A panchromatic plate or film is one 
which is sensitive to all the colors of 
the spectrum, thus differing from the 
ordinary plate which is insensitive to 
red and orange, and but slightly sensi¬ 
tive to yellow. An orthochromatic or 
isochromatic plate is one which is sensi¬ 
tive to yellow, and to a slight degree 
to orange, but not to red. Both pan¬ 
chromatic and orthochromatic plates 
and films must be used with a yellow 
filter to reduce the influence of the 
highly actinic blue and violet rays, and 
give the colors of the subject the true 
tone-value as seen by the eye. The 
amount of this “correction,” as it is 
called, will vary with the depth of the 
filter employed. The light yellow K 
filter gives some correction, the deeper 
K, gives more, the still deeper K gives 
full correction, and on some subjects 
the very deep G filter gives better re¬ 
sults by over-emphasizing the yellow- 
red end of the spectrum. Naturally 
the deeper the filter the longer the 
exposure required. Orthochromatic 
plates, especially those of the “non¬ 
filter” or “self-screen” type (in which 
a dye acting as a filter is incorporated 
-in the emulsion) may be used for sub¬ 
jects which contain no red, and such 
plates as the Imperial Non-filter, Ilford 
Screened Chromatic, and Wellington 
Anti-screen, especially if used with a 
K, filter, give very good results with a 
great many subjects. The superiority 
of colour rendering given by pan¬ 
chromatic plates and films, and the fact 
that much shorter exposures with any 
given filter are required than with 
orthochromatic material, offsets the 
disadvantage that these plates must be 
handled in complete darkness. Several 
brands of panchromatic plates are now 
on the market, such as the Ilford 
Special Rapid Panchromatic, the Wrat- 
ten and Wainwright Panchromatic, and 
the Imperial Panchromatic, while a 
color-sensitive cut film is provided in 
the Eastman Commercial Panchromatic 
Film. 
GENERAL NOTES ON THE USE OF EQUIP¬ 
MENT IN THE FIELD 
Test all equipment, especially new 
apparatus, thoroughly before taking it 
into the field. 
Take all the plates or films you think 
you are likely to require—and three 
dozen more. 
Carry an extra focussing screen. 
The one in use may not break for 
years, or it may break to-morrow. 
Learn to tell the sensitive side of a 
plate by feeling the extreme corner 
with a perfectly dry finger. If in doubt 
the following test may be used on un¬ 
backed plates (not on backed plates or 
films). Bite the corner with the well- 
bared teeth, then open the mouth 
slowly. The side which sticks to the 
teeth is the coated side. Cut films 
Page 333 
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slnd Health on Both!' 
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Don’t forget to include a can 
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outfit. 
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In writing to Advertisers mention Forest and Stream. It will identify you. 
