Question: Why do telescopes such as TRACE and SOHO use special mirrors to reflect Extreme ultraviolet?
About the article "Telescope", section "Types".

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The name "telescope" covers a wide range of instruments.
Most detect electromagnetic radiation, but there are major differences in how astronomers must go about collecting light (electromagnetic radiation) in different frequency bands.
Telescopes may be classified by the wavelengths of light they detect:
 X-ray telescopes, using shorter wavelengths than ultraviolet light
 Ultraviolet telescopes, using shorter wavelengths than visible light
 Optical telescopes, using visible light
 Infrared telescopes, using longer wavelengths than visible light
 Submillimetre telescopes, using longer wavelengths than infrared light
As wavelengths become longer, it becomes easier to use antenna technology to interact with electromagnetic radiation (although it is possible to make very tiny antenna).
The near-infrared can be handled much like visible light, however in the far-infrared and submillimetre range, telescopes can operate more like a radio telescope.
For example the James Clerk Maxwell Telescope observes from wavelengths from 3 μm (0.003 mm) to 2000 μm (2 mm), but uses a parabolic aluminum antenna.
On the other hand, the Spitzer Space Telescope, observing from about 3 μm (0.003 mm) to 180 μm (0.18 mm) uses a mirror (reflecting optics).
Also using reflecting optics, the Hubble Space Telescope with Wide Field Camera 3 can observe from about 0.2 μm (0.0002 mm) to 1.7 μm (0.0017 mm) (from ultra-violet to infrared light).
 Fresnel Imager, an optical lens technology
 X-ray optics, optics for certain X-ray wavelengths
Another threshold in telescope design, as photon energy increases (shorter wavelengths and higher frequency) is the use of fully reflecting optics rather than glancing-incident optics.
Telescopes such as TRACE and SOHO use special mirrors to reflect Extreme ultraviolet, producing higher resolution and brighter images then otherwise possible.
A larger aperture does not just mean more light is collected, it is collected at a higher diffraction limit.
Telescopes may also be classified by location: ground telescope, space telescope, or flying telescope.
They may also be classified by whether they are operated by professional astronomers or amateur astronomers.
A vehicle or permanent campus containing one or more telescopes or other instruments is called an observatory.
In the EUV portion of the spectrum (wavelengths shorter than about 30 nm) nearly all materials absorb strongly, making it difficult to focus or otherwise manipulate light in this wavelength range.
Telescopes such as TRACE or EIT that form images with EUV light use multilayer mirrors that are constructed of hundreds of alternating layers of a high-mass metal such as molybdenum or tungsten, and a low-mass spacer such as silicon, vacuum deposited onto a substrate such as glass.
Each layer pair is designed to have a thickness equal to half the wavelength of light to be reflected.
Constructive interference between scattered light from each layer causes the mirror to reflect EUV light of the desired wavelength as would a normal metal mirror in visible light.
Using multilayer optics it is possible to reflect up to 70% of incident EUV light (at a particular wavelength chosen when the mirror is constructed). 
Observations from some of the instruments can be formatted as images, most of which are also readily available on the internet for either public or research use (see the official website).
Others such as spectra and measurements of particles in the solar wind do not lend themselves so readily to this.
These images range in wavelength or frequency from optical (Hα) to extreme ultraviolet (UV).
Images taken partly or exclusively with non-visible wavelengths are shown on the "SOHO" page and elsewhere in false color.
Unlike many space-based and ground telescopes, there is no time formally allocated by the SOHO program for observing proposals on individual instruments: interested parties can contact the instrument teams directly via e-mail and the SOHO web site to request time via that instrument team's internal processes (some of which are quite informal, provided that the ongoing reference observations are not disturbed).
A formal process (the "JOP" program) does exist for using multiple SOHO instruments collaboratively on a single observation.
JOP proposals are reviewed at the quarterly Science Working Team ("SWT") meetings, and JOP time is allocated at monthly meetings of the Science Planning Working Group.
First resultshave been presented in Solar Physics, volumes 170 and 175 (1997), edited by B. Fleck andZ.
Švestka. 
Although optical telescopes can image the near ultraviolet, the ozone layer in the stratosphere absorbs ultraviolet radiation shorter than 300 nm so most ultra-violet astronomy is conducted with satellites.
Ultraviolet telescopes resemble optical telescopes, but conventional aluminium-coated mirrors cannot be used and alternative coatings such as magnesium fluoride or lithium fluoride are used instead.
The Orbiting Solar Observatory satellite carried out observations in the ultra-violet as early as 1962.
The International Ultraviolet Explorer (1978) systematically surveyed the sky for eighteen years, using a aperture telescope with two spectroscopes.
Extreme-ultraviolet astronomy (10–100 nm) is a discipline in its own right and involves many of the techniques of X-ray astronomy; the Extreme Ultraviolet Explorer (1992) was a satellite operating at these wavelengths. 
Arthur Bertram Cuthbert Walker, Jr. (August 24, 1936 – April 29, 2001) was a solar physicist and a pioneer of EUV/XUV optics.
He is most noted for having developed normal incidence multilayer XUV telescopes to photograph the solar corona.
Two of his sounding rocket payloads, the Stanford/MSFC Rocket Spectroheliograph Experiment and the Multi-Spectral Solar Telescope Array, recorded the first full-disk, high-resolution images of the Sun in XUV with conventional geometries of normal incidence optics; this technology is now used in solar telescopes such as SOHO/EIT and TRACE, and in the fabrication of microchips via ultraviolet photolithography.