A Closer Look at Magnification, or An Extended Look at Macro
Extension tubes are a great, straight-forward way to get into macro photography. Unlike our last post, which focuses on how to increase your depth of field with a macro lens, extension tubes reduce your minimum focus distance, allowing you to focus even closer than you would normally with a lens.
However, it should be noted that extension tubes come with their fair set of drawbacks. First, you will no longer have infinity focus (which you probably wouldn't need anyway, if you were purchasing extension tubes). More importantly, adding too much space between the lens and the sensor plane can place your focal point inside the lens, meaning that no matter how close your subject gets to the front of the lens, it'll never come in focus.
Manual Extension Tubes
Just like a brand new phone: no contacts
The most basic of extension tubes are metal tubes without any electronic features. These are usually quite affordable.
With a manual extension tube like this, the drawback is that you don't have any access to features that require an electronic connection, which can include the following:
- Automatic focus (though it should be noted that some lenses require electronic connection even for manual focus)
- Image Stabilization/Vibration Reduction
- Aperture control (in the case of Canon EF lenses and Nikon E-type lenses)
Our manual extension tubes consist of five components: a lens mount, camera mount, and three different-sized rings that can all be threaded together in any combination. It should be noted that because these parts are all threaded together, the lens is not usually in the correct orientation after everything has been mounted.
Automatic Extension Tubes
Usually costing more, automatic extension tubes do have electronic contacts, meaning all electronic features would be available. They also use a bayonet fit on both sides of each section, so installing them is no different than mounting your native lens (the lens is always oriented in the correct direction, too).
EXIF data is also transferred through the contacts, so focal length and aperture data can be viewed on files when reviewing images.
For our manual extension tubes, we tested a set of our Nikon extension tubes with our Nikon D810 and a Nikon 50mm f/1.8G.
For our electronic extension tubes, we were lucky enough to test a set of our GFX Extension Tubes on our GFX 50S with the GFX lens lineup (minus the 250mm), and we used this opportunity to compare and contrast how each lens performs for macro photography. All measurements below are approximate.
Minimum Focus Distance vs. Working Distance
Minimum focus distance is the distance between the subject and the sensor plane, while working distance is the distance between the subject and the front of the lens. For the most part, the two are correlated; the shorter your minimum focus distance, the shorter your working distance.
When using extension tubes, we absolutely recommend starting small and working your way up to larger extensions.
While focusing closer does help give a greater magnification to the overall image, you don't want to get too close, or you risk the camera or lens blocking light from hitting the subject.
Probably not the most flattering angle.
As mentioned above, extension tubes reduce your minimum focus distance, but how much of a change can one reasonably expect?
The easy answer is that there's no easy way to calculate offhand how much closer an extension tube will let you focus without a lot of math, thankfully extension tube calculators can be found with a little bit of Googling. Originally, we imagined that a 20mm extension tube would give the same change in minimum focus distance across the board, but that ended up not being true.
In the case of the 20mm extension tube, the change in minimum focus distance ranged anywhere from being able to focus 33mm all the way up to 580mm closer.
120mm f/4 (No extension)
120mm f/4 (w/ 20mm extension)
Focusing 33mm closer makes the ruler appear ~46% larger in the resulting image
100-200mm f/5.6 @200mm (No extension)
100-200mm f/5.6 @200mm (w/ 20mm extension))
Focusing the the 580mm closer makes the ruler appear ~93% larger in the resulting image
Despite the 120mm having the smallest change (MFD-wise), it actually gave the largest reproduction ratio. Of course these are simply numbers. When it comes down to it, lens design is the biggest factor in what your results may end up looking like. To see how the other lenses did, look below:
32-64mm f/4 @32mm
32-64mm f/4 @64mm
45mm-100mm f/4 @45mm
45mm-100mm f/4 @100mm
100-200 f/5.6 @100
100-200 f/5.6 @200
In the entire line-up, the 45mm f/2.8 ended up giving us the best reproduction ratio, once we stacked both the 20mm and the 48mm extension tubes. I would have guessed that the longer lenses would have had a better time with macro photography, but it ended up being one of the short lenses, after all.
This is all more for fun than anything. Different lenses fulfill different purposes, but who's to say you need a macro lens to do macro photography? Extension tubes do have their drawbacks and tradeoffs, but they do create some new opportunities without having to go out and buy a new lens.
- Fotodiox Staff