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on the whole does everyone rate b/w film under or over? say for 100 asa film 80 or 125?

-- rodney carver (, November 18, 2000


Every time I've done my development calibrations the effective speed that I determine is lower than the film's rated speed. This has been true for three different developers although the change in speed was not the same for all three developing agents.

ISO speeds (ASA is gone now) are determined by a very specific set of exposure and development steps using a developer that is not commercially available. The whole system is there simply to provide a common ruler to allow different films to be compared. You will have to determine your effective speed by your own measurements.

But, not to dodge the question: I use PMK developer and rate HP5+ (ISO 400) at 250 and Delta 100 (ISO 100) at 64. These speeds produce a Zone I density of around 0.10.

-- Don Karon (, November 19, 2000.

After various field tests I've always had to downrate the ISO rate. However this varies with film type and developer combination. I've found the T-grain films to be fairly close to their published ratings. I now only use Delta 100 (both 4x5 and 120) which I rate at 80 (T-Max 100 was the same) and dev. in either Pyro or DiXactol (single bath).

-- Trevor Crone (, November 19, 2000.

One interesting exception to this is TMax 100 in Rodinol 1+50, which should be UPrated to ISO 125 (according to AGFA and my own tests). At this rating it gives better accutance than TechPan(!) and grain like Agfapan 25. It's a great combination. Most films developed in DIAFINE are faster than their advertised ratings.

-- Bill Mitchell (, November 19, 2000.

Most of the time when I do a film I get 1/3 stop higher speed, i.e., 160 for ISO 120.

Perhaps my shutters are slow, perhaps my Zone VI meter is calibrated to give more exposure that off the shelf meters--who knows. I only know it is repeatable.

-- Charlie Strack (, November 19, 2000.

Bill, what method (inversion scheme, Jobo rotary, etc.) and temperature do you use to get those results with T-Max 100 in Rodinal 1+50?

-- Sal Santamaura (, November 20, 2000.

Sal, single roll in old Nikor SS tank. I don't use a pre soak. Tap it on sucessive bottom corners to release bubbles. One minute of continuous agitation initially (the first 15 seconds the tank is inverted GENTLY), then 5 seconds every 30 seconds. The tank is picked up and gently rotated 30-45 degrees 5 times in 5 seconds using gentle wrist action. I put it down gently, and turn it 90 degrees so it's rotated on a different axis on every agitation. The agitation is GENTLE don't stop or start abruptly.

-- Bill Mitchell (, November 20, 2000.

You set the ASA, now called the ISO, at what the manufacturer puts on the box. Then you test a bit to see if your results are good at that stated speed. If not, you change it to what works for you and then call it your Exposure Index, YOUR tested speed for best results. It is just like getting a new car and finding out where the gas tank really goes dry. Before the mark, at the mark or well after the mark when you get past Empty to 'I'm not fooling' and the car stops.

-- Dan Smith (, November 23, 2000.

HI everyone This really confuses me, In this Black and White world of soooo many variables like the chemicals the temperatures and the water PH content and on the top of all, the subjects and perception of the image by a photographer, How can there be a generic way of doing things ?

Yet I accept this forum has improved my own chemistry to a great extent. Thanks Middle

-- middle (, November 24, 2000.

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