This +1 close-up lens will assist you to focus the lens closer compared to how it does presently; a +2 close-up lens allows you to focus closer compared to a +1 and it goes on with other higher factors.
The maximum magnification produced can vary depending on the focal length of the lens in addition to the actual close focusing efficiency of the lens it´s connected to.
Each individual glass surface is vacuum covered with a layer of anti-reflection coating. This particular layer assists to avoid internal ghosting and reflections. Additionally, it elevates light transmission from approximately 92% (from uncoated glass) to above 98%.
Source (http://www.photo24.co.uk)(images- Simon Johnson)