9.6.
PHOTOGRAPHIC PLATES
311
unfortunate name that had been applied to this emulsion, years before
it became useful to scientists for more than lantern slides. It is, in fact,
a slow orthochromatic fine-grained emulsion with good, but not excessive, contrast characteristics. It is now spread on plates as a particularly
thin layer so that there is a minimum of gelatin to be de-gassed before
a good vacuum can be obtained. This is still the plate of choice, recommended by the the manufacturer for most electron microscopy. It is a
rare occasion indeed, when an electron microscopist can legitimately
blame this plate for inferior quality in his work.
The Kodak Spectrographic Plate, Type V-O has a substantially finergrained emulsion than the Lantern Slide Plate as a comparison of Figs.
37(a) and (b) will show. However, this is apparent only when the images
are excessively enlarged photographically. The microscope and the nature
of the specimen is more apt to limit resolution than the grain of the
plate. The two plates have nearly the same contrast values, but the
Spectrographic V-O Plate has only about one quarter the speed to electrons of the Lantern Slide Plate. This slow speed is a serious disadvantage.
The Ilford N.40 Process Plate and the Gevaert Diapositive Contrast
Plate seem to have approximately the same emulsion as the Kodak
Lantern Slide Plate, although this writer cannot speak from personal
experience. For microscopes which use film, Kodak recommends their
Fine Grain Positive Film, and the other companies have the equivalent.
Emulsions which are designed primarily for photoengraving can be
used when extreme contrast is needed. Their use is to be discouraged for
most histological work for most gray tones would be lost and the micrographs be too harsh. They have their use in high magnification work
where the contrast scale is narrow and the principal interest is in line.
Therefore they are particularly useful for some types of macromolecular
studies. In this category, the Kodak Company recommends Kodalith
Ortho Plates, used with a special Kodalith, D-85 developer. The Ilford
Company recommends their N.60 Photomechanical Plate, used with a
special ID-13 developer. The Gevaert Company has similar emulsions on
plates.
On the whole it is advisable for the individual investigator to settle
down with one plate that he can obtain easily, and then learn to exploit
its desirable properties to the fullest. His troubles will be compounded
in a variety of ways if he chooses an excessively contrasty plate when his
problems do not require it.
It is a necessary precaution, at least with the products of some man-
PHOTOGRAPHIC PLATES
311
unfortunate name that had been applied to this emulsion, years before
it became useful to scientists for more than lantern slides. It is, in fact,
a slow orthochromatic fine-grained emulsion with good, but not excessive, contrast characteristics. It is now spread on plates as a particularly
thin layer so that there is a minimum of gelatin to be de-gassed before
a good vacuum can be obtained. This is still the plate of choice, recommended by the the manufacturer for most electron microscopy. It is a
rare occasion indeed, when an electron microscopist can legitimately
blame this plate for inferior quality in his work.
The Kodak Spectrographic Plate, Type V-O has a substantially finergrained emulsion than the Lantern Slide Plate as a comparison of Figs.
37(a) and (b) will show. However, this is apparent only when the images
are excessively enlarged photographically. The microscope and the nature
of the specimen is more apt to limit resolution than the grain of the
plate. The two plates have nearly the same contrast values, but the
Spectrographic V-O Plate has only about one quarter the speed to electrons of the Lantern Slide Plate. This slow speed is a serious disadvantage.
The Ilford N.40 Process Plate and the Gevaert Diapositive Contrast
Plate seem to have approximately the same emulsion as the Kodak
Lantern Slide Plate, although this writer cannot speak from personal
experience. For microscopes which use film, Kodak recommends their
Fine Grain Positive Film, and the other companies have the equivalent.
Emulsions which are designed primarily for photoengraving can be
used when extreme contrast is needed. Their use is to be discouraged for
most histological work for most gray tones would be lost and the micrographs be too harsh. They have their use in high magnification work
where the contrast scale is narrow and the principal interest is in line.
Therefore they are particularly useful for some types of macromolecular
studies. In this category, the Kodak Company recommends Kodalith
Ortho Plates, used with a special Kodalith, D-85 developer. The Ilford
Company recommends their N.60 Photomechanical Plate, used with a
special ID-13 developer. The Gevaert Company has similar emulsions on
plates.
On the whole it is advisable for the individual investigator to settle
down with one plate that he can obtain easily, and then learn to exploit
its desirable properties to the fullest. His troubles will be compounded
in a variety of ways if he chooses an excessively contrasty plate when his
problems do not require it.
It is a necessary precaution, at least with the products of some man-