The macro extension tube is a tool in macro photography that hasn’t had much utilization. Most macro photographers opt for macro filters or reverse rings. But the macro extension tubes can work as well or even better than any other device that adds magnification to your lens.
I have been using the macro tube for over four years now. I got the cheap one by swapping it for a lens bag that I wasn’t using. I was a trade that changed my macro photography for the better. It takes a bit of time to get used to but once you master it, shooting will be a breeze.
What is it?
A macro extension tube is a steel tube that extends the distance between the rear element of the lens and the focal plane. The tube itself does not have any lens elements. It is literally just a tube and there are photographers who make their own extension tubes. Some extension tubes for macro do have electronic components to enable auto focus but are generally a lot more expensive.
Increasing the distance between the rear element and the focal plane shortens the minimum focusing distance of the lens. The closer your front element is to the subject, the more magnification you will get.
The main purpose of the macro extension tube is to increase the magnification ratio of your lens by shortening the focusing distance. The computation of the magnification is focal length / tube length. So a 50mm lens with a 50mm tube will get you 1:1 magnification ratio. If you double the tube length with the same lens, you will effectively double the magnification.
And yes, you can stack on as many macro tubes as you can. I have seen guys stack two or more tubes together to produce some impressive macro shots. There is a limit though for the magnification when using a wide angle lens which I believe is around 2.5x magnification. The best extension tubes in my opinion are made by Canon, Nikon and Kenko. All these brands have the electronic contacts and retain autofocus.
Once you attach a macro tube to your lens, you will find that when you look at the viewfinder it will be a bit darker than what you would normally expect. The downside of not having a lens element within your extension tube is that it does not transmit light that well. The longer the tube, the less light gets to the viewfinder prism and the sensor.
Another drawback is that the close your get to the subject, the less light there is available. Being so close, sometimes the subjects touch the front element already. The lens can also cast a shadow when you shoot with a flash.
How to shoot with an extension tube
Just like with any other macro photography technique, you set your lens to the minimum focusing distance and move the camera forward and back to get the subject in focus. Moving in and out rather than using the focusing ring will ensure that you are getting the maximum magnification for the subject.
With a macro extension tube, you will need to shoot at a shallower aperture. I normally shoot around f8 to f11 as it gets a bit darker when I go higher than that. You also need to shoot at a higher ISO to compensate for the extension tube light transmission. And it would be a good idea to have a flash with a diffuser attached.
My shooting style
Generally I set my camera to Manual (M) mode, with the shutter speed at around 1/100 or 1/200 depending on the conditions. The ISO will be around 800 to 1000 and the aperture at around f11. I set the flash to ¼ power then fire of a few test shots. I will then adjust the ISO, aperture and flash power to dial in the exposure.
Once I am satisfied with the exposure I will then go look for my subjects. I shoot from morning to mid afternoons when there is still enough light out. I don’t use a tripod or macro rail as it will limit my movement. That is the reason why I shoot at a high shutter speed. I use the Stoffen flash diffuser to soften the light from my flash and I don’t point the flash directly at the subject. Do avoid shooting in burst mode as the camera will tend to jerk.
Mastering the macro extension tube takes time. The first thing is to get the exposure right because lighting can be a bit tricky with macro photography. The second thing is nailing the focus. The last bit is to master the focusing distance.
So be patient, take your time and shoot plenty.