John Pazmino
 NYSkies Astronomy Inc
 1992 February 1
[This was a two-part article published in 1992 January and February. 
Here they are assembled into on piece under the later date.]
    One highlight of the [fall 1991] AAVSO Cambridge meeting was the 
CCD workshop convened on Friday afternoon 25 October [1991]. AAVSO 
from time to time stages workshops on new technologies or major 
situations in observational astronomy. This workshop was the first on 
CCDs and a second one is planned for the spring 1992 convention in 
Columbus OH. 
    The workshop was a survey of CCD apparatus for the home astronomer 
with the potential for use in photometry. The discussions were carried 
in several short papers and demos and by a panel fielding questions 
from the floor. The lecture room, at AAVSO's HQ, was filled to its 60-
seat capacity. 
    A CCD, standing for 'charged couple device', is a computer chip 
that converts light impinging on it into a computer digital signal. 
The chip has a grid of cells, or pixels, that cover the focal plane 
area of a telescope. A typical CCDchip for home use has 192 X 256 
pixels on a patch about 5mm square. Each pixel receives light (and 
other EMR) from a tiny but specific place in the focal plane and the 
whole image is then assembled by computer from the signals from all 
the pixels. The brightness of a pixel in the reconstituted image on 
the screen is consonant with the signal strength from the 
corresponding pixel on the chip. 
    Because the image is a stream of computer signals, it can, besides 
be displayed evanescently on the screen, be captured into a discfile. 
In this form the image can be sent by mail to other astronomers, sent 
by telcomms to other computers, saved for later review, and even 
combined into other images. Also because the image is in a computer 
form it can be massaged in astounding ways: remove flaws, correct 
distortion, add color, sharpen detail, to cite only a few. 
    While the CCD technique has been employed at observatories for 
about 15 years, it was barred from home use by the necessity for heavy 
computing power and the overall expense of the apparatus. The 
breakthru for home enjoyment of CCDs came in about 1985. By then the 
personal computer became cheap, powerful, and standardized enough to 
be regarded as a home appliance. Today CCD equipment is sold without 
the attendent computer, for anyone entering the field reasonably has 
    Home astronomers during the 1980s tried to acquire CCD experience 
by tinkering with camcorders and security/surveillance cameras. Results 
were encouraging yet half-baked and, in general, work was abandoned 
after even valiant and heroic efforts. 
    Now there are two main suppliers of home CCD equipment: Santa 
Barbara Instrument Group and SpectraSource Instruments. The former, 
from Santa Barbara CA, beefed up a satellite star tracker into a 
workable CCD outfit. The latter, from Westlake Village CA, developed 
an allnew CCD apparatus under the brandname Lynxx. Both equipages come 
with the CCDchip encased in a protective head, computer software, 
power supply, and assorted cables and fittings. 
    In its simplest elements the CCD captures a 'television' picture 
of the focal plane and the computer displays this 'television' image. 
It is on the whole easy to capture good and pretty pictures of the 
celestial objects. It is far simpler than regular astrophotography 
    CCDs are to regular cameras as camcorders are to movie cameras. 
One telling feature of this workshop -- and of AAVSO meetings in 
general for the last 8 or 10 years -- is the routine tapings by 
camcorder. In all the prior history of AAVSO, back to its inception in 
1911, tho cinecameras were readily available, there are pitifully few 
films of AAVSO procedings! One surely will eat guano before going back 
to cinefilm again, right? 
    In the early days of CCDs there were many computer systems, each
out of touch with the other. Many astronomers were stymied when they 
tried to use images or accessories from a one system with an other. By 
now everything is based on the IBM system. The few remaining off-IBM 
systems accommodated to IBM with emulator boards or software. There 
are few genuine complaints of system incompatibility anymore. 
    AAVSO is into CCDgraphy, as it may be termed, for its potential in 
photometry, the assessment of the illumination received from the 
stars. AAVSO has a long-running program of electrophotometry employing 
analog photomultiplier heads and circuit electronics. In fact, 
electrophotometry in the United States was largely promoted and 
developed thru AAVSO. 
    But this photometry never matured and remains today a wildly 
capricious endeavor. AAVSO accumulated an alltime total of barely 
5,000 electrophotometric observations, versus over six millions from 
eyeball inspection of the stars. 
    Despite the boon and bonanza of going on the road of CCD, many and 
major issues were uncovered in the workshop. Right off the bat, the 
astronomer must be well grounded in computer operations. It can be 
argued that this is a skill not ordinarily found among the public. 
Yet, given the brief history of home computers, there are orders more 
people litterate in computers than in electronics. Or, for that 
matter, ordinary photography. Computers are taught (however ineptly) 
in the primary schools; electronics and photography are not. 
    A truly solidly mounted and stable telescope is required, just as 
for photography and electrophotometry. One can not make do with a rig 
assembled for each session on a rooftop. Some believe that with the 
very short exposure (integration) time a less-than-substantial mount 
is adequate. Not so; the image is blurred exactly as for photography. 
    The CCDchip has a tiny area, around 5mm square. This is an awfully 
tiny part of the focal plane! The scope must have means to aim and set 
and track on that small area. Even with an offaxis or a flip-mirror 
guider the task of getting the target onto the CCDchip can be 
positively maddening 
    An other consequence of the tiny receptor in the CCDchip is the 
allegedly lousy images displayed on the computer screen. Everything is 
fuzzy and the stars are gross blobs. What's going on here?! The piece 
of the focal plane captured by the chip is enlarged and zoomed to fit 
on the screen. 
    So the Ring Nebula, to pick one example, may stand perhaps 20 
degrees across. To achieve this same angular extent for the Ring 
Nebula in an eyeball view thru the telescope requires a optical 
magnification of about TWELVE HUNDRED! (The Ring is about an arcminute 
in true diameter.) Go pump up a homesize scope to 1200 power and how 
does the Ring Nebula look? Lousy. 
    The computer is an integral part of the CCD circuit and ideally it 
should stand at the telescope. The astronomer must work the computer 
during the CCDgraphy session and the CCDhead must be cabled to it. 
This is often not practical or possible if the machine is a regular 
desktop. A new other computer may be required, a laptop, small and 
compact and lightweight. 
    The images are stored on magnetic media, which are vulnerable to 
damage, both physical and digital. The usual media available to home 
astronomers are not viable for true archiving of data. Also, there is 
the fear, not unrealistic given the recent experiences of NASA and 
USGS, that in future years the media will be undecipherable. For the 
machines that write and read them will be irretrievably abandoned. 
    There are many and incompatible file formats for the digital 
images. The Santa Barbara files, for instance, are useless for the 
SpecraSource software. There are emerging some utilities to convert 
among formats, but in any conversion some information is lost. 
    So far the operator is at the mercy of the equipment company to 
furnish the software. There is not yet an independent software 
industry for CCDs. Never the less, there is a fount of general purpose 
image processing applications that can handle selected file formats. 
Already astronomers are pressing into service applications developed 
for the various space missions. 
    CCDgrams are black-&-white images. Each pixel holds one of the, 
normally, 256 grayscale values. In computer terms, each pixel occupies 
one byte of memory. All those gorgeous colors in textbook and magazine 
repros of CCDgrams are artificially inserted by the CCD astronomer. 
    They are arbitrarily assigned to the grayscale values according as 
the intent and purpose at hand. Hence, it is ridiculous to interpret 
these colors with no initimacy with the original experiment by with 
the CCDgrams were captured. They are, for the disinterested audience, 
really just false, but often fabulous, colorations. 
    There are only few and poor catalogs, charts, atlases of the sky 
at the deep faint limits of the home CCD. A CCDgram from a 200mm scope 
can record 15th magnitude stars. There just are no complete surveys or 
census of the heavens at 15th magnitude. One can litterally be lost 
among the stars. 
    There was hope that the Guide Star Catalog would be the roadmap 
into CCDgraphy. Alas, as the travails of Hubble brought out, the GSC 
is too full of knots for reliable astronomy. 
    Paralleling this is the lack of AAVSO standard stars and magnitude 
sequences. Without these it's tough to assess the magnitude of a 
variable star with any competence. True, one could cite the boxing in 
by brightness of the target star between other stars. But the 
comparison stars taken by opportunity may be unstable in light or have 
spectral complications. 
    As yet there are no commercial applications for photometry with 
CCDs. There is some bundled with particular CCD outfits. This is not 
transferible to other CCD rigs. Everything on the market is for 
collecting fullfield pictures, wonderful and beautiful, yes, but in 
themselves hardly valid for photometry. 
    In the workshop the slides were of hit-or-miss quality. The 
speakers took pictures, via regular camera, of the computer screen. 
Sometimes the edge of the display unit showed around the edge of the 
picture! That's because there is still no cheap, quick, and satisfying 
way to get a hardcopy replica -- not a crummy printer output -- of the 
displayed image. (The presented results also do highlight the lack of 
camera litteracy in the populance!) 
    It is realisticly infeasible to build a CCD rig from scratch. The 
cost and trouble will so far excede that of getting a commercial unit. 
And there is little more instruction or knowledge gained this way over 
studying the storebought unit. 
    This is quite different from telescope building. Altho hardy a 
means of saving costs, building a telescope yields understanding and 
insight to optics and mechanics not easily obtained from merely 
working a storebought instrument. 
    Finally, from this workshop, there is the glatt immaturity in the 
instructions and documentations accompanying the CCD outfits. Altho 
the apparatus may be well designed, built, and crafted, the paperwork 
is useless. It really takes a well-read and wisely astronomer to dope 
out what is going on. Many noted round after round of calls to the 
company for resolving questions. Others recounted the obligation to 
seek for themselves other people expert in CCDgraphy to help them.
    The AAVSO workshop was a signal step toward appreciating this new 
animal, the CCD system, and everyone is eagerly looking toward the 
next workshop at the Columbus meeting.