How filters work
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Also known as close-up lenses, close-up filters prove to be convenient filters to have at hand. By installing these filters on whatever lens you are using at the moment, you can easily but effectively shoot macro. Or, by installing them on your macro lens, you can further shorten the working distance and get closer to your shooting object, thus making it look bigger on the final image.
A close-up filters set generally comes with four filters in four diopter values: +1, +2, +3 and +4. The higher the diopter value, the more you can shorten the shortest focusing distance. You can also combine and use 2 or more close-up filters together.
As a point to take in mind when using these filters, close-up filters come with their own close-up power, and the range in which you can close up on your shooting object and still have it in focus is quite limited. Therefore, even if combining with a lens in a lower shortest focusing distance value, you cannot expect a much better result.
On the other side, when combining with lenses devoid of macro shooting function, like high magnification zoom lenses, double zoom kit lenses or tele lenses, the advantage is enormous as macro photography will be effectively possible.
When you cannot carry all your lenses with you, close-up filters are definitively a photographic accessory worthy tucking in your bag.