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\begin{document}
\begin{center}
{\Large\bf
       The Extreme-Ultraviolet Imaging Telescope \\
       for the SoHO Mission \\
\vspace*{0.2in}}			% End of boldface
                                  EIT Team \\
10-June-1995 Version
\end{center}
\section*{Abstract}

     The Extreme-ultraviolet Imaging Telescope (EIT) will provide wide-field
images of the corona and transition region on the solar disc and up to 1.5 
solar radii above the limb. Its normal incidence multilayer-coated optics 
will select spectral emission lines from FeIX (171 \AA), FeXII (195 \AA), FeXV
(284 \AA), and HeII (304 \AA) to provide sensitive temperature diagnostics in the
range from $6 \times 10^4$ K to $3 \times 10^6$ K\@. The EIT will probe the coronal plasma
on a global scale, as well as the underlying cooler and turbulent atmosphere,
providing the basis for comparative analyses with observations from both 
the ground and other SoHO instruments. This paper presents details of the 
EIT instrumentation, its performance and operating modes.



\section{Introduction}

     The EIT (Delaboudiniere et al., 1989) is designed to image solar
structures in four narrow bandpasses that are selected to provide temperature
sensitivity to plasmas in the range from 0.06 to 3 MK\@. In this way, the EIT is
able to obtain images of the magnetically confined hot plasma in coronal loops
as well as much cooler material in features such as the chromospheric network.
Thus, EIT will provide sensitivity to solar structures an order of magnitude
lower in temperature than the spectacular imagery obtained by the Soft X-ray
Telescope (Tsuneta et al., 1991 and papers in PASJ, 1992) on the Yohkoh mission,
while maintaining overlap with that instrument's capabilities in the 0.6 to 3
MK range. The EIT will obtain full disk solar images in passbands nominally
centered  at 171 \AA, 195 \AA, 284 \AA\ and 304 \AA\ over a 45 arc min square field of view
with a spatial resolution limited only by the 2.6 arc sec pixel size of the CCD
image sensor. These data will provide a basis for the study and interpretation
of spatial and temporal fine structure in the solar atmosphere. Full disk
images obtained by the EIT will provide the global context required for aiding
interpretation of the coronal observations of other SoHO investigations and
same-day images will provide the basis for forming their near-term observing
plans. Also, the EIT capability of obtaining full resolutions partial frame
images of small regions of the disk in rapid cadence will define the structures
observed by SoHO instruments with narrow fields of view that are performing
spectral measurements. 

\section{Scientific Objectives}

     The primary scientific objective of the EIT is to study the dynamics 
and evolution of coronal structures over a wide range of time scales and 
temperatures to bring new insights into the study of mechanisms responsible 
for coronal heating and solar wind acceleration.
     While instruments on the Yohkoh mission have been designed primarily for
study of energetic solar phenomena such as flares, the EIT and several other
SoHO spectrographic instruments are designed for study of lower temperature
features of the sun that are appropriate for observations near solar minimum.
Thus, EIT observations will complement those of Yohkoh's Soft X-ray Telescope
by extending them to structures in a new lower temperature regime where the
images may better correlate with those obtained in the photosphere. Thus, EIT
observations may provide a much better link between coronal and photospheric
features. Also, EIT observations from the SoHO position at the L1 Lagrangian
point will allow data continuity uninterrupted by the earth occultations that
occur in observations from low earth orbits. This will allow access to a
frequency domain in dynamical analyses that has been previously inaccessible in
soft x-ray and EUV observations due to such periodic gaps in the data. 

                          (Ken Dere edit and expand)

\section{Instrumentation}
\subsection{Instrument Overview}

     The EIT is a telescope of Ritchey-Chretien design and will obtain full
disk images in four narrow passbands with a field of view 45 arc min square.
The EIT uses four separate multilayers that are deposited on matched quadrants
of both the primary and secondary mirrors of the telescope to define the
bandpasses by normal incidence interferometric reflections. These passbands are
nominally centered at 171 \AA, 195 \AA, 284 \AA\ and 304 \AA\ to primarily image the emission lines of
Fe IX, Fe XII, Fe XV and He II, respectively. A rotating mask allows only a
single multilayer coated quadrant of the telescope to be illuminated by the Sun
at any time. All of the multilayers are fabricated from alternating layers of
molybdenum and silicon. A sketch of EIT illustrating these features is shown in
Figure 1. A photograph of the flight instrument appears in Figure 2a and a
schematic of EIT is shown in Figure 2b, indicating its major subsystems. The
image from a selectable single EIT quadrant is focused on a back-illuminated
CCD whose detection efficiency at extreme ultraviolet (EUV) wavelengths has
been enhanced by a special fabrication process. Since each quadrant of the
optics forms an image on a single CCD the registration of the images is
accomplished automatically. A heat reflecting filter composed of 700~A of
cellulose sandwiched between 1500~A thick films of Al covers the EIT entrance
aperture. The telescope has a filter wheel near the focal plane that has two
filters to block long wavelength solar rays, an open position and two opaque Al
sheets that block the upper and lower halves of the reflected solar image,
respectively, from reaching the CCD\@. These opaque sheets allow the CCD to be
operated in a frame transfer mode to provide a redundancy to shutter operation,
but imaging only half the sun at each exposure. The exposed half of the CCD is
transferred to the occulted half in a time of 50 ms. The computer and
electronics that control the EIT instrument are contained in the LASCO
electronic box (LEB), with a common interface to the spacecraft command and
telemetry system. Consequently, the EIT and LASCO instruments share combined
EIT/LASCO telemetry rate of 1 + 4.2 Kbps= 5.2 Kbps. Operationally, the 3 LASCO
telescopes and the EIT can be treated as a single instrument package of 4
telescopes. This provides considerable flexibility in operating the EIT/LASCO
combination, but also introduces a few constraints. An addition telemetry rate
of 20 Kbps can be made available for short time periods from the CDS and SUMER
instruments for purposes of obtaining timely images for planning their
observing programs. Further details of EIT are given in Table I\@. 

\begin{figure}[p]
\vfill
\begin{center}
                        {\bf Table I: EIT Characteristics}

\medskip
\footnotesize\setlength{\baselineskip}{11pt}
\begin{tabular}{ll}
\multicolumn{2}{c}{Telescope (Ritchey-Chretien)} \\ \hline \noalign{\vskip 2pt}
    Mirrors                   &             Multilayer coated zerodur            \\
    Multilayers               &             Mo-Si tuned to different wavelengths \\
                              &             \quad on each of 4 quadrants             \\
    Bandpass centers          &             171 \AA, 195 \AA, 284 \AA\ and 304 \AA\\
    Bandpass selection        &             Rotatable open quadrant shutter      \\
    Effective focal length    &             $165.2 \pm 0.2$ cm                   \\
    Primary diameter          &             12 cm                                \\
    Geometrical area per quadrant &         13 cm$^2$                            \\
                              &          \\
\multicolumn{2}{c}{CCD detector (cooled to $-80$ C)} \\ \hline  \noalign{\vskip 2pt}
    Architecture              &            Three phase, multi-phase-pinned,      \\
                              &             \quad  back-illuminated,  enhanced   \\
                              &             \quad EUV sensitivity                \\
    Array size                &            $1024\times1024$ ($45\times45$ arc min)\\
    Pixel size                &             21 \micron\ square (2.6 arc sec)     \\
    Full well                 &             $>150,000$ electrons                 \\
    Readout rate              &             $5 \times 10^4$ pixels/sec           \\
    On chip summation         &             $2\times2$ and $4\times4$ pixels     \\
    Full frame readout time   &             21 sec                               \\
                              &          \\
\multicolumn{2}{c}{Filters} \\ \hline  \noalign{\vskip 2pt}
    Entrance Filter           &             1460 \AA\ Al/700 \AA\ polyimide      \\
    Filter wheel              &                                                  \\
    \quad Pos.~0              &             1500 \AA\ Al                         \\
    \quad Pos.~1              &             1500 \AA\ Al/700 \AA/cellulose/1500 \AA\ Al \\
    \quad Pos.~2              &             CCD bottom half blocked              \\
    \quad Pos.~3              &             Open, no filter                      \\
    \quad Pos.~4              &             CCD top half blocked                 \\
    CCD stray light filter    &             1500 \AA\ Al adjacent to CCD         \\
                              &          \\
\multicolumn{2}{c}{Telemetry} \\ \hline  \noalign{\vskip 2pt}
    Normal average rate       &              1 Kbps                              \\
    EIT/LASCO combined rate   &              5.2 Kbps                            \\
    Enhanced (from CDS and SUMER)&          26.2 Kbps (30 mins per 24 hrs)       \\
    Data Compression (square root) &        14 bits to 7 bits                    \\
\noalign{\medskip}
    \multicolumn{2}{c}{Image Transmission Time (assuming compression 7 bits/pixel):}\\
       Full Frame Unsummed (1 Kbps) &                                            \\
       \quad Normal TM                 &        2.0 hours                           \\
       \quad Enhanced TM (short periods)&       4.6 minutes                         \\
       Full Frame Summed $4\times4$ pixels &                                     \\
       \quad Normal TM                 &        7.6 minutes                         \\
       \quad Enhanced TM               &        17.5 seconds                        \\
\hline
\end{tabular}
\end{center}
\vfill
\end{figure}

\subsection{Optics}
\begin{verbatim}
       Fig. 3 Image of Wire Grid Illuminated by 304 A Light
       Fig. 4 Best estimate of point spread function in visible light

                   (J. P. Delaboudiniere/J. Brunaud)
\end{verbatim}
                   
\subsection{CCD Image Sensor}

The CCD used to record the EIT images is a thinned back-illuminated device
fabricated by Silicon Imaging Technologies Inc.\ (formerly a group within
Tektronix). The back surface has been processed to provide a high and stable
EUV quantum efficiency. The CCD is a $1024 \times 1024$ array of 21 \micron\ square
pixels with gate implants to provide Multi-Pinned Phase (MPP) operation. This
provides lower thermally generated dark current and improves the radiation
hardness of the CCD\@. There are four readout ports, at the corners of the image
array, with only one used at any time. The full well capacity of a pixel is
about 150,000 electrons and the charge transfer efficiency of the device is
about 0.999995 for low signal levels. The CCD is mounted in a special ceramic
package with provision to position its surface accurately and reproducibly in
the EIT focal plane. The CCD is cooled by passively radiating to deep space and
temperature regulated at $-80$~C by a small heater. This heater may also be used
to warm the CCD above ambient temperature to evaporate any condensates that
may have formed on its surface and that could degrade its EUV quantum 
efficiency. A temperature sensor is located on the ceramic package and another
is present on the CCD itself.


\subsection{Camera and Control Electronics}

As indicated earlier, the EIT is operated in concert with the LASCO instrument
on SoHO\@. LASCO has three CCD cameras whose operation is identical to that of EIT
except for slight difference in the parallel transfer time required by the
backside illumination. Thus, EIT appears to the LASCO electronics box as a
fourth LASCO camera and receives commands, data processing and telemetry access
through that instrument and shares 25\%\ of these resources. A discription of the
cameras, control electronics, software and data processing is presented in the
LASCO paper by Brueckner et al., 1995, in this volume and will not be duplicated
here.


\section{Instrument Response}

\subsection{Multilayer Optics}

     The multilayers were deposited on the EIT mirrors at the Institut
d'Optique, Centre Universitaire d'Orsay, France. Some of this work is described
by Chauvineau et al., 1991. Three of the four quadrants on each of the primary
and secondary mirrors were masked to allow multilayer deposition on only the
selected quadrants. A witness mirror was placed in close proximity to a flight
telescope mirror during each deposition. Thus, the reflectivities of these
witness mirrors should closely match those of the telescope mirrors.
Reflectivities of the witness mirrors were measured at the BESSY storage ring
in Berlin. The product of the primary and secondary witness sample
reflectivities for each quadrant are shown by the data points in Figures 8-11.
The dashed curves in these figures are the response curves calculated from the
design parameters of the multilayers and the optical constants of Windt et al.,
1988a and 1988b. Except for the case of the 284 \AA\ quadrant, these calculated
curves do not fit the witness mirror data well at wavelengths away from the
bandpass peak. This is likely due to small departures of layer thicknesses
from the design thicknesses during the multilayer deposition. Also, the
electron beam deposited materials, in this case, may have slightly different
optical constants from those measured by Windt et al.\ on sputtered materials.
The solid curves are the dashed curves that have been forced to fit the witness
sample data. Measurements of the flight telescope mirror's reflectivities are
presently being analyzed and will be used to produce the multilayer response
curves for analysis of the EIT solar images. 

\subsection{Filter Transmissions}

The transmission of the filters listed in Table I have been calculated
by using EUV absorption coefficients calculated from optical constants
derived by Henke et al., 199x.  In these calculations a 40 \AA\ layer of
Al$_2$O$_3$ was assumed to have formed on the exposed surfaces of the
aluminum.  Since the entrance filter and the CCD stray light filter are
fixed in the optical path, only the product of their transmissions are
shown in Figure 12.  This curve is the appropriate filter transmission
for the filter wheel in the open position.  Also included in the figure
are the total optical path transmissions for the filter wheel in
positions 0 and 1, listed in Table I. 

\subsection{CCD Quantum Efficiency}

The quantum efficiency of the flight CCD has been measured at seven wavelengths
in the range from 171 \AA\ to 1216 \AA\ as indicated in Figure 13.

\subsection{EIT Effective Areas}

\begin{figure}[p]
\newcommand{\pp}[1]{\parbox[t]{2.5in}{\raggedright #1}}
\vfill
\begin{center}
                        {\bf Table II: EIT Instrument Control Options}

\medskip
\footnotesize\setlength{\baselineskip}{11pt}
\begin{tabular}{ll}
\hline  \noalign{\vskip 2pt}
Bandpass Selection          &    1 of 4 by open quadrant shutter       \\
                            &                                          \\
Exposure length             &                                          \\
\quad mechanical shutter    &    \pp{minimum 140 ms, arbitrary
                                  length in 31 ms increments
                                  typical lowest exposure is 1.5 sec
                                  (the shorter exposures requires a special 
                                   operational mode)}                  \\
                            &                                          \\
\quad CCD frame transfer    &    0.25 sec                              \\
                            &                                          \\
Filter selection            &    Filter wheel, filters (cf.\ Table I)  \\
                            &                                          \\
CCD readout                 &    Full disk full resolution             \\
\quad On-chip summing       &    Full disk half resolution             \\
                            &    \quad ($2\times2$ pixel summed)       \\
                            &    Full disk quarter resolution          \\
                            &    \quad ($4\times4$ pixel summed)       \\
\quad Partial frame images  &    \pp{sub-array size and location
                                 selectable in blocks of $32\times32$ pixels}\\
                            &                                          \\
\multicolumn{2}{l}{On-board processing:  Data compression}             \\
                            &                                          \\
 Geometric Techniques       &    \pp{{\tt BadColAvg}: Replace `hot' column containing 
                                 CCD defect with average of adjacent columns 
                                 to allow maximum compression by further 
                                 techniques.}                          \\
                            &                                          \\
                            &    \pp{{\tt InterMin:} remove the effect of cosmic ray 
                                 ionization paths in the CCD by basically the 
                                 same technique and for the same reasons as 
                                 {\tt BadColAvg}.}                     \\
                            &                                          \\
                            &    \pp{{\tt Mask:} arbitrary pattern  can be transmitted by
                                 specifying a mask table of image blocks not 
                                 to be transmitted.}                   \\
                            &                                          \\
                            &    \pp{{\tt Subregion:} read out only a specified 
                                 rectangular region of the CCD. The subregions
                                 must be constructed of $32\times32$ pixel image 
                                 blocks (which also requires that the beginning
                                 pixel location is an integral multiple of 32).} \\
                            &                                          \\
                            &    \pp{{\tt PixSum:} sum pixels on readout of CCD, 
                                 typically no more than $4\times4$ pixel sums.}\\
                            &                                          \\
Coding Compression Techniques &                                        \\
			    &    Rice algorithm (lossless)             \\
                            &    ADCT: Adaptive Discrete Cosine Transform (lossy) \\
\hline
\end{tabular}
\end{center}
\end{figure}


\section{Instrument Control Options}

     The EIT has a number of instrument control options that may be selected by
commands uplinked from the ground via SoHO telemetry. These include bandpass
selection, exposure length, filter selection, CCD readout control and on-board
data processing options. Table II gives a summary of these options.  

Sub-arrays of pixels, each $32\times32$ ($83\times83$ arcsec) in size, may be read out while
the rest of the CCD field is discarded. This allows the limited EIT telemetry
to be used for detailed study of small areas of the sun with higher time
resolution. This option is implemented by clocking the parallel transfer gates
without driving the serial gates until the first row of the region of interest
is ready to enter the serial registers. Charge clocked in the serial registers
during this period is dissipated. After the first line of the selected
sub-array enters the serial registers the readout proceeds normally until the
last line is read. The rest of the image is then discarded as before. Data from
pixels in the same lines as the sub-array but lying outside the columns of
interest are discarded in the on-board processor. The time required to advance
charge in the parallel registers by one line is 480 $\mu$sec. The time
required to read out a line of pixels is 0.8 msec. Thus, the time
required to read a sub-array contained in $n$ lines of the CCD is $0.0208n + 0.492$
sec, where 0.492 sec is the time required to clock the parallel registers for
reading out the entire array. The minimum time between measurements of the
sub-array in this mode is then about 0.5 sec. 


\section{Predicted Response to Solar Phenomena}

                 (Ken Dere) (after Catura gets instrument response done)


\section{EIT Observational Programs and Operations}

\subsection{Observational Programs}
     
\subsubsection{Full Disk Observations}

EIT will produce a record of the corona over a multi-year period to permit
studies of its evolution with the solar cycle and the relationships of its
structure and physical properties to the initiation of the solar wind and to
events such as coronal mass ejections that produce disturbances in the
heliosphere. To obtain this synoptic archive, EIT will observe its full 
field of 42x42 arcmin in each of its four wavelength bands at least once per
calender day, and possibly more frequently, depending on the data compression
method that is selected. One image per day at each wavelength will be supplied 
to the SoHO Summary Data File, so that scientists not directly associated
with the SoHO mission will have access to overall views of the corona as 
quickly as is feasible. It is unlikely that the images in the Summary Data 
File will have the quality of definition and calibration that the fully 
processed data will have, but they will be adequate to provide an overview 
of the EUV corona to many non-specialists and the interested public.

The full-disk cadence will be programmed to operate when there is no contact
with the SoHO spacecraft. However, full-disk images may also be acquired
at the beginning of each long SoHO contact period when EIT is allotted an
enhanced telemetry rate to support CDS and SUMER science planning activities.

\subsubsection{Selected Areas Mode}

The SoHO telemetry assigned to EIT restricts its solar coverage to at most
a few full images per day. In order to achieve temporal resolution adequate to 
record the evolution of specific features such as the emergence and evolution
of coronal loops and processes of energy transport and deposition, the 
evolution of coronal holes, and the signatures of instabilities leading
to coronal mass ejections, EIT plans to execute observations on selected
solar areas with a temporal resolution appropriate to the phenomena being
investigated. Generally, EIT will observe sequences with a temporal cadence
of several minutes between observations, although shorter cadence intervals 
may at times be possible. The LASCO on-board computer enables the EIT CCD to
be read out in blocks of $32\times32$ pixels (nominally $80\times80$ arcsec). The locations
of such blocks are fixed on the CCD format (there are $32\times32$ blocks in the full 
$1024\times1024$ CCD pixel format), But single or multiple blocks may be read out to
define a field of view appropriate for the phenomenon being observed.

\subsection{Coordinated Observing Programs}

EIT will play an important role in supplementing the detailed spectroscopic
measurements obtained by CDS and SUMER with images of the coronal features 
being studied. Coordinated observations will be executed principally during
the eight hour contact period, as selection of appropriate coronal features 
(and near real-time adjustments of the fields of view of the CDS and SUMER
instruments) is essential for the success of these studies.

\subsection{EIT Operations}

\subsubsection{General}

EIT will be operated from the Experiment Operations Facility located at the
Goddard Space Flight Center, Greenbelt, MD. Operations will consist of the
preparation, verification and transmittal of commands designed to carry out
the desired observational sequences with the instrument. EIT's operational 
sequences are interleaved with LASCO commands, and are therefore an integral
part of the operational command sequences provided by LASCO to the EOF. As a
consequence, timing of all EIT operations, such as operations of motors,
interrogation of the CCD, on-board data compression and formatting of the 
data stream are integral with LASCO operations and cannot be altered on 
short notice. An exception is the specification of solar coordinates of
subsets of each image recorded on the EIT CCD\@. Such sub-images can be 
selected by uplink commands to the LASCO command memory during real-time 
observing programs coordinated with other SoHO instruments such as CDS and 
SUMER. 

\subsubsection{Routine Operations}

Routine operations are those that are executed on a regular basis, usually
on a daily basis with a minimum of alterations in the command sequences from
day-to-day. For EIT, the minimum set of routine or baseline observations are
full-sun images at the four EUV wavelengths, taken at least once per calender
day. Such operations will be executed via command routines that are stored in 
the LASCO command memory. No specific mission planning is required for these
synoptic observations except for coordination with LASCO observations, as
discussed above.

EIT observations taken with a higher telemetry rate allocation during a 
thirty minute interval at the beginning off the 8-hour contact period, for
the purpose of providing current solar EUV images to CDS and SUMER, will
also be regularly scheduled. If only solar sub-images are to be selected and
transmitted during this interval, it may be necessary to uplink commands 
specifying sub-frame size and location on the sun prior to data acquisition.

\subsubsection{Other Pre-planned Operations}

EIT will also execute observations of sub-areas of the sun designed to explore 
the evolution of coronal features over a wide range of temporal scales.
Such operations will be preplanned and executed in conjunction with LASCO
operations. Image cadence (temporal resolution) is limited by restrictions
on computer resources. (EIT is allocated about 20\%\ of LASCO's on-board
resources) and limitations on the total number of operations of EIT 
mechanical components (shutter, filter wheel, aperture control) over the
anticipated lifetime of the mission.

\subsubsection{Real-time of Near Real-time Operations}

Because of the interleaving of EIT and LASCO operations, a full real-time
flexibility in operating EIT is not possible. Operational sequences
(wavelength selection, image cadence, etc.) will again be pre-programmed,
but the selection of targets (which for EIT means the designation of which 
sub-areas of the CCD will be transmitted) will be decided in collaboration
with other SoHO experimenters. It is expected that sub-area selection may
be altered relatively quickly in rapid response to transient activity or 
other unexpected solar phenomenon. Such operations will take palace during 
the extended (8 hour) contact period.

\subsection{Operational Constraints on EIT}

Operational constraints are imposed by the fact that EIT command and data 
streams are integral with those of LASCO and by the limited telemetry
allocated to the EIT experiment. In general, the guidelines imposed by
these constraints are:

\begin{itemize}
\item Only one motor (in either LASCO or EIT) may be operated at any one time.

\item Only one camera (in either LASCO or EIT) may be read out at any one time.

\item EIT will use, on average, about 20\%\ of the total telemetry capability  
      and computer resources available to the EIT/LASCO experiments.

\item One full high resolution EIT image (or equivalant) may be stored in the
      on-board memory without data compression. Data compression routines
      that are available in the EIT/LASCO on-board computer allow the storage/
      transmission requirements for an image to be reduced by a factor of 2--4
      using a loss-less compression such as a square root or a ``Rice" algorithm.
      A compression factor of up to 10 may be obtained by the use of the Adaptive
      Discrete Cosine Transform algorithm is used, if some loss of information
      is acceptable.
\end{itemize}

\begin{center}
\large\bf                         Acknowledgements
\end{center}

Who will define this list?  Probably ought to get a list of names from J.-P. and Dan.

\begin{center}
\large\bf                         References
\end{center}

Brueckner, G.E., Howard, R.A., Kooman, M.J., Korendyke, C.M., Michels, D.J.,
Socker, D.G., Dere, K.P., Lamy, P.L., Liebaria, A., Bout, M.V., Schwenn, R.,
Simnet, G.M., Bedford, D.K. and Eyles, C.J., 1995, this volume.

Chauvineau, J.P., Clotaire, J.Y., Colas, G., Lam, O., Manneville, J.C., 
Marioge, J.P., Mullot, M., Raynal, A., Tissot, G., Valiergue, L.,
Delaboudiniere, J.P., 1991, Proc. SPIE, Multilayer and Grazing Incidence
X-ray/EUV Optics 1546, 576.

Delaboudiniere, J.P., Gabriel, G.H., Artzner, G.E., Michels, D., Dere, K.,
Howard, R., Catura, R., Stern, R., Lemen, J., Neupert, W., Cugnon, P.,
Koeckelenbergh, A., Van Dessel, E.L., Jamar, C., Maucherat, A., Chauvineau, J.
P., Marioge, J.P., 1989, ESA SP-1104, 43.

Henke et al..............

Tsuneta, S., Acton, L., Bruner, M., Lemen, J., Brown, W., Caravahlo, R.,
Catura, R., Freeland, S., Jurcevich, B., Morrison, M., Ogawara, Y., Hirayama,
T. and Owens, J., 1991, Solar Phys. 136, 37. 

Windt, D.L., Cash, W.C.Jr., Scott, M., Arendt, P., Newnam, B., Fisher, R.F.,
Swartzlander, A.B., 1988a, Appl. Opt. 27, 246.

Windt, D.L., Cash, W.C.Jr., Scott, M., Arendt, P., Newnam, B., Fisher, R.F.,
Swartzlander, A.B., 1988b, Appl. Opt. 27, 279.

Special Issue on Initial Results from Yohkoh, 1992, Publ. Astron. Soc. Japan, 
Vol. 44 No. 5.
                             Figure Captions

       Fig. 1 Sketch of EIT illustrating its operating principals
       Fig. 2a Photograph of the EIT flight instrument
       Fig. 2b Schematic of the EIT indicating its major telescope subsystems

\end{document}

