I want to take image of a dried droplet 12 mm x12 mm

The fundamental problem with taking very close photos, or macros, is that run-of-the-mill lenses won't focus that close. Their closest image plane would be farther away than the sensor in the camera.

Note that macro photography is officially defined as at least one-to-one, but that's not important.

So what do you do?

• Get an expensive Macro lens
• Get a set of close up adapters, magnifying glasses, that screw on like filters
• Get some extension tubes

The last option of extension tubes can be very inexpensive. They are exactly that, tubes that extend the lens out farther so it can focus on the sensor. They have no optics, just open tubes with mechanical couplers for your camera. They often come in sets that can be stacked. For example:

Nikon Extension Tube Set $10

Canon Extension Tube Set $10

You will of course need a tripod, and lighting can be very tricky for macro photography.

Good Luck!

It looks like your crystals are not nearly as lacy as the ones in the left pictures. I don't know what to do about that.

Cannon makes several macro lenses designed just for this. The usual definition of a macro lens is that the image on the sensor is the same size as the object, so you would be covering half the width and a third the length of a full frame sensor or most of the width of an APS-C sensor. Some lensed designated as macro do not get the image this large.

The focus is critical, so it will help a lot if your crystals are very thin. It can be hard to get even illumination because the camera gets in the way. Mount the camera on a tripod and take long exposures as nothing is moving. Use manual focus with the multiplied view on the screen to get it right. You could also take a series of photos, moving the focus each time.

Try putting your object on a flatbed scanner, you will be surprised. At 600 dpi you'll get 300 x 300 pixels, which is not terribly bad. The illumination is quite favorable, mainly because it scans too.