Plate Classes
Every plate is assign a class designation to indicate the type of exposure that was taken. The following table comes primarily from the Harvard Annals, Vol 26, page 9.
The list from the above references is incomplete and does not account for all of the classes that appear in the database. These additional classes are marked with the derived note and given a description that follows the examples given in the above reference. Nevertheless, there are still several classes that must be marked unknown class until additional information is available.
Note: a chart plate is an ordinary plate that documents the sky, like a patrol plate.
There are currently 72 plate classes in the database.
Class | Class Description | Notes |
A | trails on North and South Poles | B plates only |
B | trails of stars between +65 and +85 | B plates only |
C | multiple exposure calibration plate, 2 or more fields, blue (class C plates calibrate with Pole or Harvard Standard Regions) | Nov 1933 Cambridge, Jan 1934 Bloemfontein |
C | trails of stars between +55 and +65 at upper and lower culmination, to determine atmospheric absorption | B plates only |
C1 | calibration plate, yellow plate with filter | Nov 1933 Cambridge, Jan 1934 Bloemfontein |
C2 | calibration plate, red plate with filter | Nov 1933 Cambridge, Jan 1934 Bloemfontein |
CS | multiple exposure calibration out of focus (soft focus) blue plate | derived |
D | trails of stars between -30 and +55 | B plates only |
D | spectrum plate, high dispersion prism, blue plate | Nov 1933 Cambridge, Jan 1934 Bloemfontein |
D1 | high dispersion spectrum widened, blue plate | Combo example |
D1 | spectrum plate, high dispersion prism, yellow plate w/filter | Nov 1933 Cambridge, Jan 1934 Bloemfontein |
D2 | spectrum plate, high dispersion prism, red plate w/filter | Nov 1933 Cambridge, Jan 1934 Bloemfontein |
E | spectra of stars near the poles | B plates only |
Ec | unknown class | derived |
Er | unknown class | derived |
F | focus plate, blue | Nov 1933 Cambridge, Jan 1934 Bloemfontein |
F | spectra of stars near the zenith | B plates only |
F1 | focus plate, yellow with filter | Nov 1933 Cambridge, Jan 1934 Bloemfontein |
F2 | focus plate, red with filter | Nov 1933 Cambridge, Jan 1934 Bloemfontein |
FD1 | focus plate with prism, yellow filter | Combo example |
G | grating used on chart plate | Nov 1933 Cambridge, Jan 1934 Bloemfontein |
G | spectra of stars near the equator | B plates only |
H | chart plate long exposure (previous designation was L) | Nov 1933 Cambridge, Jan 1934 Bloemfontein |
H | charts of stars, generally with exposures of 1 hour | B plates only |
I | spectrum plate, long dispersion | Combo example |
I | spectra of stars with exposures of about 1 hour | B plates only |
J | trails of stars near the equator | B plates only |
K | test plates on the poles, trails of 10 min., first with, and then without, prism. | B plates only |
L | chart, single exposure, in focus blue-sensitive plate (MAJORITY) | Nov 1933 Cambridge, Jan 1934 Bloemfontein |
L | charts of stars between +47 and +57, - 5 and -7, and -17 with exposures of about 15 minutes | B plates only |
L1 | chart, single exposure, in focus yellow-sensitive with filter | Nov 1933 Cambridge, Jan 1934 Bloemfontein |
L2 | chart, single exposure, in focus red-sensitive with filter | Nov 1933 Cambridge, Jan 1934 Bloemfontein |
L2S | chart, single exposure, in focus red-sensitive with filter out of focus (soft focus) | derived |
L3 | chart, single exp. with other than the 3 standard colors | Nov 1933 Cambridge, Jan 1934 Bloemfontein |
L4 | chart, single exp. but UV or any special filter | Nov 1933 Cambridge, Jan 1934 Bloemfontein |
LS | chart, single exposure, in focus blue-sensitive out of focus (soft focus) plate | derived |
Lgi | guided single exposure on blue plate, moving object | Combo example |
Li | chart, single exposure, in focus blue-sensitive trailed plate | derived |
M | miscellaneous photographs not included in the above classes | B plates only |
M | multiple exposure on one field, blue | Nov 1933 Cambridge, Jan 1934 Bloemfontein |
M1 | multiple exposure on one field, yellow with filter | Nov 1933 Cambridge, Jan 1934 Bloemfontein |
M2 | multiple exposure on one field, red with filter | Nov 1933 Cambridge, Jan 1934 Bloemfontein |
M2S | multiple image with red screen, red plate with filter, out of focus (!!) | Combo example |
MG | multiple exposure on one field, blue, grating used on chart plate | derived |
MS | multiple exposure on one field, out of focus (soft focus) blue plate | derived |
MS2 | multiple image with red screen, red plate with filter, out of focus | derived |
Ms | unknown class | derived |
N | unknown class | derived |
O | spectrum plate, short dispersion | Nov 1933 Cambridge, Jan 1934 Bloemfontein |
OS | spectrum plate, soft dispersion out of focus (soft focus) | derived |
P | polar adjustment (chart) C, D trails, 2 exposures | Nov 1933 Cambridge, Jan 1934 Bloemfontein |
PG | polar adjustment (chart) C, D trails, 2 exposures grating used on chart plate | derived |
Pan | Pannekoek: blue plates, multiple exposure taken on AC patrol camera ca. 1924-25 | Combo example |
Pole | unknown class | derived |
R | unknown class | derived |
S | out of focus (soft focus) blue plate | Nov 1933 Cambridge, Jan 1934 Bloemfontein |
S1 | out of focus (soft focus) yellow plate with filter | Nov 1933 Cambridge, Jan 1934 Bloemfontein |
S2 | out of focus (soft focus) red plate with filter | Nov 1933 Cambridge, Jan 1934 Bloemfontein |
SM | multiple exposure on one field, out of focus (soft focus) blue plate | derived |
T | out of focus plate | Nov 1933 Cambridge, Jan 1934 Bloemfontein |
T1 | two exposures, different fields | Nov 1933 Cambridge, Jan 1934 Bloemfontein |
TM | multiple exposure on one field, blue, out of focus | derived |
U | large prisms | Nov 1933 Cambridge, Jan 1934 Bloemfontein |
VR | unknown class | derived |
W | Milky Way | Combo example |
X | unknown class | derived |
d | spectrum plate, low dispersion prism, blue | Nov 1933 Cambridge, Jan 1934 Bloemfontein |
d1 | spectrum plate, low dispersion prism, yellow | Nov 1933 Cambridge, Jan 1934 Bloemfontein |
d2 | spectrum plate, low dispersion prism, red | Nov 1933 Cambridge, Jan 1934 Bloemfontein |
g | guided plate | Nov 1933 Cambridge, Jan 1934 Bloemfontein |
i | trailed plate | Nov 1933 Cambridge, Jan 1934 Bloemfontein |
l | unknown class | derived |