what is t-grain?

Hello,

Sorry for my ignorance, but i would like to know what is t-grain film

and what are its pros and MOST OF ALL its cons. The difference

between regular film? One wrote that they are either loved or hated,

and id like to know why. Thanks to all,

James

Here's my understanding, I'm sure somebody will correct me if I oversimplify to

the point of error:

Silver halide is a cubic crystal. It's suspended in a layer of gelatin.

Kodak figured out how to dope silver halide so that forms "tabular" crystals.

As the name implies, they are 'flatter ' than conventional silver halide, and

thus somewhat more efficient at capturing light: it presents more surface area

to the light for a given amount of silver, which allows a thinner emulsion.

Effectively, t-grain gives a faster film for a given grain size - or, looked at the

other way, finer grain at the same film speed.

The 'love or hate' business is mostly an aesthetic response: the new 't-grain'

films have a distinctly different look, and a somewhat different response curve

when compared to the 'old fashioned' films.

T-grain films typically take a bit longer to fix, and are a bit harder to wash,

which can be annoying if you have to adjust your porcessing.

Dear James,

Traditional silver halide grains vary widely in size and are more or less cubical in their crystal structure. A fast film has a lot of small crystals in among the big ones. The big ones are easier for a photon to hit and therefore make for a faster film. Slower films are made up of smaller crystals.

Monosize crystals (as the word 'monosize' suggests) are much more uniform and can therefore provide a more controllable film speed -- which happily translates into smaller grain for a given speed.

Not all monosize crystals are tabular: Kodak's 'tabular' or T-grains are monosize, and so are Ilford's epitaxial-growth Delta grains, but the latter are NOT tabular. Nor is Foma's T200 tabular, despite its name (in fact, it's a good cubic-emulsion film of ISO 125-160 in most developers).

Most monosize crystals are more sensitive to over- or underexposure and over- or underdevelopment than traditional cubic, and have a smaller 'developer repertoire' (i.e. behave well in fewer developers). Delta is a good deal more tolerant than T-Grain, and delivers higher sharpness, but the grain is coarser speed-for-speed. Poor exposure and/or development imply greater loss of shadow detail (under) or coarser grain (over) with monosize dispersions.

T-grain also has a high orange sensitivity, for reasons that would fill another post.

The net result is that the tonality of 'traditional' and 'monosize' tend to differ, and the further out-of-spec the monosize exposure and development are, the less attractive most people find the results.

Get your exposure spot-on, and use the right developer for the right time, and you MAY prefer monosize. But there are plenty who are fully in control and still prefer cubic.

Finally, the differences between monosize and cubic can be exaggerated. All manufacturers try to blend the technologies to some extent, so a modern cubic-crystal film (such as Ilford HP5 Plus) and a modern monosize film (such as the current Ilford Delta 400, a vastly better and rather faster film than the original Delta 400) tend to be a good deal more similar than the original versions of either.

Hope this helps. You may also want to look at some of the free modules in The Photo School at www.rogerandfrances.com, especially those dealing with ISO speeds and 'Welcome to Film'.

Cheers,

Roger (every week in AP)

Thanks everyone. From what i understood (sintheticaly) t-grain is "suppost" to be better quality for a given speed but is more complex to deal with, both for latitude and develpoment. Ill stick to tri-x. Thanks again.

James