Interesting post. Thank you. For the last 35 years I've nearly always referred to film Gamma Curves as H&D Cures.
Thanks Rafal!
Must have been an interesting time. Wet Collodion was better than any dry plates, but inconvenient. Amateurs demanded the more convenient dry plates even if it meant they were slower than what the pros used. And there were general quality and consistency issues that had to be resolved too...
(Your post led me to a preview online of .. Encyclopedia of 19th Century Photography By John Hannavy pg. 438 which briefly mentions H&D emulsion speed in a chapter on dry plate gelatin negatives)
That's where the trouble started, according to the correspondence unearthed by the article's author. Many dry plate manufacturers dreaded the idea of having a speed of their products measured by an independent, scientific method.
Sheppard and Mees note that "there has been considerable doubt thrown on the fundamental experiments upon which it has been founded" and that they intend to largely repeat those experiments, with better accuracy.In 1890 there was published by Messrs. Ferdinand Hurter and Vero C. Driffield, in the Journal of the Society of Chemical Industry, a paper entitled "Photo-chemical Investigations," in the course of which they gave for the first time a method of determining the sensitiveness of plates which depends on the measurement of a series of densities instead of a single reading.
Curiously, the modern speed systems have settled back on a single fixed density point being used, albeit with a specified (sort of) development contrast. If you've read Steven Benskins posts, he seems to be a fan of the "fractional-gradient speed method," which is more complicated. Stephen doesn't get much support for his viewpoint either. Just an interesting parallel.
Thanks Rafal!
Must have been an interesting time. Wet Collodion was better than any dry plates, but inconvenient. Amateurs demanded the more convenient dry plates even if it meant they were slower than what the pros used. And there were general quality and consistency issues that had to be resolved too...
(Your post led me to a preview online of .. Encyclopedia of 19th Century Photography By John Hannavy pg. 438 which briefly mentions H&D emulsion speed in a chapter on dry plate gelatin negatives)
Not quite right. Even the first dry plates were faster than wet plates and it didn't take long for them to become much faster. The reason dry plate manufacturers resisted accurate testing was because it might interfere with the outlandish speed claims each was making to best the others. Which is faster: Extra High Speed or Ultra High Speed?"
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