# 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. Sort 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