We all love macro photography, this discipline that allows us to see what our own eyes cannot see. Unfortunately, it, which offers us such astonishing images, requires specific equipment that we often cannot afford. That’s why today we’re going to talk about close-up filters, which allow us to get started with macro photography without spending a fortune.
But today, we’re going to start at the end: before introducing you to these filters, we’re going to show you in 20 seconds everything they can do for you. Click on the video below:
You can see two images: one of them blurry, that of a lens without any filter installed. Here we are very close to the flower and the lens fails to focus. On the other image, the lens accommodates a close-up filter +4 and as you can observe, the flower does not only appear magnified but also very clear.
Close-up filters: what are they and what are they for?
These magical allies are known by various names: close-up lenses, close-up filters or macro filters. A close-up filter is basically a lens that screws onto the front part of your lens, in the same way as a circular filter, and which has very specific qualities that we will see later. You can find filters of different sizes, manufacturers and types on the market.
These filters are classified by diopters (+1, +2, +4…) which will give you different magnification factors and allow you to get closer or less to the element to be photographed.
Diopter: 1. F. Oh PT. Unit of power of optical systems which is equivalent to the reciprocal of the focal length of 1 meter.
Close-up filters perform two functions: enlarge the image with an incredible magnifying effect and reduce the minimum focusing distance of your lens. Thanks to this, you will be able to start taking your first macro shots without having to buy a specific lens for it.
Filters close-up on the test bench
To discover all the possibilities of these macro filters, we tested three of them: a close-up filter +1, a close-up filter +2 and a close-up filter +4. We installed these filters on an 18-200 mm zoom lens and we took as subject the flower the first blue flower. We will see for each of them, the before / after of their use.
These filters can also be used together by screwing on top of each other. The diopters are then added together and the effect is amplified to obtain better results. But beware, the sharpness will always be affected. Try to close the diaphragm as much as possible.
If it’s the exposure that becomes critical when you close the diaphragm (to gain depth of field), try to have good lighting conditions for the photo, whether natural or artificial. There are specific lighting accessories (continuous LED or flash) for macro photography: with a ring-shaped or lateral design, for the front part of the lens.
How to Calculate Minimum Focus Distance
You would probably like to know how much the minimum focusing distance will be reduced. With the following formula, you can calculate the minimum focus distance your lens will have after installing the close-up filter:
Formula to calculate the minimum focus distance: e = 1/ ((1/d) + D)
The formula may seem complex at first glance, but nothing could be further from the truth. e will be the new minimum focus distance (the one obtained after assembling the close-up filter); d is the current minimum focus distance of your lens. D is the diopter that corresponds to the chosen filter. You can make this formula at home before choosing a filter if you are looking for a very precise minimum focus distance.
Let’s take a practical example. Let’s imagine that we use the Tamron SP 90mm f/2.8 Di Macro lens, at the minimum focusing distance of 0.3 m, and that we want to reduce the latter even more. We place on this lens a close-up filter +4, for example. What would be the minimum focusing distance? We apply the formula:
e = 1/ ((1/d) + D) = 1/ ((1/0.3) + 4) = 1/ (3.3 + 4) = 1/ (7.3) = 0.1369…
As you can see, with the +4 close-up filter installed, we managed to reduce the minimum focusing distance from 30 cm to 13 cm.
Advantages and disadvantages of close-up filters
Of course, close-up filters have their limits: sharpness becomes critical as you enlarge the image (but this is a general problem in macro photography, not just specific to close-up filters). We can overcome the problem, as we have seen, by opting for closed diaphragms (provided that the photos are taken at times when the natural light is intense or that an additional light source is used, otherwise to have underexposure problems).
On the side of the advantages, these closer lenses allow you to take your first steps in the world of macro but without spending a fortune. They are economical and very easy to use accessories and they save us from having to change lenses. Finally, they are small and light (easy to carry), so snapping flowers in the park is easy.