Yes. They are too small to be seen with even the best optical microscopes.
None can. They have to be seen using a electron microscope.
Since a virus is far smaller than a typical cell (much smaller than a prokaryote) a virus cannot be seen by a regular microscope. To see a virus, you should get an electron microscope.
Viruses can only be seen with electron microscopes
SARS is a virus, requiring an electron microscope to be seen.
only under an electron microscope wiki it
As viruses cannot be seen with the optical microscope, electron microscopes are used. All the "lenses" in an electron microscope are magnetic fields produced by electromagnets and/or electrostatic fields produced by electrically charged metal plates and/or rings.
AIDS is the disease caused by the virus called HIV. It can not be seen under a light microscope (as one in the class lab) but you must use an electron microscope as they are very tiny.
An electron microscope is typically used to see a flu virus. This type of microscope uses a beam of electrons to create a high-resolution image, allowing for the visualization of very small structures like viruses.
A Virus called Prion was considered the smallest microorganism until recently. Though the microorganism hasn't been named yet biologists are pretty positive that it is the smallest microorganism. Follow the related link and take a look at the article.
Only the largest of viruses (e.g. Pox viruses) can be seen with a good light microscope (albeit with poor detail). Viruses usually can only be seen by electron microscopy. [2nd year Dental student, Naser]
Because of their very small size Viruses can only be seen via an electron microscope.
Some viruses can be seen without an electron microscope using a light microscope. These include larger viruses such as herpesviruses and poxviruses, which may be visible at higher magnifications. However, smaller viruses like influenza or HIV typically require an electron microscope for visualization due to their size.