. The microscope; an introduction to microscopic methods and to histology. Microscopes; 1899. CH. VIII. PHO TO-MICROGRA PH Y. 197 than for ordinary photography. The ordinary negative is liable to have too much contrast, but this is rarely the case with photo-micro- graphs. Any good developer may be used. One can as a rule do no better than to follow the directions accompanying the plates used. The writer's experience has been so satisfactory with Mr. Walmsley's developers that he desires to call attention to them. The developers are easily made, will develop anything that can be developed and
. The microscope; an introduction to microscopic methods and to histology. Microscopes; 1899. CH. VIII. PHO TO-MICROGRA PH Y. 197 than for ordinary photography. The ordinary negative is liable to have too much contrast, but this is rarely the case with photo-micro- graphs. Any good developer may be used. One can as a rule do no better than to follow the directions accompanying the plates used. The writer's experience has been so satisfactory with Mr. Walmsley's developers that he desires to call attention to them. The developers are easily made, will develop anything that can be developed and one can feel confident that if the negative is not good the fault does not lie with the developer. The best photo-micrographic negatives made by the writer were made with Cramer's instantaneous isochromatic plates, and the image com- menced to appear with Walmsley's developer in 21; to 3 minutes and the development was completed in 12 to 15 minutes. Excellent nega- tives have been developed in less time and also when it required half an hour to develop them. The temperature has much to do with the development of correct!}' exposed negatives, so that no rule can be given. Metol and rodinal developers have also given excellent results and in a shorter time. If one desires the best possible results it is necessary to avoid the light in developing. Even the ruby light of the dark room should be avoided as much as possible, for the plates used are made purposely sensitive to the longer rays of the spectrum (§ 193). After the nega- tive is developed and washed it should not be taken to the light till it is fixed. Too much light after development and before fixing, injures the clearness of the negative. Fig. 153. Focusing Glass. " It is achromatic, con- sisting of a double convex crown lens and a negative meniscus flint lens cemented ; It screws into the brass tube and is thus adjustable, enabling one to focus the pencil mark in the clear area of the focusing scree
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