Mia, is this trick questions :)
They are very good.

In a optical microscope the shorter the wavelength the better we can observe microscopic structures.
It has to do with the reflective properties those structures express and the wavelengths they re-emit.
The long wavelengths will not reflect back as 'whole' wavelengths whereas the shorter more energetic will find 'place' inside those structures cavities and reflect back as 'whole' as I understand it.

" The resolving power of a microscope is ultimately limited by the wavelength of light (400-600nm for visible light).
To improve the resolving power a shorter wavelength of light is needed, and sometimes microscopes have blue filters for this purpose
(because blue has the shortest wavelength of visible light). "
This one is about the resolving power of different devices.

Then we have electronic microscopes whose wavelength are decided by the energized type of electrons used.
The more energized the shorter the wavelength and the higher the resolution of the final image.

" There are two types of electron microscopes: the transmission (TEM) and the scanning tunneling (STM) electron microscope.
In a TEM, a monochromatic beam of electrons is accelerated through a potential of 40 to 100 kilovolts (kV) and passed through a strong magnetic field that acts as a lens.
The resolution of a modern TEM is about 0.2 nm. This is the typical separation between two atoms in a solid.
This resolution is 1,000 times greater than a light microscope and about 500,000 times greater than that of a human eye."

This type was the first electron microscope used to see within the cells.
It sees only those electrons which pass through the subject and only those electrons which pass through the sample will be seen.
This gives you a picture of black and white with shades of gray.

" The STM is similar to the TEM except for the fact that it causes an electron beam to scan rapidly over the surface of the sample and yields an image of the topography of the surface.
The resolution of a STM is about 10 nm. The resolution is limited by the width of the exciting electron beam and by the interaction volume of electrons in a solid.

Resolution is the finest detail that can be distinguished in an image. The resolving power of a microscope is quite different from its magnification.
You can enlarge a photograph indefinitely using more powerful lenses, but the image will blur together and be unreadable.
Therefore, increasing the magnification will not improve resolution.
The minimum separation (d) that can be resolved by any kind of a microscope is given by the following formula:
d = λ/(2n sinθ) "

The problem with Electron microscopes is that your specimens will be dead as they have to be fixed in plastic and viewed in a vacuum.
Also they must be stained with an electron-dense chemical as they otherwise can be damaged by the electron beam.
Everything you ever needed to know about Transmission Electron microscopes

For your Crystals Electron diffraction seems to do the trick.
And there you will find X-ray diffraction too.

The next one is tricky :)
At least for me.

I believe you are referring to what commonly is called plano-concave lenses?
Will this help you?
http://en.wikipedia.org/wiki/Lens_(optics)

Look at
"If the lens is biconcave or plano-concave, a collimated beam of light passing through the lens is diverged (spread); the lens is thus called a negative or diverging lens.
The beam after passing through the lens appears to be emanating from a particular point on the axis in front of the lens;
The distance from this point to the lens is also known as the focal length, although it is negative with respect to the focal length of a converging lens."