thawkins
Well-known
What is the practical difference (if any) between TRI X and Ilford's HP5 film? HP5 is more easily available locally than TRI X. And what about Delta 400? How does it differ from the other two films?
Ignore anyone who tells you that one is contrastier than the other: contrast is a function of development. Also ignore anyone who tells you they're not "really" ISO400: ISO film speed testing is quite firmly controlled.
Yes, they do look very slightly different. As mfogiel hints, this is mostly a consequence of the shape of the characteristic curve, especially on the toe. I prefer HP5 and my wife prefers Tri-X (but then, she and it were both born in Rochester NY). Neither of us hesitates for a moment to use the other's film if we run out of our own.
If you actually want to understand ISO speeds, take a look at http://www.rogerandfrances.com/subscription/ps iso speeds.html
Cheers,
R.
Also ignore anyone who tells you they're not "really" ISO400: ISO film speed testing is quite firmly controlled.
R.
Dear Chris,Roger,
A film's speed is dependent on the developer used. For the ISO measurements, there is a standardized developer used for that. In the real world, people often use developers that cause a drop in speed, and a few that increase it.
Example: Ilford HP5 gives me a speed of 400 in Tmax Developer, 320 in D-76 1+1, 320 in Rodinal 1+50, and 250 in PMK. Despite the speed loss, PMK is my favorite developer for it.
Dear Michael,it doesn't seem to be true for the 3200 ISO films, so why should it be true for 400 ISO?