I have seen the use of the term "acutance" to describe modern B&W films?
What are the characteristics of a modern B&W film as opposed to a traditional one? Is it merely a question of single versus multple emulsion layers, or are there other more important considerations. And which films are modern? I assume that the T-grain emulsion films such as TMAX-100 and TMAX-400 would be considred modern. But what about a film like FP4+ that has been around a long time more or less in its present incarnation? Would it be considered a traditional or modern film?
Among onther things:
An acutance film is one with reduced internal reflections. This is accomplished by adding an acutance dye to the film. This dye decreases speed though, so you need a fast emulsion with fine enough grain to allow the use of added dyes to improve sharpness without a severe penalty in grain.
It has lower turbidity by means of having more transparent grains, thereby reducing scatter. This is often achieved with very thin t-grains, thinner gelatin layers, or lower levels of coated silver with beter developability (a greater % of active grains vs 'dead' grains).
It has higher edge effects by using higher iodide levels or having more iodide on the surface of the grain. It can also achieve this by having inhibitors in the film that are released by the emulsion during development. An example of this is a chromogenic B&W film or any color negative film.
Hope this helps.
Originally Posted by Photo Engineer
Thanks for the useful information.
What you say about the use of thin t-grains and thinner gelatin layers to decrease turbidity makes sense. But what is the mechanism that results in less internal reflections with the use of a dye?
Imagine the light being reflected an infinite distance within the coating by bouncing off old style K (klunker) grains. They can then travel quite a distance (in microns) from the 1 micron grain in a high speed K-grain film. This could cause exposure where you don't want it to take place. The absorbing (acutance) dye attenuates this reflection but at the same time reduces speed.
Originally Posted by sanking
The dye also trims speed so that ISO can be more constant from batch to batch.
These dyes are the colored dyes that wash out of films when you dump the first solution out of your developing tank.
They are also used in color paper to trim the speeds of the various layers and improve sharpness in the multilayer structure.
A common dye, used in Matrix Film and also used in old blue sensitive films was Tartrazine. However, since the eye is not sensitve to yellow image sharpness (we see the sharpness of mainly cyan and magenta dyes), it is not really necessary except in Matrix Film or B&W films only sensitive to blue. If you have an ortho or pan film, then you need to use mixtures of dyes. That is why the 'runoff' from the first processing solution is brown or green. Those are the dyes chosen to optimize that particular film for sharpness plus trim speeds.
One would think that thinner layers also helps just due to the fact that the layers are thinner. The layers are still 3D, and there are active grains distributed stochastically in X, Y, and Z. The Z dimension is interesting because grains are not in line as light penetrates the depth of the coating, allowing exposure of overlapping grain structures. The effect on the image would be of larger grain, and lower accutance. That is, less of an ability to image a thin straight line due to the overlapping grain structure; the line would be bumpy and would "blur" if you will.
Originally Posted by Photo Engineer
Then again, I could be completely wrong. Wouldn't be the first time. Won't be the last either. What say you, Photo Engineer?
Sponsored Ad. (Subscribers to APUG have the option to remove this ad.)
If there is no turbidity, and the light strikes at a 90 deg angle, then the T-grains may be considered to be acting as half silvered mirrors with the light passing through or exposing, and as the light penetrates deeper and deeper into the film, it is attenuated. This takes place due to the fact that grains are stacked.
Originally Posted by Bruce Watson
Of course, with turbidity and reflection (scatter) what you say is true also. as some grains are not stacked, or light hits an edge and etc.
In any case, the edge effects produced during development assist to 'trim' up the edges.
The simple test of the ratio of the effect between all of these is to make white light knife edge exposures and soft x-ray exposures (these latter will not be affected by any scatter or reflection). The ratio of the measured line spread in the two sets of exposure vs desired line width as actually found on the chart used will give you a measure of the ratio of chemical to physical effects, and the size at which the effects are maximized for sharpness will show what format (35/MF/LF) the film will be most effective at. Usually, a design goal is to have these adjusted so all 3 formats will be optimum.
Of course, this is not always possible, but a happy medium can be obtained, which is what we always are faced with - a series of compromises for the best of all of these.
Film/developer combinations that show the adjacency effect are said to have high acutance (strictly acutance is the edge density slope).It's possible to estimate the adjacency effect by photographing a light grey card on a black card,stand developing in rodinal 1:200 for 90min and making a 10x enlargement of the grey/black interface.Adjacency effect shows as a light line at the interface.
Some films that show the effect:Adox CHS 100, Plus-X, HP5, Tri-X.
Some films with little or no effect (hard to tell):T-max 100, Delta 100, Delta 400, Pan F, FP4, Lucky SHD 100 New, Acros.
In my test the word acutance separates the films quite well, the word modern not very well.
"I have seen the use of the term "acutance"
to describe modern B&W films?"
Acutance, hardly a "modern" term. Going so far
back as 70 years ago Willi Beutler was formulating
high acutance developers for the slow thin emulsion
films of the day. Adox KB14 or a film of it's type may
have been one Tech. Pan was perhaps 30 years
latter; 40 years ago?
"What are the characteristics of a modern B&W film
as opposed to a traditional one?"
Incorporated hardeners. Automated machine processing
spurred their incorporation. T films are noted for their
high temperature endurance. When were they
introduced, 15 - 20 years ago?
"And which films are modern?"
Modern, in my mind, equates with incorporated hardeners.
As I've mentioned the spur was high speed high temperature
machine processing. In that respect, and from what I've
read, T films are more recent modern films.
"But what about a film like FP4+ that has been around ..."
FP4+, is a modern film but not one which would generally
be considered a purely acutance film.
In the beginning their were soft emulsions, acid stops,
and hardener incorporated fixers. Traditional films should
receive in-the-beginning processing. Dan
I think that the point here is that there are HA films and NA (normal acutance?) films and HA developers and NA developers. Along with this are all of the degrees and combinations of all of these.
The use of these combinations is what leadz to the infinite variety of results we get with analog film, and also leads to the reason we disagree sometimes as to result. In any event, this almost infinite variation is what enchants me about film vs digital which is like driving a nail into the creativity processes and fixing them to someone elses desired result.
The near infinite variations that can be obtained were known for years at EK and that is why there were so many films and so many film developers. This was not unique to EK, as other companies did much the same.
I was not surprised by the use of the term "acutance" to describe developers, which as you observe has been used for decades, but as an adjective to describe film. The term has not been widely used, at least from my readings, to describe films. Even though it is clear that modern T-grain films such as TMAX-100 and TMAX-400 have much better native resolution than traditonal films of same ASA such as Plus-X, FP4+, TRI-X, HP5+, etc.
Originally Posted by dancqu