Sometimes you just can’t get close enough to your subject. As a photographer, you can overcome this by zooming in with your lens and/or just physically getting closer. But you can only get as close as your lens will focus (i.e. its minimum focusing distance).
Those are the problems, so what about some solutions? If you are using a very sharp lens, you can sometimes add a teleconverter to magnify the image (i.e. a 2x tele-extender doubles a 500mm lens to 1000mm).
But what if you still need to get closer buy your camera won’t focus any closer? You can add an extension tube.
In this Costa Rican jungle I could not get physically close to this little “blue jeans” poison dart frog to photograph him with a macro lens, so I gave it a go with my 500mm lens (which is very sharp) + the 2x teleconverter, to give me an effective focal length of 1000mm. Adding a 35mm extension tube let me focus 2-3 feet closer. Using a tripod, cable release and close-focusing with “Live View” to really fine-tune the focus, I managed to get this image perfectly sharp on the frog’s eye.
Strawberry poison-dart frog (Oophaga pumilio), “blue jeans” color morph, La Selva Biological Reserve, Costa Rica. Canon 1DX. 500mm lens + 2x teleconverter and extension tube. ISO 1600. f/8 at 1/25 second. Ev +2/3.