Recently I noticed that the autofocus of my Nikon 105mm macrolens did not perform properly and that the lens gave a high-pitched squeak. When I brought it in for repair I bought Caruba extension tubes so I could continue my macrophotography.
I had been reading a bit about extension tubes being a cheap way of doing macrophotography. The promise is that for 100 euros you can get a better a magnification than a 1000 euro macrolens. The basic idea is that the hollow tubes put the lens further away from the sensor, thereby reducing the minimal focus distance. So, you can take a picture from closer by. As a result of getting closer to the subject the magnification increases. Just as you would expect, if you put something right in front of your eyes it looks bigger than if you hold it at arm’s length. For example, 68mm of tubes gives 1.5 magnification for a 50mm lens. Notice, a macrolens only gives 1.0 magnification! It looks like paradise.
So, after unpacking I put my 50mm lens on all the tubes together (68mm) right away. I was shocked: the camera could not focus! After reading some more (in Dutch), I realised that the range in which the camera could focus was reduced from 45cm-infinity (without tubes) to a few millimeters at a distance of a few centimeters (with all tubes) in front of the lens. Understandable that the autofocus could not handle this. The subject was out of the focus range.
Getting sharp pictures in macrophotography is quite a challenge. The size of depth-of-field (DoF)—a portion of the range in which the camera can focus—depends of course on the aperture. So, we are talking about a millimeter or even less. In practice this means that when holding the camera in my hand, and by breathing and by keeping balance, the subject is getting in and out of focus continuously. So, you really have to try to press the button at the right time! Of course, you could use a tripod, however, that does not work very well with bees and butterflies flying everywhere. However, for flowers it works perfectly. I use my Peak Design Travel Tripod.
Furthermore, when using extension tubes you lose some light. Trying to get more DoF, to make focussing a bit easier, you choose a smaller aperture, which again means less light. The combination results in higher ISO. As a consequence, the dynamic range decreases and it introduces some noise in the picture, which becomes visible if you decide to crop to further increase magnification.
How about other lenses? It turns out that wide-angle lenses do very well as far as magnification is concerned, however, if you use too many tubes the focus area will end up inside the lens. Making wide-angle lenses almost useless for macrophotography. Telelenses, on the other hand, do not do so well as far as magnification is concerned.
My provisional conclusion is: Focussing in macrophotography is already a challenge, using extension tubes it is even more a challenge if you push it to the limits by using too many tubes.
My advice is to use mainly one of the smaller tubes (12 or 20mm). It already gives you a substantial magnification for mid-range lenses and you don’t have to put your lens right in front of the subject. Furthermore, you do not lose a lot of light.
In my next post I will share my experience with extension tubes and a zoom lens.