not enough and part of your subject is still out of focus. Well, if that's the case, then it's time to make a decision about which parts of the subject most need to be in focus.
All other things being equal, I would almost always choose to have the parts nearest to the camera in focus and let the background and parts furthest from the camera go out of focus. This to me looks less like a mistake than a picture where the foreground is out of focus. There are always exceptions and one I can think of is an extreme close-up of a face, if I had to choose between the eye(s) being in focus or the nose, I would always choose the eyes because they are a more important part of the face.
There are times of course when a shallow depth of field can be very effective. I'm quite fond of this flower shot because the stamens really stand out against the out of focus petal. I also like the area of sharp focus on the right. It is usually considered to be a bad thing to have two focal points in a picture but in this instance I think it works quite well. To me, the main center of interest is the right hand side with the lovely crisp water droplets.
This was a very dull day just after the rain, I had no tripod and so could only manage 1/60th at f8. I must admit that if I could, I would have tried to render the whole flower in focus but I like this the way it is.
It is also a good illustration of photography in muted lighting conditions. I am usually an advocate of strong sunlight but here it would have caused problems with too much contrast, making these beautiful colors difficult to render.
If you want to read more on the subject, there's a very thorough article on macro photography on our blog written by Kev Vincent.
You could also try this book about close up photography