I guess so, you can say that some faster films have more silver than slower ones, but that isn't what makes them faster.
He said he phoned his friend in the laboratory and he said that: "Well, it is thicker, so it has more crystals"
I think all I have to say probably is: "Ok, but is that what makes it faster? Can I manufacture a fast film that has less crystals than a slow film?"
I believe that the question is more theoretical than practical, even though kodak might make 400 ISO films with more silver than 100 ISO, it doesn't mean that faster films will always have more silver than slower ones, since it is not one of the factors that determines the speed.
Yes. It must have bigger crystals (therefore fewer per unit mass) and higher iodide.
Originally Posted by had3l
The truth is that books written for teaching photography usually state that higher speed films contain more silver. They also state that high speed films are thicker.
That may well have been the case pre WWII, Ron knows how film emulsions have changed & evolved at EK since then.
A simple example to the question is given in my post #13. I would also say that the gelatin would go down in the faster film to pack the grains a bit more tightly, and that is my design consideration. A way to increase speed without increasing silver.
But that assumes that gelatin was thick enough to accomodate the larger grain in the first place. If the grains make the gelatin layer appear like sandpaper under a microscope, then the gelatin is too low and thickness must increase. Lowering gelatin if it is already too low can cause fog via contact sensitization.
All in all, this isn't simple and has to be tested. Ian is right, espicially from the historical aspect, due to the fact that early emulsions became less efficient as grain size increased. These were usually single run emulsions in which the iodide became increasingly buried (encapsulated and less efficient) as grain size went up. Ammonia digest only does so much before it causes fog.
Iodide on the surface can only go so high before it too causes fog via renucleation.
Therefore, modern double run emulsions have enabled the engineer to change the coating formula more freely as an additional option. This is evolution for you.
If you take a given emulsion, say 0.2 microns (pure bromide cubes with no finish of sulfur) and coate 50, 100, 200, 300 and etc. mg/ft square, threshold speed (inflection speed in the toe) will increase monotonically up to a given point and level off. Contrast will increase monotonically as well.
If you coat emulsions of 0.2, 0.4, 0.8, 1.0 and etc at the same level with all else being equal, again speed will go up but not level off. Usually, contrast will go down as developability of the emulsion and covering power of silver will decrease. Threshold speed will become more difficult to measure as contrast goes down. Silver will be adjusted to increase contrast, not speed!
Blending of 3 emulsions will place you in a mid point of coating parameters (silver and gelatin) for all speeds as far as is possible.
I have done all of these experiments BTW.
In any event, one learns from this how to turn knobs in design of a film to get the optimum position for a given emulsion.
Now, throw in grain type, sulfur and gold sensitization and all of the other factors such as development accelerators, hardness, antifoggants and you have the world of photo system engineering at its deadly finest.
I appreciate your comments Ian.
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Filmotec released these and other comprehensive data for two of their films. May be they are not actual...
Originally Posted by Photo Engineer
This thread has been most informative for me.
A couple of questions I have are that are monochrome emulsions multi layered? like say shingle on a beach? or is the emulsion very thin 1 or 2 layers deep?
I have read people on certain forums say that each film frame has 12 million or so 'grains' and that those grains when developed are black.
Their argument being that a 12mp digi-cam has the same resolution as film (doubtful) and that each photo site has 256 values when film can only be black or white.
Also I'd like to know if there is more than one sensitivity speck per grain, my understanding is that AgX has several silver molecules, that are bonded to other elements like Bromide ions, when a photo of light hits that element the silver is free to roam and seeks the sensitivity speck (silver and sulphur)?, I have also heard they use gold to make that process more reliable.
I hope there aren't too many questions, its just there is scant information on how film actually works.
Film emulsions are generally Ag/Br/I atoms combined into crystals from about 1 - 10 microns in size. They contain millions of atoms and many sensitivity specks which consist of sulfur and gold sites placed there along with dye.
When film develops, it can form anywhere from 3 silver metal atoms minimum up to the entire grain, and grains can be stacked, and therefore the dynamic range of density is analog in nature and virtually infinite. For practical purposes, it ranges from 0.1 - 3.0 density units in a normal negative B&W film.
Normal negative B&W films are single layers of light sensitive material sandwiched between an undercoate to help it stick to the film and prevent backscatter, and an overcoat to prevent scuff marks.
The emulsion itself can be a single emulsion or sometimes up to 3 emulsions mixed together in a single light sensitive layer.
For color film, this is far more complex. I have posted a diagram of the structure elsewhere.
There is, as I said elsewhere, a good article on this by Chuck Woodworth on the "how things work" site on the internet.
Do you have a URL?
Originally Posted by AgX
Ron, you could try FilmoTec GmbH the site is in English & German.
Originally Posted by Photo Engineer